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Updated: July 2017
 
 

parallel (1)

Name

parallel - build and execute shell command lines from standard input in parallel

Synopsis

parallel [options] [command [arguments]] < list_of_arguments

parallel [options] [command [arguments]] ( ::: arguments | ::::
argfile(s) ) ...

parallel --semaphore [options] command

#!/usr/bin/parallel --shebang [options] [command [arguments]]

Description

PARALLEL(1)                        parallel                        PARALLEL(1)



NAME
       parallel - build and execute shell command lines from standard input in
       parallel

SYNOPSIS
       parallel [options] [command [arguments]] < list_of_arguments

       parallel [options] [command [arguments]] ( ::: arguments | ::::
       argfile(s) ) ...

       parallel --semaphore [options] command

       #!/usr/bin/parallel --shebang [options] [command [arguments]]

DESCRIPTION
       GNU parallel is a shell tool for executing jobs in parallel using one
       or more computers. A job can be a single command or a small script that
       has to be run for each of the lines in the input. The typical input is
       a list of files, a list of hosts, a list of users, a list of URLs, or a
       list of tables. A job can also be a command that reads from a pipe. GNU
       parallel can then split the input into blocks and pipe a block into
       each command in parallel.

       If you use xargs and tee today you will find GNU parallel very easy to
       use as GNU parallel is written to have the same options as xargs. If
       you write loops in shell, you will find GNU parallel may be able to
       replace most of the loops and make them run faster by running several
       jobs in parallel.

       GNU parallel makes sure output from the commands is the same output as
       you would get had you run the commands sequentially. This makes it
       possible to use output from GNU parallel as input for other programs.

       For each line of input GNU parallel will execute command with the line
       as arguments. If no command is given, the line of input is executed.
       Several lines will be run in parallel. GNU parallel can often be used
       as a substitute for xargs or cat | bash.

   Reader's guide
       Before looking at the options you may want to check out the EXAMPLEs
       after the list of options. That will give you an idea of what GNU
       parallel is capable of.

       You can also watch the intro video for a quick introduction:
       http://tinyogg.com/watch/TORaR/ http://tinyogg.com/watch/hfxKj/ and
       http://tinyogg.com/watch/YQuXd/ or
       http://www.youtube.com/playlist?list=PL284C9FF2488BC6D1

OPTIONS
       command  Command to execute.  If command or the following arguments
                contain replacement strings (such as {}) every instance will
                be substituted with the input.

                If command is given, GNU parallel solve the same tasks as
                xargs. If command is not given GNU parallel will behave
                similar to cat | sh.

                The command must be an executable, a script, a composed
                command, or a function. If it is a function you need to export
                -f the function first. An alias will, however, not work (see
                why http://www.perlmonks.org/index.pl?node_id=484296).

       {}       Input line. This replacement string will be replaced by a full
                line read from the input source. The input source is normally
                stdin (standard input), but can also be given with -a, :::, or
                ::::.

                The replacement string {} can be changed with -I.

                If the command line contains no replacement strings then {}
                will be appended to the command line.

       {.}      Input line without extension. This replacement string will be
                replaced by the input with the extension removed. If the input
                line contains . after the last / the last . till the end of
                the string will be removed and {.} will be replaced with the
                remaining. E.g. foo.jpg becomes foo, subdir/foo.jpg becomes
                subdir/foo, sub.dir/foo.jpg becomes sub.dir/foo, sub.dir/bar
                remains sub.dir/bar. If the input line does not contain . it
                will remain unchanged.

                The replacement string {.} can be changed with --er.

                To understand replacement strings see {}.

       {/}      Basename of input line. This replacement string will be
                replaced by the input with the directory part removed.

                The replacement string {/} can be changed with
                --basenamereplace.

                To understand replacement strings see {}.

       {//}     Dirname of input line. This replacement string will be
                replaced by the dir of the input line. See dirname(1).

                The replacement string {//} can be changed with
                --dirnamereplace.

                To understand replacement strings see {}.

       {/.}     Basename of input line without extension. This replacement
                string will be replaced by the input with the directory and
                extension part removed. It is a combination of {/} and {.}.

                The replacement string {/.} can be changed with
                --basenameextensionreplace.

                To understand replacement strings see {}.

       {#}      Sequence number of the job to run. This replacement string
                will be replaced by the sequence number of the job being run.
                It contains the same number as $PARALLEL_SEQ.

                The replacement string {#} can be changed with --seqreplace.

                To understand replacement strings see {}.

       {n}      Argument from input source n or the n'th argument. This
                positional replacement string will be replaced by the input
                from input source n (when used with -a or ::::) or with the
                n'th argument (when used with -N).

                To understand replacement strings see {}.

       {n.}     Argument from input source n or the n'th argument without
                extension. It is a combination of {n} and {.}.

                This positional replacement string will be replaced by the
                input from input source n (when used with -a or ::::) or with
                the n'th argument (when used with -N). The input will have the
                extension removed.

                To understand positional replacement strings see {n}.

       {n/}     Basename of argument from input source n or the n'th argument.
                It is a combination of {n} and {/}.

                This positional replacement string will be replaced by the
                input from input source n (when used with -a or ::::) or with
                the n'th argument (when used with -N). The input will have the
                directory (if any) removed.

                To understand positional replacement strings see {n}.

       {n//}    Dirname of argument from input source n or the n'th argument.
                It is a combination of {n} and {//}.

                This positional replacement string will be replaced by the dir
                of the input from input source n (when used with -a or ::::)
                or with the n'th argument (when used with -N). See dirname(1).

                To understand positional replacement strings see {n}.

       {n/.}    Basename of argument from input source n or the n'th argument
                without extension.  It is a combination of {n}, {/}, and {.}.

                This positional replacement string will be replaced by the
                input from input source n (when used with -a or ::::) or with
                the n'th argument (when used with -N). The input will have the
                directory (if any) and extension removed.

                To understand positional replacement strings see {n}.

       ::: arguments
                Use arguments from the command line as input source instead of
                stdin (standard input). Unlike other options for GNU parallel
                ::: is placed after the command and before the arguments.

                The following are equivalent:

                  (echo file1; echo file2) | parallel gzip
                  parallel gzip ::: file1 file2
                  parallel gzip {} ::: file1 file2
                  parallel --arg-sep ,, gzip {} ,, file1 file2
                  parallel --arg-sep ,, gzip ,, file1 file2
                  parallel ::: "gzip file1" "gzip file2"

                To avoid treating ::: as special use --arg-sep to set the
                argument separator to something else. See also --arg-sep.

                stdin (standard input) will be passed to the first process
                run.

                If multiple ::: are given, each group will be treated as an
                input source, and all combinations of input sources will be
                generated. E.g. ::: 1 2 ::: a b c will result in the
                combinations (1,a) (1,b) (1,c) (2,a) (2,b) (2,c). This is
                useful for replacing nested for-loops.

                ::: and :::: can be mixed. So these are equivalent:

                  parallel echo {1} {2} {3} ::: 6 7 ::: 4 5 ::: 1 2 3
                  parallel echo {1} {2} {3} :::: <(seq 6 7) <(seq 4 5) :::: <(seq 1 3)
                  parallel -a <(seq 6 7) echo {1} {2} {3} :::: <(seq 4 5) :::: <(seq 1 3)
                  parallel -a <(seq 6 7) -a <(seq 4 5) echo {1} {2} {3} ::: 1 2 3
                  seq 6 7 | parallel -a - -a <(seq 4 5) echo {1} {2} {3} ::: 1 2 3
                  seq 4 5 | parallel echo {1} {2} {3} :::: <(seq 6 7) - ::: 1 2 3

       :::: argfiles
                Another way to write -a argfile1 -a argfile2 ...

                ::: and :::: can be mixed.

                See -a, ::: and --xapply.

       --null
       -0       Use NUL as delimiter.  Normally input lines will end in \n
                (newline). If they end in \0 (NUL), then use this option. It
                is useful for processing arguments that may contain \n
                (newline).

       --arg-file input-file
       -a input-file
                Use input-file as input source. If you use this option, stdin
                (standard input) is given to the first process run.
                Otherwise, stdin (standard input) is redirected from
                /dev/null.

                If multiple -a are given, each input-file will be treated as
                an input source, and all combinations of input sources will be
                generated. E.g. The file foo contains 1 2, the file bar
                contains a b c.  -a foo -a bar will result in the combinations
                (1,a) (1,b) (1,c) (2,a) (2,b) (2,c). This is useful for
                replacing nested for-loops.

                See also --xapply and {n}.

       --arg-file-sep sep-str
                Use sep-str instead of :::: as separator string between
                command and argument files. Useful if :::: is used for
                something else by the command.

                See also: ::::.

       --arg-sep sep-str
                Use sep-str instead of ::: as separator string. Useful if :::
                is used for something else by the command.

                Also useful if you command uses ::: but you still want to read
                arguments from stdin (standard input): Simply change --arg-sep
                to a string that is not in the command line.

                See also: :::.

       --basefile file
       --bf file
                file will be transferred to each sshlogin before a jobs is
                started. It will be removed if --cleanup is active. The file
                may be a script to run or some common base data needed for the
                jobs.  Multiple --bf can be specified to transfer more
                basefiles. The file will be transferred the same way as
                --transfer.

       --basenamereplace replace-str
       --bnr replace-str
                Use the replacement string replace-str instead of {/} for
                basename of input line.

       --basenameextensionreplace replace-str
       --bner replace-str
                Use the replacement string replace-str instead of {/.} for
                basename of input line without extension.

       --bg     Run command in background thus GNU parallel will not wait for
                completion of the command before exiting. This is the default
                if --semaphore is set.

                See also: --fg, man sem

                Implies --semaphore.

       --bibtex Print the BibTeX entry for GNU parallel.

       --block size
       --block-size size
                Size of block in bytes. The size can be postfixed with K, M,
                G, T, P, k, m, g, t, or p which would multiply the size with
                1024, 1048576, 1073741824, 1099511627776, 1125899906842624,
                1000, 1000000, 1000000000, 1000000000000, or 1000000000000000
                respectively.

                GNU parallel tries to meet the block size but can be off by
                the length of one record. For performance reasons size should
                be bigger than a single record.

                size defaults to 1M.

                See --pipe for use of this.

       --cleanup
                Remove transferred files. --cleanup will remove the
                transferred files on the remote computer after processing is
                done.

                  find log -name '*gz' | parallel \
                    --sshlogin server.example.com --transfer --return {.}.bz2 \
                    --cleanup "zcat {} | bzip -9 >{.}.bz2"

                With --transfer the file transferred to the remote computer
                will be removed on the remote computer.  Directories created
                will not be removed - even if they are empty.

                With --return the file transferred from the remote computer
                will be removed on the remote computer.  Directories created
                will not be removed - even if they are empty.

                --cleanup is ignored when not used with --transfer or
                --return.

       --colsep regexp
       -C regexp
                Column separator. The input will be treated as a table with
                regexp separating the columns. The n'th column can be access
                using {n} or {n.}. E.g. {3} is the 3rd column.

                --colsep implies --trim rl.

                regexp is a Perl Regular Expression:
                http://perldoc.perl.org/perlre.html

       --delimiter delim
       -d delim Input items are terminated by the specified character.  Quotes
                and backslash are not special; every character in the input is
                taken literally.  Disables the end-of-file string, which is
                treated like any other argument.  This can be used when the
                input consists of simply newline-separated items, although it
                is almost always better to design your program to use --null
                where this is possible.  The specified delimiter may be a
                single character, a C-style character escape such as \n, or an
                octal or hexadecimal escape code.  Octal and hexadecimal
                escape codes are understood as for the printf command.
                Multibyte characters are not supported.

       --dirnamereplace replace-str
       --dnr replace-str
                Use the replacement string replace-str instead of {//} for
                dirname of input line.

       -E eof-str
                Set the end of file string to eof-str.  If the end of file
                string occurs as a line of input, the rest of the input is
                ignored.  If neither -E nor -e is used, no end of file string
                is used.

       --dry-run
                Print the job to run on stdout (standard output), but do not
                run the job. Use -v -v to include the ssh/rsync wrapping if
                the job would be run on a remote computer. Do not count on
                this literaly, though, as the job may be scheduled on another
                computer or the local computer if : is in the list.

       --eof[=eof-str]
       -e[eof-str]
                This option is a synonym for the -E option.  Use -E instead,
                because it is POSIX compliant for xargs while this option is
                not.  If eof-str is omitted, there is no end of file string.
                If neither -E nor -e is used, no end of file string is used.

       --env var (beta testing)
                Copy environment variable var. This will copy var to the
                environment that the command is run in. This is especially
                useful for remote environments.

                Caveat: If var contains newline ('\n') the value is messed up.

       --eta    Show the estimated number of seconds before finishing. This
                forces GNU parallel to read all jobs before starting to find
                the number of jobs. GNU parallel normally only reads the next
                job to run.  Implies --progress.

       --fg     Run command in foreground thus GNU parallel will wait for
                completion of the command before exiting.

                See also: --bg, man sem

                Implies --semaphore.

       --filter-hosts (alpha testing)
                Remove down hosts. For each remote host: check that login
                through ssh works. If not: do not use this host.

                Currently you can <i>not</i> put --filter-hosts in a profile,
                $PARALLEL, /etc/parallel/config or similar. This is because
                GNU parallel uses GNU parallel to compute this, so you will
                get an infinite loop. This will likely be fixed in a later
                release.

       --gnu    Behave like GNU parallel. If --tollef and --gnu are both set,
                --gnu takes precedence.

       --group  Group output. Output from each jobs is grouped together and is
                only printed when the command is finished. stderr (standard
                error) first followed by stdout (standard output). This takes
                some CPU time. In rare situations GNU parallel takes up lots
                of CPU time and if it is acceptable that the outputs from
                different commands are mixed together, then disabling grouping
                with -u can speedup GNU parallel by a factor of 10.

                --group is the default. Can be reversed with -u.

       --help
       -h       Print a summary of the options to GNU parallel and exit.

       --halt-on-error <0|1|2>
       --halt <0|1|2>
                0  Do not halt if a job fails. Exit status will be the number
                   of jobs failed. This is the default.

                1  Do not start new jobs if a job fails, but complete the
                   running jobs including cleanup. The exit status will be the
                   exit status from the last failing job.

                2  Kill off all jobs immediately and exit without cleanup. The
                   exit status will be the exit status from the failing job.

       --header regexp
                Use upto regexp as header. For normal usage the matched header
                (typically the first line: --header '\n') will be split using
                --colsep (which will default to '\t') and column names can be
                used as replacement variables: {column name}. For --pipe the
                matched header will be prepended to each output.

                --header : is an alias for --header '\n'.

       -I replace-str
                Use the replacement string replace-str instead of {}.

       --replace[=replace-str]
       -i[replace-str]
                This option is a synonym for -Ireplace-str if replace-str is
                specified, and for -I{} otherwise.  This option is deprecated;
                use -I instead.

       --joblog logfile
                Logfile for executed jobs. Save a list of the executed jobs to
                logfile in the following TAB separated format: sequence
                number, sshlogin, start time as seconds since epoch, run time
                in seconds, bytes in files transferred, bytes in files
                returned, exit status, and command run.

                To convert the times into ISO-8601 strict do:

                perl -a -F"\t" -ne 'chomp($F[2]=`date -d \@$F[2] +%FT%T`);
                print join("\t",@F)'

                See also --resume.

       --jobs N
       -j N
       --max-procs N
       -P N     Number of jobslots. Run up to N jobs in parallel.  0 means as
                many as possible. Default is 100% which will run one job per
                CPU core.

                If --semaphore is set default is 1 thus making a mutex.

       --jobs +N
       -j +N
       --max-procs +N
       -P +N    Add N to the number of CPU cores.  Run this many jobs in
                parallel.  See also --use-cpus-instead-of-cores.

       --jobs -N
       -j -N
       --max-procs -N
       -P -N    Subtract N from the number of CPU cores.  Run this many jobs
                in parallel.  If the evaluated number is less than 1 then 1
                will be used.  See also --use-cpus-instead-of-cores.

       --jobs N%
       -j N%
       --max-procs N%
       -P N%    Multiply N% with the number of CPU cores.  Run this many jobs
                in parallel.  If the evaluated number is less than 1 then 1
                will be used.  See also --use-cpus-instead-of-cores.

       --jobs procfile
       -j procfile
       --max-procs procfile
       -P procfile
                Read parameter from file. Use the content of procfile as
                parameter for -j. E.g. procfile could contain the string 100%
                or +2 or 10. If procfile is changed when a job completes,
                procfile is read again and the new number of jobs is computed.
                If the number is lower than before, running jobs will be
                allowed to finish but new jobs will not be started until the
                wanted number of jobs has been reached.  This makes it
                possible to change the number of simultaneous running jobs
                while GNU parallel is running.

       --keep-order
       -k       Keep sequence of output same as the order of input. Normally
                the output of a job will be printed as soon as the job
                completes. Try this to see the difference:

                  parallel -j4 sleep {}\; echo {} ::: 2 1 4 3
                  parallel -j4 -k sleep {}\; echo {} ::: 2 1 4 3

       -L max-lines
                When used with --pipe: Read records of max-lines (alpha
                testing).

                When used otherwise: Use at most max-lines nonblank input
                lines per command line.  Trailing blanks cause an input line
                to be logically continued on the next input line.

                -L 0 means read one line, but insert 0 arguments on the
                command line.

                Implies -X unless -m, --xargs, or --pipe is set.

       --max-lines[=max-lines]
       -l[max-lines]
                When used with --pipe: Read records of max-lines (alpha
                testing).

                When used otherwise: Synonym for the -L option.  Unlike -L,
                the max-lines argument is optional.  If max-lines is not
                specified, it defaults to one.  The -l option is deprecated
                since the POSIX standard specifies -L instead.

                -l 0 is an alias for -l 1.

                Implies -X unless -m, --xargs, or --pipe is set.

       --load max-load
                Do not start new jobs on a given computer unless the load is
                less than max-load. max-load uses the same syntax as --jobs,
                so 100% for one per CPU is a valid setting. Only difference is
                0 which is interpreted as 0.01.

                The load average is only sampled every 10 seconds using uptime
                to avoid stressing small computers. Only the first (1 minute)
                load is used.

       --controlmaster (experimental)
       -M (experimental)
                Use ssh's ControlMaster to make ssh connections faster. Useful
                if jobs run remote and are very fast to run. This is disabled
                for sshlogins that specify their own ssh command.

       --xargs  Multiple arguments. Insert as many arguments as the command
                line length permits.

                If {} is not used the arguments will be appended to the line.
                If {} is used multiple times each {} will be replaced with all
                the arguments.

                Support for --xargs with --sshlogin is limited and may fail.

                See also -X for context replace. If in doubt use -X as that
                will most likely do what is needed.

       -m       Multiple arguments. Insert as many arguments as the command
                line length permits. If multiple jobs are being run in
                parallel: distribute the arguments evenly among the jobs. Use
                -j1 to avoid this.

                If {} is not used the arguments will be appended to the line.
                If {} is used multiple times each {} will be replaced with all
                the arguments.

                Support for -m with --sshlogin is limited and may fail.

                See also -X for context replace. If in doubt use -X as that
                will most likely do what is needed.

       --minversion version
                Print the version GNU parallel and exit.  If the current
                version of GNU parallel is less than version the exit code is
                255. Otherwise it is 0.

                This is useful for scripts that depend on features only
                available from a certain version of GNU parallel.

       --nonall --onall with no arguments. Run the command on all computers
                given with --sshlogin but take no arguments. GNU parallel will
                log into --jobs number of computers in parallel and run the
                job on the computer. -j adjusts how many computers to log into
                in parallel.

                This is useful for running the same command (e.g. uptime) on a
                list of servers.

       --onall  Run all the jobs on all computers given with --sshlogin. GNU
                parallel will log into --jobs number of computers in parallel
                and run one job at a time on the computer. The order of the
                jobs will not be changed, but some computers may finish before
                others. -j adjusts how many computers to log into in parallel.

                When using --group the output will be grouped by each server,
                so all the output from one server will be grouped together.

       --output-as-files
       --outputasfiles
       --files  Instead of printing the output to stdout (standard output) the
                output of each job is saved in a file and the filename is then
                printed.

       --pipe
       --spreadstdin
                Spread input to jobs on stdin (standard input). Read a block
                of data from stdin (standard input) and give one block of data
                as input to one job.

                The block size is determined by --block. The strings
                --recstart and --recend tell GNU parallel how a record starts
                and/or ends. The block read will have the final partial record
                removed before the block is passed on to the job. The partial
                record will be prepended to next block.

                If --recstart is given this will be used to split at record
                start.

                If --recend is given this will be used to split at record end.

                If both --recstart and --recend are given both will have to
                match to find a split position.

                If neither --recstart nor --recend are given --recend defaults
                to '\n'. To have no record separator use --recend "".

                --files is often used with --pipe.

       --plain (beta testing)
                Ignore any --profile, $PARALLEL, ~/.parallel/config, and
                --tollef to get full control on the command line (used by GNU
                parallel internally when called with --sshlogin).

       --progress
                Show progress of computations. List the computers involved in
                the task with number of CPU cores detected and the max number
                of jobs to run. After that show progress for each computer:
                number of running jobs, number of completed jobs, and
                percentage of all jobs done by this computer. The percentage
                will only be available after all jobs have been scheduled as
                GNU parallel only read the next job when ready to schedule it
                - this is to avoid wasting time and memory by reading
                everything at startup.

                By sending GNU parallel SIGUSR2 you can toggle turning on/off
                --progress on a running GNU parallel process.

                See also: --eta

       --max-args=max-args
       -n max-args
                Use at most max-args arguments per command line.  Fewer than
                max-args arguments will be used if the size (see the -s
                option) is exceeded, unless the -x option is given, in which
                case GNU parallel will exit.

                -n 0 means read one argument, but insert 0 arguments on the
                command line.

                Implies -X unless -m is set.

       --max-replace-args=max-args
       -N max-args
                Use at most max-args arguments per command line. Like -n but
                also makes replacement strings {1} .. {max-args} that
                represents argument 1 .. max-args. If too few args the {n}
                will be empty.

                -N 0 means read one argument, but insert 0 arguments on the
                command line.

                This will set the owner of the homedir to the user:

                tr ':' '\n' < /etc/passwd | parallel -N7 chown {1} {6}

                Implies -X unless -m or --pipe is set.

                When used with --pipe -N is the number of records to read.
                This is much slower than --block so avoid it if performance is
                important.

       --max-line-length-allowed
                Print the maximal number of characters allowed on the command
                line and exit (used by GNU parallel itself to determine the
                line length on remote computers).

       --number-of-cpus
                Print the number of physical CPUs and exit (used by GNU
                parallel itself to determine the number of physical CPUs on
                remote computers).

       --number-of-cores
                Print the number of CPU cores and exit (used by GNU parallel
                itself to determine the number of CPU cores on remote
                computers).

       --nice niceness
                Run the command at this niceness. For simple commands you can
                just add nice in front of the command. But if the command
                consists of more sub commands (Like: ls|wc) then prepending
                nice will not always work. --nice will make sure all sub
                commands are niced.

       --interactive
       -p       Prompt the user about whether to run each command line and
                read a line from the terminal.  Only run the command line if
                the response starts with 'y' or 'Y'.  Implies -t.

       --profile profilename
       -J profilename
                Use profile profilename for options. This is useful if you
                want to have multiple profiles. You could have one profile for
                running jobs in parallel on the local computer and a different
                profile for running jobs on remote computers. See the section
                PROFILE FILES for examples.

                profilename corresponds to the file ~/.parallel/profilename.

                You can give multiple profiles by repeating --profile. If
                parts of the profiles conflict, the later ones will be used.

                Default: config

       --quote
       -q       Quote command.  This will quote the command line so special
                characters are not interpreted by the shell. See the section
                QUOTING. Most people will never need this.  Quoting is
                disabled by default.

       --no-run-if-empty
       -r       If the stdin (standard input) only contains whitespace, do not
                run the command.

                If used with --pipe this is slow.

       --recstart startstring
       --recend endstring
                If --recstart is given startstring will be used to split at
                record start.

                If --recend is given endstring will be used to split at record
                end.

                If both --recstart and --recend are given the combined string
                endstringstartstring will have to match to find a split
                position. This is useful if either startstring or endstring
                match in the middle of a record.

                If neither --recstart nor --recend are given then --recend
                defaults to '\n'. To have no record separator use --recend "".

                --recstart and --recend are used with --pipe.

                Use --regexp to interpret --recstart and --recend as regular
                expressions. This is slow, however.

       --regexp Use --regexp to interpret --recstart and --recend as regular
                expressions. This is slow, however.

       --remove-rec-sep
       --removerecsep
       --rrs    Remove the text matched by --recstart and --recend before
                piping it to the command.

                Only used with --pipe.

       --results prefix (beta testing)
       --res prefix (beta testing)
                Results in files named by tab separated arguments. Save the
                output into files. The file names will be prefixed with prefix
                which can contain a path with a prefix string. The file with
                output from stdout (standard output) will prefixed with
                'prefixstdout'.  The file with output from stderr (standard
                error) will prefixed with 'prefixstderr'.

                The postfix is the header of the input source (if using
                --header :) or the number of the input source followed by the
                value of the input source. This is repeated for every input
                source and is separated by TAB (\t).

                E.g:

                  parallel --header : --results foo/bar echo {a} {b} ::: a I II ::: b III IIII

                will generate the files:

                  foo/barstderr a       I       b       III
                  foo/barstderr a       I       b       IIII
                  foo/barstderr a       II      b       III
                  foo/barstderr a       II      b       IIII
                  foo/barstdout a       I       b       III
                  foo/barstdout a       I       b       IIII
                  foo/barstdout a       II      b       III
                  foo/barstdout a       II      b       IIII

                and

                  parallel --results foo/bar echo {1} {2} ::: 1 2 ::: 3 4

                will generate the files:

                  foo/barstderr 1       I       2       III
                  foo/barstderr 1       I       2       IIII
                  foo/barstderr 1       II      2       III
                  foo/barstderr 1       II      2       IIII
                  foo/barstdout 1       I       2       III
                  foo/barstdout 1       I       2       IIII
                  foo/barstdout 1       II      2       III
                  foo/barstdout 1       II      2       IIII

                where all spaces are TABs (\t);.

                See also --files, --header, --joblog.

       --resume Resumes from the last unfinished job. By reading --joblog GNU
                parallel will figure out the last unfinished job and continue
                from there. As GNU parallel only looks at the sequence numbers
                in --joblog then the input, the command, and --joblog all have
                to remain unchanged; otherwise GNU parallel may run wrong
                commands.

                See also: --joblog.

       --retries n
                If a job fails, retry it on another computer. Do this n times.
                If there are fewer than n computers in --sshlogin GNU parallel
                will re-use the computers. This is useful if some jobs fail
                for no apparent reason (such as network failure).

       --return filename
                Transfer files from remote computers. --return is used with
                --sshlogin when the arguments are files on the remote
                computers. When processing is done the file filename will be
                transferred from the remote computer using rsync and will be
                put relative to the default login dir. E.g.

                  echo foo/bar.txt | parallel \
                    --sshlogin server.example.com --return {.}.out touch {.}.out

                This will transfer the file $HOME/foo/bar.out from the
                computer server.example.com to the file foo/bar.out after
                running touch foo/bar.out on server.example.com.

                  echo /tmp/foo/bar.txt | parallel \
                    --sshlogin server.example.com --return {.}.out touch {.}.out

                This will transfer the file /tmp/foo/bar.out from the computer
                server.example.com to the file /tmp/foo/bar.out after running
                touch /tmp/foo/bar.out on server.example.com.

                Multiple files can be transferred by repeating the options
                multiple times:

                  echo /tmp/foo/bar.txt | \
                    parallel --sshlogin server.example.com \
                    --return {.}.out --return {.}.out2 touch {.}.out {.}.out2

                --return is often used with --transfer and --cleanup.

                --return is ignored when used with --sshlogin : or when not
                used with --sshlogin.

       --max-chars=max-chars
       -s max-chars
                Use at most max-chars characters per command line, including
                the command and initial-arguments and the terminating nulls at
                the ends of the argument strings.  The largest allowed value
                is system-dependent, and is calculated as the argument length
                limit for exec, less the size of your environment.  The
                default value is the maximum.

                Implies -X unless -m is set.

       --show-limits
                Display the limits on the command-line length which are
                imposed by the operating system and the -s option.  Pipe the
                input from /dev/null (and perhaps specify --no-run-if-empty)
                if you don't want GNU parallel to do anything.

       --semaphore
                Work as a counting semaphore. --semaphore will cause GNU
                parallel to start command in the background. When the number
                of simultaneous jobs is reached, GNU parallel will wait for
                one of these to complete before starting another command.

                --semaphore implies --bg unless --fg is specified.

                --semaphore implies --semaphorename `tty` unless
                --semaphorename is specified.

                Used with --fg, --wait, and --semaphorename.

                The command sem is an alias for parallel --semaphore.

                See also: man sem

       --semaphorename name
       --id name
                Use name as the name of the semaphore. Default is the name of
                the controlling tty (output from tty).

                The default normally works as expected when used
                interactively, but when used in a script name should be set.
                $$ or my_task_name are often a good value.

                The semaphore is stored in ~/.parallel/semaphores/

                Implies --semaphore.

                See also: man sem

       --semaphoretimeout secs (not implemented)
                If the semaphore is not released within secs seconds, take it
                anyway.

                Implies --semaphore.

                See also: man sem

       --seqreplace replace-str
                Use the replacement string replace-str instead of {#} for job
                sequence number.

       --shellquote
                Does not run the command but quotes it. Useful for making
                quoted composed commands for GNU parallel.

       --skip-first-line
                Do not use the first line of input (used by GNU parallel
                itself when called with --shebang).

       -S [ncpu/]sshlogin[,[ncpu/]sshlogin[,...]]
       --sshlogin [ncpu/]sshlogin[,[ncpu/]sshlogin[,...]]
                Distribute jobs to remote computers. The jobs will be run on a
                list of remote computers.  GNU parallel will determine the
                number of CPU cores on the remote computers and run the number
                of jobs as specified by -j.  If the number ncpu is given GNU
                parallel will use this number for number of CPU cores on the
                host. Normally ncpu will not be needed.

                An sshlogin is of the form:

                  [sshcommand [options]][username@]hostname

                The sshlogin must not require a password.

                The sshlogin ':' is special, it means 'no ssh' and will
                therefore run on the local computer.

                The sshlogin '..' is special, it read sshlogins from
                ~/.parallel/sshloginfile

                The sshlogin '-' is special, too, it read sshlogins from stdin
                (standard input).

                To specify more sshlogins separate the sshlogins by comma or
                repeat the options multiple times.

                For examples: see --sshloginfile.

                The remote host must have GNU parallel installed.

                --sshlogin is known to cause problems with -m and -X.

                --sshlogin is often used with --transfer, --return, --cleanup,
                and --trc.

       --sshloginfile filename
       --slf filename
                File with sshlogins. The file consists of sshlogins on
                separate lines. Empty lines and lines starting with '#' are
                ignored. Example:

                  server.example.com
                  username@server2.example.com
                  8/my-8-core-server.example.com
                  2/my_other_username@my-dualcore.example.net
                  # This server has SSH running on port 2222
                  ssh -p 2222 server.example.net
                  4/ssh -p 2222 quadserver.example.net
                  # Use a different ssh program
                  myssh -p 2222 -l myusername hexacpu.example.net
                  # Use a different ssh program with default number of cores
                  //usr/local/bin/myssh -p 2222 -l myusername hexacpu.example.net
                  # Use a different ssh program with 6 cores
                  6//usr/local/bin/myssh -p 2222 -l myusername hexacpu.example.net
                  # Assume 16 cores on the local computer
                  16/:

                When using a different ssh program the last argument must be
                the hostname.

                Multiple --sshloginfile are allowed.

                The sshloginfile '..' is special, it read sshlogins from
                ~/.parallel/sshloginfile

                The sshloginfile '.' is special, it read sshlogins from
                /etc/parallel/sshloginfile

                The sshloginfile '-' is special, too, it read sshlogins from
                stdin (standard input).

       --noswap Do not start new jobs on a given computer if there is both
                swap-in and swap-out activity.

                The swap activity is only sampled every 10 seconds as the
                sampling takes 1 second to do.

                Swap activity is computed as (swap-in)*(swap-out) which in
                practice is a good value: swapping out is not a problem,
                swapping in is not a problem, but both swapping in and out
                usually indicates a problem.

       --silent Silent.  The job to be run will not be printed. This is the
                default.  Can be reversed with -v.

       --tty    Open terminal tty. If GNU parallel is used for starting an
                interactive program then this option may be needed. It will
                start only one job at a time (i.e. -j1), not buffer the output
                (i.e. -u), and it will open a tty for the job. When the job is
                done, the next job will get the tty.

       --tag    Tag lines with arguments. Each output line will be prepended
                with the arguments and TAB (\t). When combined with --onall or
                --nonall the lines will be prepended with the sshlogin
                instead.

                --tag is ignored when using -u.

       --tagstring str
                Tag lines with a string. Each output line will be prepended
                with str and TAB (\t). str can contain replacement strings
                such as {}.

                --tagstring is ignored when using -u, --onall, and --nonall.

       --tmpdir dirname
                Directory for temporary files. GNU parallel normally buffers
                output into temporary files in /tmp. By setting --tmpdir you
                can use a different dir for the files. Setting --tmpdir is
                equivalent to setting $TMPDIR.

       --timeout sec
                Time out for command. If the command runs for longer than sec
                seconds it will get killed with SIGTERM, followed by SIGTERM
                200 ms later, followed by SIGKILL 200 ms later.

       --tollef Make GNU parallel behave more like Tollef's parallel command.
                It activates -u, -q, and --arg-sep --. It also causes -l to
                change meaning to --load.

                Not giving '--' is unsupported.

                Do not use --tollef unless you know what you are doing.

                To override use --gnu.

       --verbose
       -t       Print the job to be run on stderr (standard error).

                See also -v and -p.

       --transfer
                Transfer files to remote computers. --transfer is used with
                --sshlogin when the arguments are files and should be
                transferred to the remote computers. The files will be
                transferred using rsync and will be put relative to the
                default login dir. E.g.

                  echo foo/bar.txt | parallel \
                    --sshlogin server.example.com --transfer wc

                This will transfer the file foo/bar.txt to the computer
                server.example.com to the file $HOME/foo/bar.txt before
                running wc foo/bar.txt on server.example.com.

                  echo /tmp/foo/bar.txt | parallel \
                    --sshlogin server.example.com --transfer wc

                This will transfer the file foo/bar.txt to the computer
                server.example.com to the file /tmp/foo/bar.txt before running
                wc /tmp/foo/bar.txt on server.example.com.

                --transfer is often used with --return and --cleanup.

                --transfer is ignored when used with --sshlogin : or when not
                used with --sshlogin.

       --trc filename
                Transfer, Return, Cleanup. Short hand for:

                --transfer --return filename --cleanup

       --trim <n|l|r|lr|rl>
                Trim white space in input.

                n   No trim. Input is not modified. This is the default.

                l   Left trim. Remove white space from start of input. E.g. "
                    a bc " -> "a bc ".

                r   Right trim. Remove white space from end of input. E.g. " a
                    bc " -> " a bc".

                lr
                rl  Both trim. Remove white space from both start and end of
                    input. E.g. " a bc " -> "a bc". This is the default if
                    --colsep is used.

       --ungroup
       -u       Ungroup output.  Output is printed as soon as possible and by
                passes GNU parallel internal processing. This may cause output
                from different commands to be mixed thus should only be used
                if you do not care about the output. Compare these:

                parallel -j0 'sleep {};echo -n start{};sleep {};echo {}end'
                ::: 1 2 3 4

                parallel -u -j0 'sleep {};echo -n start{};sleep {};echo {}end'
                ::: 1 2 3 4

                It also disables --tag. GNU parallel runs faster with -u. Can
                be reversed with --group.

       --extensionreplace replace-str
       --er replace-str
                Use the replacement string replace-str instead of {.} for
                input line without extension.

       --use-cpus-instead-of-cores
                Count the number of physical CPUs instead of CPU cores. When
                computing how many jobs to run simultaneously relative to the
                number of CPU cores you can ask GNU parallel to instead look
                at the number of physical CPUs. This will make sense for
                computers that have hyperthreading as two jobs running on one
                CPU with hyperthreading will run slower than two jobs running
                on two physical CPUs. Some multi-core CPUs can run faster if
                only one thread is running per physical CPU. Most users will
                not need this option.

       -v       Verbose.  Print the job to be run on stdout (standard output).
                Can be reversed with --silent. See also -t.

                Use -v -v to print the wrapping ssh command when running
                remotely.

       --version
       -V       Print the version GNU parallel and exit.

       --workdir mydir
       --wd mydir
                Files transferred using --transfer and --return will be
                relative to mydir on remote computers, and the command will be
                executed in the dir mydir.

                The special mydir value ... will create working dirs under
                ~/.parallel/tmp/ on the remote computers. If --cleanup is
                given these dirs will be removed.

                The special mydir value . uses the current working dir.  If
                the current working dir is beneath your home dir, the value .
                is treated as the relative path to your home dir. This means
                that if your home dir is different on remote computers (e.g.
                if your login is different) the relative path will still be
                relative to your home dir.

       --wait   Wait for all commands to complete.

                Implies --semaphore.

                See also: man sem

       -X       Multiple arguments with context replace. Insert as many
                arguments as the command line length permits. If multiple jobs
                are being run in parallel: distribute the arguments evenly
                among the jobs. Use -j1 to avoid this.

                If {} is not used the arguments will be appended to the line.
                If {} is used as part of a word (like pic{}.jpg) then the
                whole word will be repeated. If {} is used multiple times each
                {} will be replaced with the arguments.

                Normally -X will do the right thing, whereas -m can give
                unexpected results if {} is used as part of a word.

                Support for -X with --sshlogin is limited and may fail.

                See also -m.

       --exit
       -x       Exit if the size (see the -s option) is exceeded.

       --xapply Read multiple input sources like xapply. If multiple input
                sources are given, one argument will be read from each of the
                input sources. The arguments can be accessed in the command as
                {1} .. {n}, so {1} will be a line from the first input source,
                and {6} will refer to the line with the same line number from
                the 6th input source.

                Compare these two:

                  parallel echo {1} {2} ::: 1 2 3 ::: a b c
                  parallel --xapply echo {1} {2} ::: 1 2 3 ::: a b c

                See also --header.

       --shebang
       --hashbang
                GNU Parallel can be called as a shebang (#!) command as the
                first line of a script. Like this:

                  #!/usr/bin/parallel --shebang -r traceroute

                  foss.org.my
                  debian.org
                  freenetproject.org

                For this to work --shebang must be set as the first option.

EXAMPLE: Working as xargs -n1. Argument appending
       GNU parallel can work similar to xargs -n1.

       To compress all html files using gzip run:

       find . -name '*.html' | parallel gzip

       If the file names may contain a newline use -0. Substitute FOO BAR with
       FUBAR in all files in this dir and subdirs:

       find . -type f -print0 | parallel -q0 perl -i -pe 's/FOO BAR/FUBAR/g'

       Note -q is needed because of the space in 'FOO BAR'.

EXAMPLE: Reading arguments from command line
       GNU parallel can take the arguments from command line instead of stdin
       (standard input). To compress all html files in the current dir using
       gzip run:

       parallel gzip ::: *.html

       To convert *.wav to *.mp3 using LAME running one process per CPU core
       run:

       parallel lame {} -o {.}.mp3 ::: *.wav

EXAMPLE: Inserting multiple arguments
       When moving a lot of files like this: mv *.log destdir you will
       sometimes get the error:

       bash: /bin/mv: Argument list too long

       because there are too many files. You can instead do:

       ls | grep -E '\.log$' | parallel mv {} destdir

       This will run mv for each file. It can be done faster if mv gets as
       many arguments that will fit on the line:

       ls | grep -E '\.log$' | parallel -m mv {} destdir

EXAMPLE: Context replace
       To remove the files pict0000.jpg .. pict9999.jpg you could do:

       seq -w 0 9999 | parallel rm pict{}.jpg

       You could also do:

       seq -w 0 9999 | perl -pe 's/(.*)/pict$1.jpg/' | parallel -m rm

       The first will run rm 10000 times, while the last will only run rm as
       many times needed to keep the command line length short enough to avoid
       Argument list too long (it typically runs 1-2 times).

       You could also run:

       seq -w 0 9999 | parallel -X rm pict{}.jpg

       This will also only run rm as many times needed to keep the command
       line length short enough.

EXAMPLE: Compute intensive jobs and substitution
       If ImageMagick is installed this will generate a thumbnail of a jpg
       file:

       convert -geometry 120 foo.jpg thumb_foo.jpg

       This will run with number-of-cpu-cores jobs in parallel for all jpg
       files in a directory:

       ls *.jpg | parallel convert -geometry 120 {} thumb_{}

       To do it recursively use find:

       find . -name '*.jpg' | parallel convert -geometry 120 {} {}_thumb.jpg

       Notice how the argument has to start with {} as {} will include path
       (e.g. running convert -geometry 120 ./foo/bar.jpg thumb_./foo/bar.jpg
       would clearly be wrong). The command will generate files like
       ./foo/bar.jpg_thumb.jpg.

       Use {.} to avoid the extra .jpg in the file name. This command will
       make files like ./foo/bar_thumb.jpg:

       find . -name '*.jpg' | parallel convert -geometry 120 {} {.}_thumb.jpg

EXAMPLE: Substitution and redirection
       This will generate an uncompressed version of .gz-files next to the
       .gz-file:

       parallel zcat {} ">"{.} ::: *.gz

       Quoting of > is necessary to postpone the redirection. Another solution
       is to quote the whole command:

       parallel "zcat {} >{.}" ::: *.gz

       Other special shell characters (such as * ; $ > < | >> <<) also need to
       be put in quotes, as they may otherwise be interpreted by the shell and
       not given to GNU parallel.

EXAMPLE: Composed commands
       A job can consist of several commands. This will print the number of
       files in each directory:

       ls | parallel 'echo -n {}" "; ls {}|wc -l'

       To put the output in a file called <name>.dir:

       ls | parallel '(echo -n {}" "; ls {}|wc -l) > {}.dir'

       Even small shell scripts can be run by GNU parallel:

       find . | parallel 'a={}; name=${a##*/}; upper=$(echo "$name" | tr
       "[:lower:]" "[:upper:]"); echo "$name - $upper"'

       ls | parallel 'mv {} "$(echo {} | tr "[:upper:]" "[:lower:]")"'

       Given a list of URLs, list all URLs that fail to download. Print the
       line number and the URL.

       cat urlfile | parallel "wget {} 2>/dev/null || grep -n {} urlfile"

       Create a mirror directory with the same filenames except all files and
       symlinks are empty files.

       cp -rs /the/source/dir mirror_dir; find mirror_dir -type l | parallel
       -m rm {} '&&' touch {}

       Find the files in a list that do not exist

       cat file_list | parallel 'if [ ! -e {} ] ; then echo {}; fi'

EXAMPLE: Removing file extension when processing files
       When processing files removing the file extension using {.} is often
       useful.

       Create a directory for each zip-file and unzip it in that dir:

       parallel 'mkdir {.}; cd {.}; unzip ../{}' ::: *.zip

       Recompress all .gz files in current directory using bzip2 running 1 job
       per CPU core in parallel:

       parallel "zcat {} | bzip2 >{.}.bz2 && rm {}" ::: *.gz

       Convert all WAV files to MP3 using LAME:

       find sounddir -type f -name '*.wav' | parallel lame {} -o {.}.mp3

       Put all converted in the same directory:

       find sounddir -type f -name '*.wav' | parallel lame {} -o
       mydir/{/.}.mp3

EXAMPLE: Removing two file extensions when processing files and calling GNU
       Parallel from itself
       If you have directory with tar.gz files and want these extracted in the
       corresponding dir (e.g foo.tar.gz will be extracted in the dir foo) you
       can do:

       ls *.tar.gz| parallel --er {tar} 'echo {tar}|parallel "mkdir -p {.} ;
       tar -C {.} -xf {.}.tar.gz"'

EXAMPLE: Download 10 images for each of the past 30 days
       Let us assume a website stores images like:

          http://www.example.com/path/to/YYYYMMDD_##.jpg

       where YYYYMMDD is the date and ## is the number 01-10. This will
       download images for the past 30 days:

       parallel wget http://www.example.com/path/to/'$(date -d "today -{1}
       days" +%Y%m%d)_{2}.jpg' ::: $(seq 30) ::: $(seq -w 10)

       $(date -d "today -{1} days" +%Y%m%d) will give the dates in YYYYMMDD
       with {1} days subtracted.

EXAMPLE: Breadth first parallel web crawler/mirrorer
       This script below will crawl and mirror a URL in parallel.  It
       downloads first pages that are 1 click down, then 2 clicks down, then
       3; instead of the normal depth first, where the first link link on each
       page is fetched first.

       Run like this:

       PARALLEL=-j100 ./parallel-crawl http://gatt.org.yeslab.org/

       Remove the wget part if you only want a web crawler.

       It works by fetching a page from a list of URLs and looking for links
       in that page that are within the same starting URL and that have not
       already been seen. These links are added to a new queue. When all the
       pages from the list is done, the new queue is moved to the list of URLs
       and the process is started over until no unseen links are found.

         #!/bin/bash

         # E.g. http://gatt.org.yeslab.org/
         URL=$1
         # Stay inside the start dir
         BASEURL=$(echo $URL | perl -pe 's:#.*::; s:(//.*/)[^/]*:$1:')
         URLLIST=$(mktemp urllist.XXXX)
         URLLIST2=$(mktemp urllist.XXXX)
         SEEN=$(mktemp seen.XXXX)

         # Spider to get the URLs
         echo $URL >$URLLIST
         cp $URLLIST $SEEN

         while [ -s $URLLIST ] ; do
           cat $URLLIST |
             parallel lynx -listonly -image_links -dump {} \; wget -qm -l1 -Q1 {} \; echo Spidered: {} \>\&2 |
             perl -ne 's/#.*//; s/\s+\d+.\s(\S+)$/$1/ and do { $seen{$1}++ or print }' |
             grep -F $BASEURL |
             grep -v -x -F -f $SEEN | tee -a $SEEN > $URLLIST2
           mv $URLLIST2 $URLLIST
         done

         rm -f $URLLIST $URLLIST2 $SEEN

EXAMPLE: Process files from a tar file while unpacking
       If the files to be processed are in a tar file then unpacking one file
       and processing it immediately may be faster than first unpacking all
       files.

       tar xvf foo.tgz | perl -ne 'print $l;$l=$_;END{print $l}' | parallel
       echo

       The Perl one-liner is needed to avoid race condition.

EXAMPLE: Rewriting a for-loop and a while-read-loop
       for-loops like this:

         (for x in `cat list` ; do
           do_something $x
         done) | process_output

       and while-read-loops like this:

         cat list | (while read x ; do
           do_something $x
         done) | process_output

       can be written like this:

       cat list | parallel do_something | process_output

       If the processing requires more steps the for-loop like this:

        (for x in `cat list` ; do
          no_extension=${x%.*};
          do_something $x scale $no_extension.jpg
          do_step2 <$x $no_extension
        done) | process_output

       and while-loops like this:

        cat list | (while read x ; do
          no_extension=${x%.*};
          do_something $x scale $no_extension.jpg
          do_step2 <$x $no_extension
        done) | process_output

       can be written like this:

       cat list | parallel "do_something {} scale {.}.jpg ; do_step2 <{} {.}"
       | process_output

EXAMPLE: Rewriting nested for-loops
       Nested for-loops like this:

         (for x in `cat xlist` ; do
           for y in `cat ylist` ; do
             do_something $x $y
           done
         done) | process_output

       can be written like this:

       parallel do_something {1} {2} :::: xlist ylist | process_output

       Nested for-loops like this:

         (for gender in M F ; do
           for size in S M L XL XXL ; do
             echo $gender $size
           done
         done) | sort

       can be written like this:

       parallel echo {1} {2} ::: M F ::: S M L XL XXL | sort

EXAMPLE: for-loops with column names
       When doing multiple nested for-loops it can be easier to keep track of
       the loop variable if is is named instead of just having a number. Use
       --header : to let the first argument be an named alias for the
       positional replacement string:

         parallel --header : echo {gender} {size} ::: gender M F ::: size S M L XL XXL

       This also works if the input file is a file with columns:

         cat addressbook.tsv | parallel --colsep '\t' --header : echo {Name} {E-mail address}

EXAMPLE: Count the differences between all files in a dir
       Using --results the results are saved in /tmp/diffcount*.

         parallel --results /tmp/diffcount "diff -U 0 {1} {2} |tail -n +3 |grep -v '^@'|wc -l" ::: * ::: *

       To see the difference between file A and file B look at the file
       '/tmp/diffcount 1 A 2 B' where spaces are TABs (\t).

EXAMPLE: Speeding up fast jobs
       Starting a job on the local machine takes around 3 ms. This can be a
       big overhead if the job takes very few ms to run. Often you can group
       small jobs together using -X which will make the overhead less
       significant. Compare the speed of these:

           seq -w 0 9999 | parallel touch pict{}.jpg

           seq -w 0 9999 | parallel -X touch pict{}.jpg

       If your program cannot take multiple arguments, then you can use GNU
       parallel to spawn multiple GNU parallels:

           seq -w 0 999999 | parallel -j10 --pipe parallel -j0 touch pict{}.jpg

       If -j0 normally spawns 506 jobs, then the above will try to spawn 5060
       jobs. It is likely that you this way will hit the limit of number of
       processes and/or filehandles. Look at 'ulimit -n' and 'ulimit -u' to
       raise these limits.

EXAMPLE: Using shell variables
       When using shell variables you need to quote them correctly as they may
       otherwise be split on spaces.

       Notice the difference between:

        V=("My brother's 12\" records are worth <\$\$\$>"'!' Foo Bar)
        parallel echo ::: ${V[@]} # This is probably not what you want

       and:

        V=("My brother's 12\" records are worth <\$\$\$>"'!' Foo Bar)
        parallel echo ::: "${V[@]}"

       When using variables in the actual command that contains special
       characters (e.g. space) you can quote them using '"$VAR"' or using "'s
       and -q:

        V="Here  are  two "
        parallel echo "'$V'" ::: spaces
        parallel -q echo "$V" ::: spaces

EXAMPLE: Group output lines
       When running jobs that output data, you often do not want the output of
       multiple jobs to run together. GNU parallel defaults to grouping the
       output of each job, so the output is printed when the job finishes. If
       you want the output to be printed while the job is running you can use
       -u.

       Compare the output of:

       parallel traceroute ::: foss.org.my debian.org freenetproject.org

       to the output of:

       parallel -u traceroute ::: foss.org.my debian.org freenetproject.org

EXAMPLE: Tag output lines
       GNU parallel groups the output lines, but it can be hard to see where
       the different jobs begin. --tag prepends the argument to make that more
       visible:

       parallel --tag traceroute ::: foss.org.my debian.org freenetproject.org

       Check the uptime of the servers in ~/.parallel/sshloginfile:

       parallel --tag -S .. --nonall uptime

EXAMPLE: Keep order of output same as order of input
       Normally the output of a job will be printed as soon as it completes.
       Sometimes you want the order of the output to remain the same as the
       order of the input. This is often important, if the output is used as
       input for another system. -k will make sure the order of output will be
       in the same order as input even if later jobs end before earlier jobs.

       Append a string to every line in a text file:

       cat textfile | parallel -k echo {} append_string

       If you remove -k some of the lines may come out in the wrong order.

       Another example is traceroute:

       parallel traceroute ::: foss.org.my debian.org freenetproject.org

       will give traceroute of foss.org.my, debian.org and freenetproject.org,
       but it will be sorted according to which job completed first.

       To keep the order the same as input run:

       parallel -k traceroute ::: foss.org.my debian.org freenetproject.org

       This will make sure the traceroute to foss.org.my will be printed
       first.

       A bit more complex example is downloading a huge file in chunks in
       parallel: Some internet connections will deliver more data if you
       download files in parallel. For downloading files in parallel see:
       "EXAMPLE: Download 10 images for each of the past 30 days". But if you
       are downloading a big file you can download the file in chunks in
       parallel.

       To download byte 10000000-19999999 you can use curl:

       curl -r 10000000-19999999 http://example.com/the/big/file > file.part

       To download a 1 GB file we need 100 10MB chunks downloaded and combined
       in the correct order.

       seq 0 99 | parallel -k curl -r \
           {}0000000-{}9999999 http://example.com/the/big/file > file

EXAMPLE: Parallel grep
       grep -r greps recursively through directories. On multicore CPUs GNU
       parallel can often speed this up.

       find . -type f | parallel -k -j150% -n 1000 -m grep -H -n STRING {}

       This will run 1.5 job per core, and give 1000 arguments to grep.

       To grep a big file in parallel use --pipe:

       cat bigfile | parallel --pipe grep foo

       Depending on your disks and CPUs it may be faster to read larger
       blocks:

       cat bigfile | parallel --pipe --block 10M grep foo

EXAMPLE: Using remote computers
       To run commands on a remote computer SSH needs to be set up and you
       must be able to login without entering a password (The commands ssh-
       copy-id and ssh-agent may help you do that).

       To run echo on server.example.com:

         seq 10 | parallel --sshlogin server.example.com echo

       To run commands on more than one remote computer run:

         seq 10 | parallel --sshlogin server.example.com,server2.example.net echo

       Or:

         seq 10 | parallel --sshlogin server.example.com \
           --sshlogin server2.example.net echo

       If the login username is foo on server2.example.net use:

         seq 10 | parallel --sshlogin server.example.com \
           --sshlogin foo@server2.example.net echo

       To distribute the commands to a list of computers, make a file
       mycomputers with all the computers:

         server.example.com
         foo@server2.example.com
         server3.example.com

       Then run:

         seq 10 | parallel --sshloginfile mycomputers echo

       To include the local computer add the special sshlogin ':' to the list:

         server.example.com
         foo@server2.example.com
         server3.example.com
         :

       GNU parallel will try to determine the number of CPU cores on each of
       the remote computers, and run one job per CPU core - even if the remote
       computers do not have the same number of CPU cores.

       If the number of CPU cores on the remote computers is not identified
       correctly the number of CPU cores can be added in front. Here the
       computer has 8 CPU cores.

         seq 10 | parallel --sshlogin 8/server.example.com echo

EXAMPLE: Transferring of files
       To recompress gzipped files with bzip2 using a remote computer run:

         find logs/ -name '*.gz' | \
           parallel --sshlogin server.example.com \
           --transfer "zcat {} | bzip2 -9 >{.}.bz2"

       This will list the .gz-files in the logs directory and all directories
       below. Then it will transfer the files to server.example.com to the
       corresponding directory in $HOME/logs. On server.example.com the file
       will be recompressed using zcat and bzip2 resulting in the
       corresponding file with .gz replaced with .bz2.

       If you want the resulting bz2-file to be transferred back to the local
       computer add --return {.}.bz2:

         find logs/ -name '*.gz' | \
           parallel --sshlogin server.example.com \
           --transfer --return {.}.bz2 "zcat {} | bzip2 -9 >{.}.bz2"

       After the recompressing is done the .bz2-file is transferred back to
       the local computer and put next to the original .gz-file.

       If you want to delete the transferred files on the remote computer add
       --cleanup. This will remove both the file transferred to the remote
       computer and the files transferred from the remote computer:

         find logs/ -name '*.gz' | \
           parallel --sshlogin server.example.com \
           --transfer --return {.}.bz2 --cleanup "zcat {} | bzip2 -9 >{.}.bz2"

       If you want run on several computers add the computers to --sshlogin
       either using ',' or multiple --sshlogin:

         find logs/ -name '*.gz' | \
           parallel --sshlogin server.example.com,server2.example.com \
           --sshlogin server3.example.com \
           --transfer --return {.}.bz2 --cleanup "zcat {} | bzip2 -9 >{.}.bz2"

       You can add the local computer using --sshlogin :. This will disable
       the removing and transferring for the local computer only:

         find logs/ -name '*.gz' | \
           parallel --sshlogin server.example.com,server2.example.com \
           --sshlogin server3.example.com \
           --sshlogin : \
           --transfer --return {.}.bz2 --cleanup "zcat {} | bzip2 -9 >{.}.bz2"

       Often --transfer, --return and --cleanup are used together. They can be
       shortened to --trc:

         find logs/ -name '*.gz' | \
           parallel --sshlogin server.example.com,server2.example.com \
           --sshlogin server3.example.com \
           --sshlogin : \
           --trc {.}.bz2 "zcat {} | bzip2 -9 >{.}.bz2"

       With the file mycomputers containing the list of computers it becomes:

         find logs/ -name '*.gz' | parallel --sshloginfile mycomputers \
           --trc {.}.bz2 "zcat {} | bzip2 -9 >{.}.bz2"

       If the file ~/.parallel/sshloginfile contains the list of computers the
       special short hand -S .. can be used:

         find logs/ -name '*.gz' | parallel -S .. \
           --trc {.}.bz2 "zcat {} | bzip2 -9 >{.}.bz2"

EXAMPLE: Distributing work to local and remote computers
       Convert *.mp3 to *.ogg running one process per CPU core on local
       computer and server2:

         parallel --trc {.}.ogg -S server2,: \
         'mpg321 -w - {} | oggenc -q0 - -o {.}.ogg' ::: *.mp3

EXAMPLE: Running the same command on remote computers
       To run the command uptime on remote computers you can do:

       parallel --tag --nonall -S server1,server2 uptime

       --nonall reads no arguments. If you have a list of jobs you want run on
       each computer you can do:

       parallel --tag --onall -S server1,server2 echo ::: 1 2 3

       Remove --tag if you do not want the sshlogin added before the output.

       If you have a lot of hosts use '-j0' to access more hosts in parallel.

EXAMPLE: Parallelizing rsync
       rsync is a great tool, but sometimes it will not fill up the available
       bandwidth. This is often a problem when copying several big files over
       high speed connections.

       The following will start one rsync per big file in src-dir to dest-dir
       on the server fooserver:

       find src-dir -type f -size +100000 | parallel -v ssh fooserver mkdir -p
       /dest-dir/{//}\;rsync -Havessh {} fooserver:/dest-dir/{}

       The dirs created may end up with wrong permissions and smaller files
       are not being transferred. To fix those run rsync a final time:

       rsync -Havessh src-dir/ fooserver:/dest-dir/

EXAMPLE: Use multiple inputs in one command
       Copy files like foo.es.ext to foo.ext:

       ls *.es.* | perl -pe 'print; s/\.es//' | parallel -N2 cp {1} {2}

       The perl command spits out 2 lines for each input. GNU parallel takes 2
       inputs (using -N2) and replaces {1} and {2} with the inputs.

       Count in binary:

       parallel -k echo ::: 0 1 ::: 0 1 ::: 0 1 ::: 0 1 ::: 0 1 ::: 0 1

       Print the number on the opposing sides of a six sided die:

       parallel --xapply -a <(seq 6) -a <(seq 6 -1 1) echo

       parallel --xapply echo :::: <(seq 6) <(seq 6 -1 1)

       Convert files from all subdirs to PNG-files with consecutive numbers
       (useful for making input PNG's for ffmpeg):

       parallel --xapply -a <(find . -type f | sort) -a <(seq $(find . -type
       f|wc -l)) convert {1} {2}.png

       Alternative version:

       find . -type f | sort | parallel convert {} {#}.png

EXAMPLE: Use a table as input
       Content of table_file.tsv:

         foo<TAB>bar
         baz <TAB> quux

       To run:

         cmd -o bar -i foo
         cmd -o quux -i baz

       you can run:

       parallel -a table_file.tsv --colsep '\t' cmd -o {2} -i {1}

       Note: The default for GNU parallel is to remove the spaces around the
       columns. To keep the spaces:

       parallel -a table_file.tsv --trim n --colsep '\t' cmd -o {2} -i {1}

EXAMPLE: Run the same command 10 times
       If you want to run the same command with the same arguments 10 times in
       parallel you can do:

       seq 10 | parallel -n0 my_command my_args

EXAMPLE: Working as cat | sh. Resource inexpensive jobs and evaluation
       GNU parallel can work similar to cat | sh.

       A resource inexpensive job is a job that takes very little CPU, disk
       I/O and network I/O. Ping is an example of a resource inexpensive job.
       wget is too - if the webpages are small.

       The content of the file jobs_to_run:

         ping -c 1 10.0.0.1
         wget http://example.com/status.cgi?ip=10.0.0.1
         ping -c 1 10.0.0.2
         wget http://example.com/status.cgi?ip=10.0.0.2
         ...
         ping -c 1 10.0.0.255
         wget http://example.com/status.cgi?ip=10.0.0.255

       To run 100 processes simultaneously do:

       parallel -j 100 < jobs_to_run

       As there is not a command the jobs will be evaluated by the shell.

EXAMPLE: Processing a big file using more cores
       To process a big file or some output you can use --pipe to split up the
       data into blocks and pipe the blocks into the processing program.

       If the program is gzip -9 you can do:

       cat bigfile | parallel --pipe --recend '' -k gzip -9 >bigfile.gz

       This will split bigfile into blocks of 1 MB and pass that to gzip -9 in
       parallel. One gzip will be run per CPU core. The output of gzip -9 will
       be kept in order and saved to bigfile.gz

       gzip works fine if the output is appended, but some processing does not
       work like that - for example sorting. For this GNU parallel can put the
       output of each command into a file. This will sort a big file in
       parallel:

       cat bigfile | parallel --pipe --files sort | parallel -Xj1 sort -m {}
       ';' rm {} >bigfile.sort

       Here bigfile is split into blocks of around 1MB, each block ending in
       '\n' (which is the default for --recend). Each block is passed to sort
       and the output from sort is saved into files. These files are passed to
       the second parallel that runs sort -m on the files before it removes
       the files. The output is saved to bigfile.sort.

EXAMPLE: Working as mutex and counting semaphore
       The command sem is an alias for parallel --semaphore.

       A counting semaphore will allow a given number of jobs to be started in
       the background.  When the number of jobs are running in the background,
       GNU sem will wait for one of these to complete before starting another
       command. sem --wait will wait for all jobs to complete.

       Run 10 jobs concurrently in the background:

         for i in *.log ; do
           echo $i
           sem -j10 gzip $i ";" echo done
         done
         sem --wait

       A mutex is a counting semaphore allowing only one job to run. This will
       edit the file myfile and prepends the file with lines with the numbers
       1 to 3.

         seq 3 | parallel sem sed -i -e 'i{}' myfile

       As myfile can be very big it is important only one process edits the
       file at the same time.

       Name the semaphore to have multiple different semaphores active at the
       same time:

         seq 3 | parallel sem --id mymutex sed -i -e 'i{}' myfile

EXAMPLE: Start editor with filenames from stdin (standard input)
       You can use GNU parallel to start interactive programs like emacs or
       vi:

       cat filelist | parallel --tty -X emacs

       cat filelist | parallel --tty -X vi

       If there are more files than will fit on a single command line, the
       editor will be started again with the remaining files.

EXAMPLE: Running sudo
       sudo requires a password to run a command as root. It caches the
       access, so you only need to enter the password again if you have not
       used sudo for a while.

       The command:

         parallel sudo echo ::: This is a bad idea

       is no good, as you would be prompted for the sudo password for each of
       the jobs. You can either do:

         sudo echo This
         parallel sudo echo ::: is a good idea

       or:

         sudo parallel echo ::: This is a good idea

       This way you only have to enter the sudo password once.

EXAMPLE: GNU Parallel as queue system/batch manager
       GNU parallel can work as a simple job queue system or batch manager.
       The idea is to put the jobs into a file and have GNU parallel read from
       that continuously. As GNU parallel will stop at end of file we use tail
       to continue reading:

       true >jobqueue; tail -f jobqueue | parallel

       To submit your jobs to the queue:

       echo my_command my_arg >> jobqueue

       You can of course use -S to distribute the jobs to remote computers:

       echo >jobqueue; tail -f jobqueue | parallel -S ..

       There are a two small issues when using GNU parallel as queue
       system/batch manager:

       o You will get a warning if you do not submit JobSlots jobs within the
         first second. E.g. if you have 8 cores and use -j+2 you have to
         submit 10 jobs. These can be dummy jobs (e.g. echo foo). You can also
         simply ignore the warning.

       o Jobs will be run immediately, but output from jobs will only be
         printed when JobSlots more jobs has been started. E.g. if you have 10
         jobslots then the output from the first completed job will only be
         printed when job 11 is started.

EXAMPLE: GNU Parallel as dir processor
       If you have a dir in which users drop files that needs to be processed
       you can do this on GNU/Linux (If you know what inotifywait is called on
       other platforms file a bug report):

       inotifywait -q -m -r -e MOVED_TO -e CLOSE_WRITE --format %w%f my_dir |
       parallel -u echo

       This will run the command echo on each file put into my_dir or subdirs
       of my_dir.

       The -u is needed because of a small bug in GNU parallel. If that proves
       to be a problem, file a bug report.

       You can of course use -S to distribute the jobs to remote computers:

       inotifywait -q -m -r -e MOVED_TO -e CLOSE_WRITE --format %w%f my_dir |
       parallel -S ..  -u echo

       If the files to be processed are in a tar file then unpacking one file
       and processing it immediately may be faster than first unpacking all
       files. Set up the dir processor as above and unpack into the dir.

QUOTING
       GNU parallel is very liberal in quoting. You only need to quote
       characters that have special meaning in shell:

       ( ) $ ` ' " < > ; | \

       and depending on context these needs to be quoted, too:

       ~ & # ! ? space * {

       Therefore most people will never need more quoting than putting '\' in
       front of the special characters.

       Often you can simply put \' around every ':

         perl -ne '/^\S+\s+\S+$/ and print $ARGV,"\n"' file

       can be quoted:

         parallel perl -ne \''/^\S+\s+\S+$/ and print $ARGV,"\n"'\' ::: file

       However, when you want to use a shell variable you need to quote the
       $-sign. Here is an example using $PARALLEL_SEQ. This variable is set by
       GNU parallel itself, so the evaluation of the $ must be done by the sub
       shell started by GNU parallel:

       seq 10 | parallel -N2 echo seq:\$PARALLEL_SEQ arg1:{1} arg2:{2}

       If the variable is set before GNU parallel starts you can do this:

       VAR=this_is_set_before_starting

       echo test | parallel echo {} $VAR

       Prints: test this_is_set_before_starting

       It is a little more tricky if the variable contains more than one space
       in a row:

       VAR="two  spaces  between  each  word"

       echo test | parallel echo {} \'"$VAR"\'

       Prints: test two  spaces  between  each  word

       If the variable should not be evaluated by the shell starting GNU
       parallel but be evaluated by the sub shell started by GNU parallel,
       then you need to quote it:

       echo test | parallel VAR=this_is_set_after_starting \; echo {} \$VAR

       Prints: test this_is_set_after_starting

       It is a little more tricky if the variable contains space:

       echo test | parallel VAR='"two  spaces  between  each  word"' echo {}
       \'"$VAR"\'

       Prints: test two  spaces  between  each  word

       $$ is the shell variable containing the process id of the shell. This
       will print the process id of the shell running GNU parallel:

       seq 10 | parallel echo $$

       And this will print the process ids of the sub shells started by GNU
       parallel.

       seq 10 | parallel echo \$\$

       If the special characters should not be evaluated by the sub shell then
       you need to protect it against evaluation from both the shell starting
       GNU parallel and the sub shell:

       echo test | parallel echo {} \\\$VAR

       Prints: test $VAR

       GNU parallel can protect against evaluation by the sub shell by using
       -q:

       echo test | parallel -q echo {} \$VAR

       Prints: test $VAR

       This is particularly useful if you have lots of quoting. If you want to
       run a perl script like this:

       perl -ne '/^\S+\s+\S+$/ and print $ARGV,"\n"' file

       It needs to be quoted like this:

       ls | parallel  perl -ne '/^\\S+\\s+\\S+\$/\ and\ print\ \$ARGV,\"\\n\"'

       Notice how spaces, \'s, "'s, and $'s need to be quoted. GNU parallel
       can do the quoting by using option -q:

       ls | parallel -q  perl -ne '/^\S+\s+\S+$/ and print $ARGV,"\n"'

       However, this means you cannot make the sub shell interpret special
       characters. For example because of -q this WILL NOT WORK:

       ls *.gz | parallel -q "zcat {} >{.}"

       ls *.gz | parallel -q "zcat {} | bzip2 >{.}.bz2"

       because > and | need to be interpreted by the sub shell.

       If you get errors like:

         sh: -c: line 0: syntax error near unexpected token
         sh: Syntax error: Unterminated quoted string
         sh: -c: line 0: unexpected EOF while looking for matching `''
         sh: -c: line 1: syntax error: unexpected end of file

       then you might try using -q.

       If you are using bash process substitution like <(cat foo) then you may
       try -q and prepending command with bash -c:

       ls | parallel -q bash -c 'wc -c <(echo {})'

       Or for substituting output:

       ls | parallel -q bash -c 'tar c {} | tee >(gzip >{}.tar.gz) | bzip2
       >{}.tar.bz2'

       Conclusion: To avoid dealing with the quoting problems it may be easier
       just to write a small script and have GNU parallel call that script.

LIST RUNNING JOBS
       If you want a list of the jobs currently running you can run:

       killall -USR1 parallel

       GNU parallel will then print the currently running jobs on stderr
       (standard error).

COMPLETE RUNNING JOBS BUT DO NOT START NEW JOBS
       If you regret starting a lot of jobs you can simply break GNU parallel,
       but if you want to make sure you do not have half-completed jobs you
       should send the signal SIGTERM to GNU parallel:

       killall -TERM parallel

       This will tell GNU parallel to not start any new jobs, but wait until
       the currently running jobs are finished before exiting.

ENVIRONMENT VARIABLES
       $PARALLEL_PID
                The environment variable $PARALLEL_PID is set by GNU parallel
                and is visible to the jobs started from GNU parallel. This
                makes it possible for the jobs to communicate directly to GNU
                parallel.  Remember to quote the $, so it gets evaluated by
                the correct shell.

                Example: If each of the jobs tests a solution and one of jobs
                finds the solution the job can tell GNU parallel not to start
                more jobs by: kill -TERM $PARALLEL_PID. This only works on the
                local computer.

       $PARALLEL_SEQ
                $PARALLEL_SEQ will be set to the sequence number of the job
                running. Remember to quote the $, so it gets evaluated by the
                correct shell.

                Example:

                seq 10 | parallel -N2 echo seq:'$'PARALLEL_SEQ arg1:{1}
                arg2:{2}

       $TMPDIR  Directory for temporary files. See: --tmpdir.

       $PARALLEL
                The environment variable $PARALLEL will be used as default
                options for GNU parallel. If the variable contains special
                shell characters (e.g. $, *, or space) then these need to be
                to be escaped with \.

                Example:

                cat list | parallel -j1 -k -v ls

                can be written as:

                cat list | PARALLEL="-kvj1" parallel ls

                cat list | parallel -j1 -k -v -S"myssh user@server" ls

                can be written as:

                cat list | PARALLEL='-kvj1 -S myssh\ user@server' parallel
                echo

                Notice the \ in the middle is needed because 'myssh' and
                'user@server' must be one argument.

DEFAULT PROFILE (CONFIG FILE)
       The file ~/.parallel/config (formerly known as .parallelrc) will be
       read if it exists.  Lines starting with '#' will be ignored. It can be
       formatted like the environment variable $PARALLEL, but it is often
       easier to simply put each option on its own line.

       Options on the command line takes precedence over the environment
       variable $PARALLEL which takes precedence over the file
       ~/.parallel/config.

PROFILE FILES
       If --profile set, GNU parallel will read the profile from that file
       instead of ~/.parallel/config. You can have multiple --profiles.

       Example: Profile for running a command on every sshlogin in
       ~/.ssh/sshlogins and prepend the output with the sshlogin:

         echo --tag -S .. --nonall > ~/.parallel/n
         parallel -Jn uptime

       Example: Profile for running every command with -j-1 and nice

         echo -j-1 nice > ~/.parallel/nice_profile
         parallel -J nice_profile bzip2 -9 ::: *

       Example: Profile for running a perl script before every command:

         echo "perl -e '\$a=\$\$; print \$a,\" \",'\$PARALLEL_SEQ',\" \";';" > ~/.parallel/pre_perl
         parallel -J pre_perl echo ::: *

       Note how the $ and " need to be quoted using \.

       Example: Profile for running distributed jobs with nice on the remote
       computers:

         echo -S .. nice > ~/.parallel/dist
         parallel -J dist --trc {.}.bz2 bzip2 -9 ::: *

EXIT STATUS
       If --halt-on-error 0 or not specified:

       0     All jobs ran without error.

       1-253 Some of the jobs failed. The exit status gives the number of
             failed jobs

       254   More than 253 jobs failed.

       255   Other error.

       If --halt-on-error 1 or 2: Exit status of the failing job.

DIFFERENCES BETWEEN GNU Parallel AND ALTERNATIVES
       There are a lot programs with some of the functionality of GNU
       parallel. GNU parallel strives to include the best of the functionality
       without sacrificing ease of use.

   SUMMARY TABLE
       The following features are in some of the comparable tools:

       Inputs
        I1. Arguments can be read from stdin
        I2. Arguments can be read from a file
        I3. Arguments can be read from multiple files
        I4. Arguments can be read from command line
        I5. Arguments can be read from a table
        I6. Arguments can be read from the same file using #! (shebang)
        I7. Line oriented input as default (Quoting of special chars not
       needed)

       Manipulation of input
        M1. Composed command
        M2. Multiple arguments can fill up an execution line
        M3. Arguments can be put anywhere in the execution line
        M4. Multiple arguments can be put anywhere in the execution line
        M5. Arguments can be replaced with context
        M6. Input can be treated as complete execution line

       Outputs
        O1. Grouping output so output from different jobs do not mix
        O2. Send stderr (standard error) to stderr (standard error)
        O3. Send stdout (standard output) to stdout (standard output)
        O4. Order of output can be same as order of input
        O5. Stdout only contains stdout (standard output) from the command
        O6. Stderr only contains stderr (standard error) from the command

       Execution
        E1. Running jobs in parallel
        E2. List running jobs
        E3. Finish running jobs, but do not start new jobs
        E4. Number of running jobs can depend on number of cpus
        E5. Finish running jobs, but do not start new jobs after first failure
        E6. Number of running jobs can be adjusted while running

       Remote execution
        R1. Jobs can be run on remote computers
        R2. Basefiles can be transferred
        R3. Argument files can be transferred
        R4. Result files can be transferred
        R5. Cleanup of transferred files
        R6. No config files needed
        R7. Do not run more than SSHD's MaxStartup can handle
        R8. Configurable SSH command
        R9. Retry if connection breaks occasionally

       Semaphore
        S1. Possibility to work as a mutex
        S2. Possibility to work as a counting semaphore

       Legend
        - = no
        x = not applicable
        ID = yes

       As every new version of the programs are not tested the table may be
       outdated. Please file a bug-report if you find errors (See REPORTING
       BUGS).

       parallel: I1 I2 I3 I4 I5 I6 I7 M1 M2 M3 M4 M5 M6 O1 O2 O3 O4 O5 O6 E1
       E2 E3 E4 E5 E6 R1 R2 R3 R4 R5 R6 R7 R8 R9 S1 S2

       xargs: I1 I2 -  -  -  -  - -  M2 M3 -  -  - -  O2 O3 -  O5 O6 E1 -  -
       -  -  - -  -  -  -  -  x  -  -  - -  -

       find -exec: -  -  -  x  -  x  - -  M2 M3 -  -  -  - -  O2 O3 O4 O5 O6 -
       -  -  -  -  -  - -  -  -  -  -  -  -  -  - x  x

       make -j: -  -  -  -  -  -  - -  -  -  -  -  - O1 O2 O3 -  x  O6 E1 -  -
       -  E5 - -  -  -  -  -  -  -  -  - -  -

       ppss: I1 I2 -  -  -  -  I7 M1 -  M3 -  -  M6 O1 -  -  x  -  - E1 E2 ?E3
       E4 - - R1 R2 R3 R4 -  -  ?R7 ? ?  -  -

       pexec: I1 I2 -  I4 I5 -  - M1 -  M3 -  -  M6 O1 O2 O3 -  O5 O6 E1 -  -
       E4 -  E6 R1 -  -  -  -  R6 -  -  - S1 -

       xjobs: TODO - Please file a bug-report if you know what features xjobs
       supports (See REPORTING BUGS).

       prll: TODO - Please file a bug-report if you know what features prll
       supports (See REPORTING BUGS).

       dxargs: TODO - Please file a bug-report if you know what features
       dxargs supports (See REPORTING BUGS).

       mdm/middelman: TODO - Please file a bug-report if you know what
       features mdm/middelman supports (See REPORTING BUGS).

       xapply: TODO - Please file a bug-report if you know what features
       xapply supports (See REPORTING BUGS).

       paexec: TODO - Please file a bug-report if you know what features
       paexec supports (See REPORTING BUGS).

       ClusterSSH: TODO - Please file a bug-report if you know what features
       ClusterSSH supports (See REPORTING BUGS).

   DIFFERENCES BETWEEN xargs AND GNU Parallel
       xargs offer some of the same possibilities as GNU parallel.

       xargs deals badly with special characters (such as space, ' and "). To
       see the problem try this:

         touch important_file
         touch 'not important_file'
         ls not* | xargs rm
         mkdir -p "My brother's 12\" records"
         ls | xargs rmdir

       You can specify -0 or -d "\n", but many input generators are not
       optimized for using NUL as separator but are optimized for newline as
       separator. E.g head, tail, awk, ls, echo, sed, tar -v, perl (-0 and \0
       instead of \n), locate (requires using -0), find (requires using
       -print0), grep (requires user to use -z or -Z), sort (requires using
       -z).

       So GNU parallel's newline separation can be emulated with:

       cat | xargs -d "\n" -n1 command

       xargs can run a given number of jobs in parallel, but has no support
       for running number-of-cpu-cores jobs in parallel.

       xargs has no support for grouping the output, therefore output may run
       together, e.g. the first half of a line is from one process and the
       last half of the line is from another process. The example Parallel
       grep cannot be done reliably with xargs because of this. To see this in
       action try:

         parallel perl -e '\$a=\"1{}\"x10000000\;print\ \$a,\"\\n\"' '>' {} ::: a b c d e f
         ls -l a b c d e f
         parallel -kP4 -n1 grep 1 > out.par ::: a b c d e f
         echo a b c d e f | xargs -P4 -n1 grep 1 > out.xargs-unbuf
         echo a b c d e f | xargs -P4 -n1 grep --line-buffered 1 > out.xargs-linebuf
         echo a b c d e f | xargs -n1 grep --line-buffered 1 > out.xargs-serial
         ls -l out*
         md5sum out*

       xargs has no support for keeping the order of the output, therefore if
       running jobs in parallel using xargs the output of the second job
       cannot be postponed till the first job is done.

       xargs has no support for running jobs on remote computers.

       xargs has no support for context replace, so you will have to create
       the arguments.

       If you use a replace string in xargs (-I) you can not force xargs to
       use more than one argument.

       Quoting in xargs works like -q in GNU parallel. This means composed
       commands and redirection require using bash -c.

       ls | parallel "wc {} > {}.wc"

       becomes (assuming you have 8 cores)

       ls | xargs -d "\n" -P8 -I {} bash -c "wc {} > {}.wc"

       and

       ls | parallel "echo {}; ls {}|wc"

       becomes (assuming you have 8 cores)

       ls | xargs -d "\n" -P8 -I {} bash -c "echo {}; ls {}|wc"

   DIFFERENCES BETWEEN find -exec AND GNU Parallel
       find -exec offer some of the same possibilities as GNU parallel.

       find -exec only works on files. So processing other input (such as
       hosts or URLs) will require creating these inputs as files. find -exec
       has no support for running commands in parallel.

   DIFFERENCES BETWEEN make -j AND GNU Parallel
       make -j can run jobs in parallel, but requires a crafted Makefile to do
       this. That results in extra quoting to get filename containing newline
       to work correctly.

       make -j has no support for grouping the output, therefore output may
       run together, e.g. the first half of a line is from one process and the
       last half of the line is from another process. The example Parallel
       grep cannot be done reliably with make -j because of this.

       (Very early versions of GNU parallel were coincidently implemented
       using make -j).

   DIFFERENCES BETWEEN ppss AND GNU Parallel
       ppss is also a tool for running jobs in parallel.

       The output of ppss is status information and thus not useful for using
       as input for another command. The output from the jobs are put into
       files.

       The argument replace string ($ITEM) cannot be changed. Arguments must
       be quoted - thus arguments containing special characters (space '"&!*)
       may cause problems. More than one argument is not supported. File names
       containing newlines are not processed correctly. When reading input
       from a file null cannot be used as a terminator. ppss needs to read the
       whole input file before starting any jobs.

       Output and status information is stored in ppss_dir and thus requires
       cleanup when completed. If the dir is not removed before running ppss
       again it may cause nothing to happen as ppss thinks the task is already
       done. GNU parallel will normally not need cleaning up if running
       locally and will only need cleaning up if stopped abnormally and
       running remote (--cleanup may not complete if stopped abnormally). The
       example Parallel grep would require extra postprocessing if written
       using ppss.

       For remote systems PPSS requires 3 steps: config, deploy, and start.
       GNU parallel only requires one step.

       EXAMPLES FROM ppss MANUAL

       Here are the examples from ppss's manual page with the equivalent using
       GNU parallel:

       1 ./ppss.sh standalone -d /path/to/files -c 'gzip '

       1 find /path/to/files -type f | parallel gzip

       2 ./ppss.sh standalone -d /path/to/files -c 'cp "$ITEM"
       /destination/dir '

       2 find /path/to/files -type f | parallel cp {} /destination/dir

       3 ./ppss.sh standalone -f list-of-urls.txt -c 'wget -q '

       3 parallel -a list-of-urls.txt wget -q

       4 ./ppss.sh standalone -f list-of-urls.txt -c 'wget -q "$ITEM"'

       4 parallel -a list-of-urls.txt wget -q {}

       5 ./ppss config -C config.cfg -c 'encode.sh ' -d /source/dir -m
       192.168.1.100 -u ppss -k ppss-key.key -S ./encode.sh -n nodes.txt -o
       /some/output/dir --upload --download ; ./ppss deploy -C config.cfg ;
       ./ppss start -C config

       5 # parallel does not use configs. If you want a different username put
       it in nodes.txt: user@hostname

       5 find source/dir -type f | parallel --sshloginfile nodes.txt --trc
       {.}.mp3 lame -a {} -o {.}.mp3 --preset standard --quiet

       6 ./ppss stop -C config.cfg

       6 killall -TERM parallel

       7 ./ppss pause -C config.cfg

       7 Press: CTRL-Z or killall -SIGTSTP parallel

       8 ./ppss continue -C config.cfg

       8 Enter: fg or killall -SIGCONT parallel

       9 ./ppss.sh status -C config.cfg

       9 killall -SIGUSR2 parallel

   DIFFERENCES BETWEEN pexec AND GNU Parallel
       pexec is also a tool for running jobs in parallel.

       Here are the examples from pexec's info page with the equivalent using
       GNU parallel:

       1 pexec -o sqrt-%s.dat -p "$(seq 10)" -e NUM -n 4 -c -- \
         'echo "scale=10000;sqrt($NUM)" | bc'

       1 seq 10 | parallel -j4 'echo "scale=10000;sqrt({})" | bc >
       sqrt-{}.dat'

       2 pexec -p "$(ls myfiles*.ext)" -i %s -o %s.sort -- sort

       2 ls myfiles*.ext | parallel sort {} ">{}.sort"

       3 pexec -f image.list -n auto -e B -u star.log -c -- \
         'fistar $B.fits -f 100 -F id,x,y,flux -o $B.star'

       3 parallel -a image.list \
         'fistar {}.fits -f 100 -F id,x,y,flux -o {}.star' 2>star.log

       4 pexec -r *.png -e IMG -c -o - -- \
         'convert $IMG ${IMG%.png}.jpeg ; "echo $IMG: done"'

       4 ls *.png | parallel 'convert {} {.}.jpeg; echo {}: done'

       5 pexec -r *.png -i %s -o %s.jpg -c 'pngtopnm | pnmtojpeg'

       5 ls *.png | parallel 'pngtopnm < {} | pnmtojpeg > {}.jpg'

       6 for p in *.png ; do echo ${p%.png} ; done | \
         pexec -f - -i %s.png -o %s.jpg -c 'pngtopnm | pnmtojpeg'

       6 ls *.png | parallel 'pngtopnm < {} | pnmtojpeg > {.}.jpg'

       7 LIST=$(for p in *.png ; do echo ${p%.png} ; done)
         pexec -r $LIST -i %s.png -o %s.jpg -c 'pngtopnm | pnmtojpeg'

       7 ls *.png | parallel 'pngtopnm < {} | pnmtojpeg > {.}.jpg'

       8 pexec -n 8 -r *.jpg -y unix -e IMG -c \
         'pexec -j -m blockread -d $IMG | \
         jpegtopnm | pnmscale 0.5 | pnmtojpeg | \
         pexec -j -m blockwrite -s th_$IMG'

       8 Combining GNU parallel and GNU sem.

       8 ls *jpg | parallel -j8 'sem --id blockread cat {} | jpegtopnm |' \
         'pnmscale 0.5 | pnmtojpeg | sem --id blockwrite cat > th_{}'

       8 If reading and writing is done to the same disk, this may be faster
       as only one process will be either reading or writing:

       8 ls *jpg | parallel -j8 'sem --id diskio cat {} | jpegtopnm |' \
         'pnmscale 0.5 | pnmtojpeg | sem --id diskio cat > th_{}'

   DIFFERENCES BETWEEN xjobs AND GNU Parallel
       xjobs is also a tool for running jobs in parallel. It only supports
       running jobs on your local computer.

       xjobs deals badly with special characters just like xargs. See the
       section DIFFERENCES BETWEEN xargs AND GNU Parallel.

       Here are the examples from xjobs's man page with the equivalent using
       GNU parallel:

       1 ls -1 *.zip | xjobs unzip

       1 ls *.zip | parallel unzip

       2 ls -1 *.zip | xjobs -n unzip

       2 ls *.zip | parallel unzip >/dev/null

       3 find . -name '*.bak' | xjobs gzip

       3 find . -name '*.bak' | parallel gzip

       4 ls -1 *.jar | sed 's/\(.*\)/\1 > \1.idx/' | xjobs jar tf

       4 ls *.jar | parallel jar tf {} '>' {}.idx

       5 xjobs -s script

       5 cat script | parallel

       6 mkfifo /var/run/my_named_pipe; xjobs -s /var/run/my_named_pipe & echo
       unzip 1.zip >> /var/run/my_named_pipe; echo tar cf /backup/myhome.tar
       /home/me >> /var/run/my_named_pipe

       6 mkfifo /var/run/my_named_pipe; cat /var/run/my_named_pipe | parallel
       & echo unzip 1.zip >> /var/run/my_named_pipe; echo tar cf
       /backup/myhome.tar /home/me >> /var/run/my_named_pipe

   DIFFERENCES BETWEEN prll AND GNU Parallel
       prll is also a tool for running jobs in parallel. It does not support
       running jobs on remote computers.

       prll encourages using BASH aliases and BASH functions instead of
       scripts. GNU parallel will never support running aliases (see why
       http://www.perlmonks.org/index.pl?node_id=484296). However, scripts,
       composed commands, or functions exported with export -f work just fine.

       prll generates a lot of status information on stderr (standard error)
       which makes it harder to use the stderr (standard error) output of the
       job directly as input for another program.

       Here is the example from prll's man page with the equivalent using GNU
       parallel:

       prll -s 'mogrify -flip $1' *.jpg

       parallel mogrify -flip ::: *.jpg

   DIFFERENCES BETWEEN dxargs AND GNU Parallel
       dxargs is also a tool for running jobs in parallel.

       dxargs does not deal well with more simultaneous jobs than SSHD's
       MaxStartup. dxargs is only built for remote run jobs, but does not
       support transferring of files.

   DIFFERENCES BETWEEN mdm/middleman AND GNU Parallel
       middleman(mdm) is also a tool for running jobs in parallel.

       Here are the shellscripts of http://mdm.berlios.de/usage.html ported to
       GNU parallel:

       seq 19 | parallel buffon -o - | sort -n > result

       cat files | parallel cmd

       find dir -execdir sem cmd {} \;

   DIFFERENCES BETWEEN xapply AND GNU Parallel
       xapply can run jobs in parallel on the local computer.

       Here are the examples from xapply's man page with the equivalent using
       GNU parallel:

       1 xapply '(cd %1 && make all)' */

       1 parallel 'cd {} && make all' ::: */

       2 xapply -f 'diff %1 ../version5/%1' manifest | more

       2 parallel diff {} ../version5/{} < manifest | more

       3 xapply -p/dev/null -f 'diff %1 %2' manifest1 checklist1

       3 parallel --xapply diff {1} {2} :::: manifest1 checklist1

       4 xapply 'indent' *.c

       4 parallel indent ::: *.c

       5 find ~ksb/bin -type f ! -perm -111 -print | xapply -f -v 'chmod a+x'
       -

       5 find ~ksb/bin -type f ! -perm -111 -print | parallel -v chmod a+x

       6 find */ -... | fmt 960 1024 | xapply -f -i /dev/tty 'vi' -

       6 sh <(find */ -... | parallel -s 1024 echo vi)

       6 find */ -... | parallel -s 1024 -Xuj1 vi

       7 find ... | xapply -f -5 -i /dev/tty 'vi' - - - - -

       7 sh <(find ... |parallel -n5 echo vi)

       7 find ... |parallel -n5 -uj1 vi

       8 xapply -fn "" /etc/passwd

       8 parallel -k echo < /etc/passwd

       9 tr ':' '\012' < /etc/passwd | xapply -7 -nf 'chown %1 %6' - - - - - -
       -

       9 tr ':' '\012' < /etc/passwd | parallel -N7 chown {1} {6}

       10 xapply '[ -d %1/RCS ] || echo %1' */

       10 parallel '[ -d {}/RCS ] || echo {}' ::: */

       11 xapply -f '[ -f %1 ] && echo %1' List | ...

       11 parallel '[ -f {} ] && echo {}' < List | ...

   DIFFERENCES BETWEEN paexec AND GNU Parallel
       paexec can run jobs in parallel on both the local and remote computers.

       paexec requires commands to print a blank line as the last output. This
       means you will have to write a wrapper for most programs.

       paexec has a job dependency facility so a job can depend on another job
       to be executed successfully. Sort of a poor-man's make.

       Here are the examples from paexec's example catalog with the equivalent
       using GNU parallel:

       1_div_X_run:
          ../../paexec -s -l -c "`pwd`/1_div_X_cmd" -n +1 <<EOF [...]
          parallel echo {} '|' `pwd`/1_div_X_cmd <<EOF [...]

       all_substr_run:
          ../../paexec -lp -c "`pwd`/all_substr_cmd" -n +3 <<EOF [...]
          parallel echo {} '|' `pwd`/all_substr_cmd <<EOF [...]

       cc_wrapper_run:
          ../../paexec -c "env CC=gcc CFLAGS=-O2 `pwd`/cc_wrapper_cmd" \
                     -n 'host1 host2' \
                     -t '/usr/bin/ssh -x' <<EOF [...]
          parallel echo {} '|' "env CC=gcc CFLAGS=-O2 `pwd`/cc_wrapper_cmd" \
                     -S host1,host2 <<EOF [...]
          # This is not exactly the same, but avoids the wrapper
          parallel gcc -O2 -c -o {.}.o {} \
                     -S host1,host2 <<EOF [...]

       toupper_run:
          ../../paexec -lp -c "`pwd`/toupper_cmd" -n +10 <<EOF [...]
          parallel echo {} '|' ./toupper_cmd <<EOF [...]
          # Without the wrapper:
          parallel echo {} '| awk {print\ toupper\(\$0\)}' <<EOF [...]

   DIFFERENCES BETWEEN ClusterSSH AND GNU Parallel
       ClusterSSH solves a different problem than GNU parallel.

       ClusterSSH opens a terminal window for each computer and using a master
       window you can run the same command on all the computers. This is
       typically used for administrating several computers that are almost
       identical.

       GNU parallel runs the same (or different) commands with different
       arguments in parallel possibly using remote computers to help
       computing. If more than one computer is listed in -S GNU parallel may
       only use one of these (e.g. if there are 8 jobs to be run and one
       computer has 8 cores).

       GNU parallel can be used as a poor-man's version of ClusterSSH:

       parallel --nonall -S server-a,server-b do_stuff foo bar

BUGS
   Quoting of newline
       Because of the way newline is quoted this will not work:

       echo 1,2,3 | parallel -vkd, "echo 'a{}b'"

       However, these will all work:

       echo 1,2,3 | parallel -vkd, echo a{}b

       echo 1,2,3 | parallel -vkd, "echo 'a'{}'b'"

       echo 1,2,3 | parallel -vkd, "echo 'a'"{}"'b'"

   Speed
       Startup

       GNU parallel is slow at starting up - around 250 ms. Half of the
       startup time is spent finding the maximal length of a command line.
       Setting -s will remove this part of the startup time.

       Job startup

       Starting a job on the local machine takes around 3 ms. This can be a
       big overhead if the job takes very few ms to run. Often you can group
       small jobs together using -X which will make the overhead less
       significant.

       Using --ungroup the 3 ms can be lowered to around 2 ms.

       SSH

       When using multiple computers GNU parallel opens ssh connections to
       them to figure out how many connections can be used reliably
       simultaneously (Namely SSHD's MaxStartup). This test is done for each
       host in serial, so if your --sshloginfile contains many hosts it may be
       slow.

       If your jobs are short you may see that there are fewer jobs running on
       the remove systems than expected. This is due to time spent logging in
       and out. -M may help here.

       Disk access

       A single disk can normally read data faster if it reads one file at a
       time instead of reading a lot of files in parallel, as this will avoid
       disk seeks. However, newer disk systems with multiple drives can read
       faster if reading from multiple files in parallel.

       If the jobs are of the form read-all-compute-all-write-all, so
       everything is read before anything is written, it may be faster to
       force only one disk access at the time:

         sem --id diskio cat file | compute | sem --id diskio cat > file

       If the jobs are of the form read-compute-write, so writing starts
       before all reading is done, it may be faster to force only one reader
       and writer at the time:

         sem --id read cat file | compute | sem --id write cat > file

       If the jobs are of the form read-compute-read-compute, it may be faster
       to run more jobs in parallel than the system has CPUs, as some of the
       jobs will be stuck waiting for disk access.

   --nice limits command length
       The current implementation of --nice is too pessimistic in the max
       allowed command length. It only uses a little more than half of what it
       could. This affects -X and -m. If this becomes a real problem for you
       file a bug-report.

   Aliases and functions do not work
       If you get:

       Can't exec "command": No such file or directory

       or:

       open3: exec of by command failed

       it may be because command is not known, but it could also be because
       command is an alias or a function. If it is a function you need to
       export -f the function first. An alias will, however, not work (see why
       http://www.perlmonks.org/index.pl?node_id=484296), so change your alias
       to a script.

REPORTING BUGS
       Report bugs to <bug-parallel@gnu.org> or
       https://savannah.gnu.org/bugs/?func=additem&group=parallel

       Your bug report should always include:

       o The output of parallel --version. If you are not running the latest
         released version you should specify why you believe the problem is
         not fixed in that version.

       o A complete example that others can run that shows the problem. A
         combination of seq, cat, echo, and sleep can reproduce most errors.
         If your example requires large files, see if you can make them by
         something like seq 1000000 > file.

       o The output of your example. If your problem is not easily reproduced
         by others, the output might help them figure out the problem.

       If you suspect the error is dependent on your distribution, please see
       if you can reproduce the error on one of these VirtualBox images:
       http://sourceforge.net/projects/virtualboximage/files/

       Specifying the name of your distribution is not enough as you may have
       installed software that is not in the VirtualBox images.

       If you cannot reproduce the error on any of the VirtualBox images
       above, you should assume the debugging will be done through you. That
       will put more burden on you and it is extra important you give any
       information that help.

AUTHOR
       When using GNU parallel for a publication please cite:

       O. Tange (2011): GNU Parallel - The Command-Line Power Tool, ;login:
       The USENIX Magazine, February 2011:42-47.

       Copyright (C) 2007-10-18 Ole Tange, http://ole.tange.dk

       Copyright (C) 2008,2009,2010 Ole Tange, http://ole.tange.dk

       Copyright (C) 2010,2011,2012 Ole Tange, http://ole.tange.dk and Free
       Software Foundation, Inc.

       Parts of the manual concerning xargs compatibility is inspired by the
       manual of xargs from GNU findutils 4.4.2.

LICENSE
       Copyright (C) 2007,2008,2009,2010,2011,2012 Free Software Foundation,
       Inc.

       This program is free software; you can redistribute it and/or modify it
       under the terms of the GNU General Public License as published by the
       Free Software Foundation; either version 3 of the License, or at your
       option any later version.

       This program is distributed in the hope that it will be useful, but
       WITHOUT ANY WARRANTY; without even the implied warranty of
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
       General Public License for more details.

       You should have received a copy of the GNU General Public License along
       with this program.  If not, see <http://www.gnu.org/licenses/>.

   Documentation license I
       Permission is granted to copy, distribute and/or modify this
       documentation under the terms of the GNU Free Documentation License,
       Version 1.3 or any later version published by the Free Software
       Foundation; with no Invariant Sections, with no Front-Cover Texts, and
       with no Back-Cover Texts.  A copy of the license is included in the
       file fdl.txt.

   Documentation license II
       You are free:

       to Share to copy, distribute and transmit the work

       to Remix to adapt the work

       Under the following conditions:

       Attribution
                You must attribute the work in the manner specified by the
                author or licensor (but not in any way that suggests that they
                endorse you or your use of the work).

       Share Alike
                If you alter, transform, or build upon this work, you may
                distribute the resulting work only under the same, similar or
                a compatible license.

       With the understanding that:

       Waiver   Any of the above conditions can be waived if you get
                permission from the copyright holder.

       Public Domain
                Where the work or any of its elements is in the public domain
                under applicable law, that status is in no way affected by the
                license.

       Other Rights
                In no way are any of the following rights affected by the
                license:

                o Your fair dealing or fair use rights, or other applicable
                  copyright exceptions and limitations;

                o The author's moral rights;

                o Rights other persons may have either in the work itself or
                  in how the work is used, such as publicity or privacy
                  rights.

       Notice   For any reuse or distribution, you must make clear to others
                the license terms of this work.

       A copy of the full license is included in the file as cc-by-sa.txt.

DEPENDENCIES
       GNU parallel uses Perl, and the Perl modules Getopt::Long, IPC::Open3,
       Symbol, IO::File, POSIX, and File::Temp. For remote usage it also uses
       rsync with ssh.


ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:


       +---------------+------------------+
       |ATTRIBUTE TYPE | ATTRIBUTE VALUE  |
       +---------------+------------------+
       |Availability   | shell/parallel   |
       +---------------+------------------+
       |Stability      | Uncommitted      |
       +---------------+------------------+
SEE ALSO
       ssh(1), rsync(1), find(1), xargs(1), dirname, make(1), pexec(1),
       ppss(1), xjobs(1), prll(1), dxargs(1), mdm(1),



NOTES
       This software was built from source available at
       https://java.net/projects/solaris-userland.  The original community
       source was downloaded from
       http://ftp.gnu.org/gnu/parallel/parallel-20121122.tar.bz2

       Further information about this software can be found on the open source
       community website at http://www.gnu.org/software/parallel/.



20121122                          2012-11-21                       PARALLEL(1)