zshmisc
(1)
Name
zshmisc - everything and then some
Synopsis
Please see following description for synopsis
Description
User Commands ZSHMISC(1)
NAME
zshmisc - everything and then some
SIMPLE COMMANDS & PIPELINES
A simple command is a sequence of optional parameter assign-
ments followed by blank-separated words, with optional redi-
rections interspersed. The first word is the command to be
executed, and the remaining words, if any, are arguments to
the command. If a command name is given, the parameter
assignments modify the environment of the command when it is
executed. The value of a simple command is its exit status,
or 128 plus the signal number if terminated by a signal.
For example,
echo foo
is a simple command with arguments.
A pipeline is either a simple command, or a sequence of two
or more simple commands where each command is separated from
the next by `|' or `|&'. Where commands are separated by
`|', the standard output of the first command is connected
to the standard input of the next. `|&' is shorthand for
`2>&1 |', which connects both the standard output and the
standard error of the command to the standard input of the
next. The value of a pipeline is the value of the last com-
mand, unless the pipeline is preceded by `!' in which case
the value is the logical inverse of the value of the last
command. For example,
echo foo | sed 's/foo/bar/'
is a pipeline, where the output (`foo' plus a newline) of
the first command will be passed to the input of the second.
If a pipeline is preceded by `coproc', it is executed as a
coprocess; a two-way pipe is established between it and the
parent shell. The shell can read from or write to the
coprocess by means of the `>&p' and `<&p' redirection opera-
tors or with `print -p' and `read -p'. A pipeline cannot be
preceded by both `coproc' and `!'. If job control is
active, the coprocess can be treated in other than input and
output as an ordinary background job.
A sublist is either a single pipeline, or a sequence of two
or more pipelines separated by `&&' or `||'. If two pipe-
lines are separated by `&&', the second pipeline is executed
only if the first succeeds (returns a zero status). If two
pipelines are separated by `||', the second is executed only
if the first fails (returns a nonzero status). Both opera-
tors have equal precedence and are left associative. The
value of the sublist is the value of the last pipeline
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executed. For example,
dmesg | grep panic && print yes
is a sublist consisting of two pipelines, the second just a
simple command which will be executed if and only if the
grep command returns a zero status. If it does not, the
value of the sublist is that return status, else it is the
status returned by the print (almost certainly zero).
A list is a sequence of zero or more sublists, in which each
sublist is terminated by `;', `&', `&|', `&!', or a newline.
This terminator may optionally be omitted from the last sub-
list in the list when the list appears as a complex command
inside `(...)' or `{...}'. When a sublist is terminated by
`;' or newline, the shell waits for it to finish before exe-
cuting the next sublist. If a sublist is terminated by a
`&', `&|', or `&!', the shell executes the last pipeline in
it in the background, and does not wait for it to finish
(note the difference from other shells which execute the
whole sublist in the background). A backgrounded pipeline
returns a status of zero.
More generally, a list can be seen as a set of any shell
commands whatsoever, including the complex commands below;
this is implied wherever the word `list' appears in later
descriptions. For example, the commands in a shell function
form a special sort of list.
PRECOMMAND MODIFIERS
A simple command may be preceded by a precommand modifier,
which will alter how the command is interpreted. These mod-
ifiers are shell builtin commands with the exception of
nocorrect which is a reserved word.
- The command is executed with a `-' prepended to its
argv[0] string.
builtin
The command word is taken to be the name of a builtin
command, rather than a shell function or external com-
mand.
command [ -pvV ]
The command word is taken to be the name of an external
command, rather than a shell function or builtin. If
the POSIX_BUILTINS option is set, builtins will also be
executed but certain special properties of them are
suppressed. The -p flag causes a default path to be
searched instead of that in $path. With the -v flag,
command is similar to whence and with -V, it is equiva-
lent to whence -v.
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exec [ -cl ] [ -a argv0 ]
The following command together with any arguments is
run in place of the current process, rather than as a
sub-process. The shell does not fork and is replaced.
The shell does not invoke TRAPEXIT, nor does it source
zlogout files. The options are provided for compati-
bility with other shells.
The -c option clears the environment.
The -l option is equivalent to the - precommand modi-
fier, to treat the replacement command as a login
shell; the command is executed with a - prepended to
its argv[0] string. This flag has no effect if used
together with the -a option.
The -a option is used to specify explicitly the argv[0]
string (the name of the command as seen by the process
itself) to be used by the replacement command and is
directly equivalent to setting a value for the ARGV0
environment variable.
nocorrect
Spelling correction is not done on any of the words.
This must appear before any other precommand modifier,
as it is interpreted immediately, before any parsing is
done. It has no effect in non-interactive shells.
noglob
Filename generation (globbing) is not performed on any
of the words.
COMPLEX COMMANDS
A complex command in zsh is one of the following:
if list then list [ elif list then list ] ... [ else list ]
fi
The if list is executed, and if it returns a zero exit
status, the then list is executed. Otherwise, the elif
list is executed and if its status is zero, the then
list is executed. If each elif list returns nonzero
status, the else list is executed.
for name ... [ in word ... ] term do list done
where term is at least one newline or ;. Expand the
list of words, and set the parameter name to each of
them in turn, executing list each time. If the in word
is omitted, use the positional parameters instead of
the words.
More than one parameter name can appear before the list
of words. If N names are given, then on each execution
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of the loop the next N words are assigned to the corre-
sponding parameters. If there are more names than
remaining words, the remaining parameters are each set
to the empty string. Execution of the loop ends when
there is no remaining word to assign to the first name.
It is only possible for in to appear as the first name
in the list, else it will be treated as marking the end
of the list.
for (( [expr1] ; [expr2] ; [expr3] )) do list done
The arithmetic expression expr1 is evaluated first (see
the section `Arithmetic Evaluation'). The arithmetic
expression expr2 is repeatedly evaluated until it eval-
uates to zero and when non-zero, list is executed and
the arithmetic expression expr3 evaluated. If any
expression is omitted, then it behaves as if it evalu-
ated to 1.
while list do list done
Execute the do list as long as the while list returns a
zero exit status.
until list do list done
Execute the do list as long as until list returns a
nonzero exit status.
repeat word do list done
word is expanded and treated as an arithmetic expres-
sion, which must evaluate to a number n. list is then
executed n times.
The repeat syntax is disabled by default when the shell
starts in a mode emulating another shell. It can be
enabled with the command `enable -r repeat'
... esac
case word in [ [(] pattern [ | pattern ] ... ) list
(;;|;&|;|) ]
Execute the list associated with the first pattern that
matches word, if any. The form of the patterns is the
same as that used for filename generation. See the
section `Filename Generation'.
If the list that is executed is terminated with ;&
rather than ;;, the following list is also executed.
The rule for the terminator of the following list ;;,
;& or ;| is applied unless the esac is reached.
If the list that is executed is terminated with ;| the
shell continues to scan the patterns looking for the
next match, executing the corresponding list, and
applying the rule for the corresponding terminator ;;,
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;& or ;|. Note that word is not re-expanded; all
applicable patterns are tested with the same word.
select name [ in word ... term ] do list done
where term is one or more newline or ; to terminate the
words. Print the set of words, each preceded by a num-
ber. If the in word is omitted, use the positional
parameters. The PROMPT3 prompt is printed and a line
is read from the line editor if the shell is interac-
tive and that is active, or else standard input. If
this line consists of the number of one of the listed
words, then the parameter name is set to the word cor-
responding to this number. If this line is empty, the
selection list is printed again. Otherwise, the value
of the parameter name is set to null. The contents of
the line read from standard input is saved in the
parameter REPLY. list is executed for each selection
until a break or end-of-file is encountered.
( list )
Execute list in a subshell. Traps set by the trap
builtin are reset to their default values while execut-
ing list.
{ list }
Execute list.
{ try-list } always { always-list }
First execute try-list. Regardless of errors, or
break, continue, or return commands encountered within
try-list, execute always-list. Execution then contin-
ues from the result of the execution of try-list; in
other words, any error, or break, continue, or return
command is treated in the normal way, as if always-list
were not present. The two chunks of code are referred
to as the `try block' and the `always block'.
Optional newlines or semicolons may appear after the
always; note, however, that they may not appear between
the preceding closing brace and the always.
An `error' in this context is a condition such as a
syntax error which causes the shell to abort execution
of the current function, script, or list. Syntax
errors encountered while the shell is parsing the code
do not cause the always-list to be executed. For exam-
ple, an erroneously constructed if block in try-list
would cause the shell to abort during parsing, so that
always-list would not be executed, while an erroneous
substitution such as ${*foo*} would cause a run-time
error, after which always-list would be executed.
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An error condition can be tested and reset with the
special integer variable TRY_BLOCK_ERROR. Outside an
always-list the value is irrelevant, but it is ini-
tialised to -1. Inside always-list, the value is 1 if
an error occurred in the try-list, else 0. If
TRY_BLOCK_ERROR is set to 0 during the always-list, the
error condition caused by the try-list is reset, and
shell execution continues normally after the end of
always-list. Altering the value during the try-list is
not useful (unless this forms part of an enclosing
always block).
Regardless of TRY_BLOCK_ERROR, after the end of
always-list the normal shell status $? is the value
returned from always-list. This will be non-zero if
there was an error, even if TRY_BLOCK_ERROR was set to
zero.
The following executes the given code, ignoring any
errors it causes. This is an alternative to the usual
convention of protecting code by executing it in a sub-
shell.
{
# code which may cause an error
} always {
# This code is executed regardless of the error.
(( TRY_BLOCK_ERROR = 0 ))
}
# The error condition has been reset.
An exit command (or a return command executed at the
outermost function level of a script) encountered in
try-list does not cause the execution of always-list.
Instead, the shell exits immediately after any EXIT
trap has been executed.
function word ... [ () ] [ term ] { list }
word ... () [ term ] { list }
word ... () [ term ] command
where term is one or more newline or ;. Define a func-
tion which is referenced by any one of word. Normally,
only one word is provided; multiple words are usually
only useful for setting traps. The body of the func-
tion is the list between the { and }. See the section
`Functions'.
If the option SH_GLOB is set for compatibility with
other shells, then whitespace may appear between
between the left and right parentheses when there is a
single word; otherwise, the parentheses will be
treated as forming a globbing pattern in that case.
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time [ pipeline ]
The pipeline is executed, and timing statistics are
reported on the standard error in the form specified by
the TIMEFMT parameter. If pipeline is omitted, print
statistics about the shell process and its children.
[[ exp ]]
Evaluates the conditional expression exp and return a
zero exit status if it is true. See the section `Con-
ditional Expressions' for a description of exp.
ALTERNATE FORMS FOR COMPLEX COMMANDS
Many of zsh's complex commands have alternate forms. These
are non-standard and are likely not to be obvious even to
seasoned shell programmers; they should not be used anywhere
that portability of shell code is a concern.
The short versions below only work if sublist is of the form
`{ list }' or if the SHORT_LOOPS option is set. For the if,
while and until commands, in both these cases the test part
of the loop must also be suitably delimited, such as by `[[
... ]]' or `(( ... ))', else the end of the test will not be
recognized. For the for, repeat, case and select commands
no such special form for the arguments is necessary, but the
other condition (the special form of sublist or use of the
SHORT_LOOPS option) still applies.
if list { list } [ elif list { list } ] ... [ else { list }
]
An alternate form of if. The rules mean that
if [[ -o ignorebraces ]] {
print yes
}
works, but
if true { # Does not work!
print yes
}
does not, since the test is not suitably delimited.
if list sublist
A short form of the alternate `if'. The same limita-
tions on the form of list apply as for the previous
form.
for name ... ( word ... ) sublist
A short form of for.
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for name ... [ in word ... ] term sublist
where term is at least one newline or ;. Another short
form of for.
for (( [expr1] ; [expr2] ; [expr3] )) sublist
A short form of the arithmetic for command.
foreach name ... ( word ... ) list end
Another form of for.
while list { list }
An alternative form of while. Note the limitations on
the form of list mentioned above.
until list { list }
An alternative form of until. Note the limitations on
the form of list mentioned above.
repeat word sublist
This is a short form of repeat.
... }
case word { [ [(] pattern [ | pattern ] ... ) list
(;;|;&|;|) ]
An alternative form of case.
select name [ in word term ] sublist
where term is at least one newline or ;. A short form
of select.
RESERVED WORDS
The following words are recognized as reserved words when
used as the first word of a command unless quoted or dis-
abled using disable -r:
do done esac then elif else fi for case if while function
repeat time until select coproc nocorrect foreach end ! [[ {
}
Additionally, `}' is recognized in any position if neither
the IGNORE_BRACES option nor the IGNORE_CLOSE_BRACES option
is set.
ERRORS
Certain errors are treated as fatal by the shell: in an
interactive shell, they cause control to return to the com-
mand line, and in a non-interactive shell they cause the
shell to be aborted. In older versions of zsh, a non-inter-
active shell running a script would not abort completely,
but would resume execution at the next command to be read
from the script, skipping the remainder of any functions or
shell constructs such as loops or conditions; this somewhat
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illogical behaviour can be recovered by setting the option
CONTINUE_ON_ERROR.
Fatal errors found in non-interactive shells include:
Failure to parse shell options passed when invoking the
shell
Failure to change options with the set builtin
Parse errors of all sorts, including failures to parse
mathematical expressions
Failures to set or modify variable behaviour with typeset,
local, declare, export, integer, float
Execution of incorrectly positioned loop control structures
(continue, break)
Attempts to use regular expression with no regular expres-
sion
module available
Disallowed operations when the RESTRICTED options is set
Failure to create a pipe needed for a pipeline
Failure to create a multio
Failure to autoload a module needed for a declared shell
feature
Errors creating command or process substitutions
Syntax errors in glob qualifiers
File generation errors where not caught by the option
BAD_PATTERN
All bad patterns used for matching within case statements
File generation failures where not caused by NO_MATCH or
All file generation errors where the pattern was used to
create a
multio
Memory errors where detected by the shell
Invalid subscripts to shell variables
Attempts to assign read-only variables
type
Logical errors with variables such as assignment to the
wrong
Use of invalid variable names
Errors in variable substitution syntax
Failure to convert characters in $'...' expressions
similar options
If the POSIX_BUILTINS option is set, more errors associated
with shell builtin commands are treated as fatal, as speci-
fied by the POSIX standard.
COMMENTS
In non-interactive shells, or in interactive shells with the
INTERACTIVE_COMMENTS option set, a word beginning with the
third character of the histchars parameter (`#' by default)
causes that word and all the following characters up to a
newline to be ignored.
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ALIASING
Every token in the shell input is checked to see if there is
an alias defined for it. If so, it is replaced by the text
of the alias if it is in command position (if it could be
the first word of a simple command), or if the alias is
global. If the text ends with a space, the next word in the
shell input is treated as though it were in command position
for purposes of alias expansion. An alias is defined using
the alias builtin; global aliases may be defined using the
-g option to that builtin.
Alias expansion is done on the shell input before any other
expansion except history expansion. Therefore, if an alias
is defined for the word foo, alias expansion may be avoided
by quoting part of the word, e.g. \foo. Any form of quoting
works, although there is nothing to prevent an alias being
defined for the quoted form such as \foo as well. For use
with completion, which would remove an initial backslash
followed by a character that isn't special, it may be more
convenient to quote the word by starting with a single
quote, i.e. 'foo; completion will automatically add the
trailing single quote.
There is a commonly encountered problem with aliases illus-
trated by the following code:
alias echobar='echo bar'; echobar
This prints a message that the command echobar could not be
found. This happens because aliases are expanded when the
code is read in; the entire line is read in one go, so that
when echobar is executed it is too late to expand the newly
defined alias. This is often a problem in shell scripts,
functions, and code executed with `source' or `.'. Conse-
quently, use of functions rather than aliases is recommended
in non-interactive code.
Note also the unhelpful interaction of aliases and function
definitions:
alias func='noglob func'
func() {
echo Do something with $*
}
Because aliases are expanded in function definitions, this
causes the following command to be executed:
noglob func() {
echo Do something with $*
}
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which defines noglob as well as func as functions with the
body given. To avoid this, either quote the name func or
use the alternative function definition form `function
func'. Ensuring the alias is defined after the function
works but is problematic if the code fragment might be
re-executed.
QUOTING
A character may be quoted (that is, made to stand for
itself) by preceding it with a `\'. `\' followed by a new-
line is ignored.
A string enclosed between `$'' and `'' is processed the same
way as the string arguments of the print builtin, and the
resulting string is considered to be entirely quoted. A
literal `'' character can be included in the string by using
the `\'' escape.
All characters enclosed between a pair of single quotes ('')
that is not preceded by a `$' are quoted. A single quote
cannot appear within single quotes unless the option
RC_QUOTES is set, in which case a pair of single quotes are
turned into a single quote. For example,
print ''''
outputs nothing apart from a newline if RC_QUOTES is not
set, but one single quote if it is set.
Inside double quotes (""), parameter and command substitu-
tion occur, and `\' quotes the characters `\', ``', `"', and
`$'.
REDIRECTION
If a command is followed by & and job control is not active,
then the default standard input for the command is the empty
file /dev/null. Otherwise, the environment for the execu-
tion of a command contains the file descriptors of the
invoking shell as modified by input/output specifications.
The following may appear anywhere in a simple command or may
precede or follow a complex command. Expansion occurs
before word or digit is used except as noted below. If the
result of substitution on word produces more than one file-
name, redirection occurs for each separate filename in turn.
< word
Open file word for reading as standard input.
<> word
Open file word for reading and writing as standard
input. If the file does not exist then it is created.
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> word
Open file word for writing as standard output. If the
file does not exist then it is created. If the file
exists, and the CLOBBER option is unset, this causes an
error; otherwise, it is truncated to zero length.
>| word
>! word
Same as >, except that the file is truncated to zero
length if it exists, even if CLOBBER is unset.
>> word
Open file word for writing in append mode as standard
output. If the file does not exist, and the CLOBBER
option is unset, this causes an error; otherwise, the
file is created.
>>| word
>>! word
Same as >>, except that the file is created if it does
not exist, even if CLOBBER is unset.
<<[-] word
The shell input is read up to a line that is the same
as word, or to an end-of-file. No parameter expansion,
command substitution or filename generation is per-
formed on word. The resulting document, called a
here-document, becomes the standard input.
If any character of word is quoted with single or dou-
ble quotes or a `\', no interpretation is placed upon
the characters of the document. Otherwise, parameter
and command substitution occurs, `\' followed by a new-
line is removed, and `\' must be used to quote the
characters `\', `$', ``' and the first character of
word.
Note that word itself does not undergo shell expansion.
Backquotes in word do not have their usual effect;
instead they behave similarly to double quotes, except
that the backquotes themselves are passed through
unchanged. (This information is given for completeness
and it is not recommended that backquotes be used.)
Quotes in the form $'...' have their standard effect of
expanding backslashed references to special characters.
If <<- is used, then all leading tabs are stripped from
word and from the document.
<<< word
Perform shell expansion on word and pass the result to
standard input. This is known as a here-string.
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Compare the use of word in here-documents above, where
word does not undergo shell expansion.
<& number
>& number
The standard input/output is duplicated from file
descriptor number (see dup2(2)).
<& -
>& - Close the standard input/output.
<& p
>& p The input/output from/to the coprocess is moved to the
standard input/output.
>& word
&> word
(Except where `>& word' matches one of the above syn-
taxes; `&>' can always be used to avoid this ambigu-
ity.) Redirects both standard output and standard
error (file descriptor 2) in the manner of `> word'.
Note that this does not have the same effect as `> word
2>&1' in the presence of multios (see the section
below).
>&| word
>&! word
&>| word
&>! word
Redirects both standard output and standard error (file
descriptor 2) in the manner of `>| word'.
>>& word
&>> word
Redirects both standard output and standard error (file
descriptor 2) in the manner of `>> word'.
>>&| word
>>&! word
&>>| word
&>>! word
Redirects both standard output and standard error (file
descriptor 2) in the manner of `>>| word'.
If one of the above is preceded by a digit, then the file
descriptor referred to is that specified by the digit
instead of the default 0 or 1. The order in which redirec-
tions are specified is significant. The shell evaluates
each redirection in terms of the (file descriptor, file)
association at the time of evaluation. For example:
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... 1>fname 2>&1
first associates file descriptor 1 with file fname. It then
associates file descriptor 2 with the file associated with
file descriptor 1 (that is, fname). If the order of redi-
rections were reversed, file descriptor 2 would be associ-
ated with the terminal (assuming file descriptor 1 had been)
and then file descriptor 1 would be associated with file
fname.
The `|&' command separator described in Simple Commands &
Pipelines in zshmisc(1) is a shorthand for `2>&1 |'.
The various forms of process substitution, `<(list)', and
`=(list())' for input and `>(list)' for output, are often
used together with redirection. For example, if word in an
output redirection is of the form `>(list)' then the output
is piped to the command represented by list. See Process
Substitution in zshexpn(1).
OPENING FILE DESCRIPTORS USING PARAMETERS
When the shell is parsing arguments to a command, and the
shell option IGNORE_BRACES is not set, a different form of
redirection is allowed: instead of a digit before the opera-
tor there is a valid shell identifier enclosed in braces.
The shell will open a new file descriptor that is guaranteed
to be at least 10 and set the parameter named by the identi-
fier to the file descriptor opened. No whitespace is
allowed between the closing brace and the redirection char-
acter. For example:
... {myfd}>&1
This opens a new file descriptor that is a duplicate of file
descriptor 1 and sets the parameter myfd to the number of
the file descriptor, which will be at least 10. The new
file descriptor can be written to using the syntax >&$myfd.
The syntax {varid}>&-, for example {myfd}>&-, may be used to
close a file descriptor opened in this fashion. Note that
the parameter given by varid must previously be set to a
file descriptor in this case.
It is an error to open or close a file descriptor in this
fashion when the parameter is readonly. However, it is not
an error to read or write a file descriptor using <&$param
or >&$param if param is readonly.
If the option CLOBBER is unset, it is an error to open a
file descriptor using a parameter that is already set to an
open file descriptor previously allocated by this mechanism.
Unsetting the parameter before using it for allocating a
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file descriptor avoids the error.
Note that this mechanism merely allocates or closes a file
descriptor; it does not perform any redirections from or to
it. It is usually convenient to allocate a file descriptor
prior to use as an argument to exec. The syntax does not in
any case work when used around complex commands such as
parenthesised subshells or loops, where the opening brace is
interpreted as part of a command list to be executed in the
current shell.
The following shows a typical sequence of allocation, use,
and closing of a file descriptor:
integer myfd
exec {myfd}>~/logs/mylogfile.txt
print This is a log message. >&$myfd
exec {myfd}>&-
Note that the expansion of the variable in the expression
>&$myfd occurs at the point the redirection is opened. This
is after the expansion of command arguments and after any
redirections to the left on the command line have been pro-
cessed.
MULTIOS
If the user tries to open a file descriptor for writing more
than once, the shell opens the file descriptor as a pipe to
a process that copies its input to all the specified out-
puts, similar to tee, provided the MULTIOS option is set, as
it is by default. Thus:
date >foo >bar
writes the date to two files, named `foo' and `bar'. Note
that a pipe is an implicit redirection; thus
date >foo | cat
writes the date to the file `foo', and also pipes it to cat.
If the MULTIOS option is set, the word after a redirection
operator is also subjected to filename generation (glob-
bing). Thus
: > *
will truncate all files in the current directory, assuming
there's at least one. (Without the MULTIOS option, it would
create an empty file called `*'.) Similarly, you can do
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echo exit 0 >> *.sh
If the user tries to open a file descriptor for reading more
than once, the shell opens the file descriptor as a pipe to
a process that copies all the specified inputs to its output
in the order specified, similar to cat, provided the MULTIOS
option is set. Thus
sort <foo <fubar
or even
sort <f{oo,ubar}
is equivalent to `cat foo fubar | sort'.
Expansion of the redirection argument occurs at the point
the redirection is opened, at the point described above for
the expansion of the variable in >&$myfd.
Note that a pipe is an implicit redirection; thus
cat bar | sort <foo
is equivalent to `cat bar foo | sort' (note the order of the
inputs).
If the MULTIOS option is unset, each redirection replaces
the previous redirection for that file descriptor. However,
all files redirected to are actually opened, so
echo foo > bar > baz
when MULTIOS is unset will truncate bar, and write `foo'
into baz.
There is a problem when an output multio is attached to an
external program. A simple example shows this:
cat file >file1 >file2
cat file1 file2
Here, it is possible that the second `cat' will not display
the full contents of file1 and file2 (i.e. the original con-
tents of file repeated twice).
The reason for this is that the multios are spawned after
the cat process is forked from the parent shell, so the par-
ent shell does not wait for the multios to finish writing
data. This means the command as shown can exit before file1
and file2 are completely written. As a workaround, it is
possible to run the cat process as part of a job in the
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current shell:
{ cat file } >file >file2
Here, the {...} job will pause to wait for both files to be
written.
REDIRECTIONS WITH NO COMMAND
When a simple command consists of one or more redirection
operators and zero or more parameter assignments, but no
command name, zsh can behave in several ways.
If the parameter NULLCMD is not set or the option CSH_NULL-
CMD is set, an error is caused. This is the csh behavior
and CSH_NULLCMD is set by default when emulating csh.
If the option SH_NULLCMD is set, the builtin `:' is inserted
as a command with the given redirections. This is the
default when emulating sh or ksh.
Otherwise, if the parameter NULLCMD is set, its value will
be used as a command with the given redirections. If both
NULLCMD and READNULLCMD are set, then the value of the lat-
ter will be used instead of that of the former when the re-
direction is an input. The default for NULLCMD is `cat' and
for READNULLCMD is `more'. Thus
< file
shows the contents of file on standard output, with paging
if that is a terminal. NULLCMD and READNULLCMD may refer to
shell functions.
COMMAND EXECUTION
If a command name contains no slashes, the shell attempts to
locate it. If there exists a shell function by that name,
the function is invoked as described in the section `Func-
tions'. If there exists a shell builtin by that name, the
builtin is invoked.
Otherwise, the shell searches each element of $path for a
directory containing an executable file by that name. If
the search is unsuccessful, the shell prints an error mes-
sage and returns a nonzero exit status.
If execution fails because the file is not in executable
format, and the file is not a directory, it is assumed to be
a shell script. /bin/sh is spawned to execute it. If the
program is a file beginning with `#!', the remainder of the
first line specifies an interpreter for the program. The
shell will execute the specified interpreter on operating
systems that do not handle this executable format in the
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kernel.
If no external command is found but a function com-
mand_not_found_handler exists the shell executes this func-
tion with all command line arguments. The function should
return status zero if it successfully handled the command,
or non-zero status if it failed. In the latter case the
standard handling is applied: `command not found' is printed
to standard error and the shell exits with status 127. Note
that the handler is executed in a subshell forked to execute
an external command, hence changes to directories, shell
parameters, etc. have no effect on the main shell.
FUNCTIONS
Shell functions are defined with the function reserved word
or the special syntax `funcname ()'. Shell functions are
read in and stored internally. Alias names are resolved
when the function is read. Functions are executed like com-
mands with the arguments passed as positional parameters.
(See the section `Command Execution'.)
Functions execute in the same process as the caller and
share all files and present working directory with the
caller. A trap on EXIT set inside a function is executed
after the function completes in the environment of the
caller.
The return builtin is used to return from function calls.
Function identifiers can be listed with the functions
builtin. Functions can be undefined with the unfunction
builtin.
AUTOLOADING FUNCTIONS
A function can be marked as undefined using the autoload
builtin (or `functions -u' or `typeset -fu'). Such a func-
tion has no body. When the function is first executed, the
shell searches for its definition using the elements of the
fpath variable. Thus to define functions for autoloading, a
typical sequence is:
fpath=(~/myfuncs $fpath)
autoload myfunc1 myfunc2 ...
The usual alias expansion during reading will be suppressed
if the autoload builtin or its equivalent is given the
option -U. This is recommended for the use of functions sup-
plied with the zsh distribution. Note that for functions
precompiled with the zcompile builtin command the flag -U
must be provided when the .zwc file is created, as the cor-
responding information is compiled into the latter.
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For each element in fpath, the shell looks for three possi-
ble files, the newest of which is used to load the defini-
tion for the function:
element.zwc
A file created with the zcompile builtin command, which
is expected to contain the definitions for all func-
tions in the directory named element. The file is
treated in the same manner as a directory containing
files for functions and is searched for the definition
of the function. If the definition is not found, the
search for a definition proceeds with the other two
possibilities described below.
If element already includes a .zwc extension (i.e. the
extension was explicitly given by the user), element is
searched for the definition of the function without
comparing its age to that of other files; in fact,
there does not need to be any directory named element
without the suffix. Thus including an element such as
`/usr/local/funcs.zwc' in fpath will speed up the
search for functions, with the disadvantage that func-
tions included must be explicitly recompiled by hand
before the shell notices any changes.
element/function.zwc
A file created with zcompile, which is expected to con-
tain the definition for function. It may include other
function definitions as well, but those are neither
loaded nor executed; a file found in this way is
searched only for the definition of function.
element/function
A file of zsh command text, taken to be the definition
for function.
In summary, the order of searching is, first, in the parents
of directories in fpath for the newer of either a compiled
directory or a directory in fpath; second, if more than one
of these contains a definition for the function that is
sought, the leftmost in the fpath is chosen; and third,
within a directory, the newer of either a compiled function
or an ordinary function definition is used.
If the KSH_AUTOLOAD option is set, or the file contains only
a simple definition of the function, the file's contents
will be executed. This will normally define the function in
question, but may also perform initialization, which is exe-
cuted in the context of the function execution, and may
therefore define local parameters. It is an error if the
function is not defined by loading the file.
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Otherwise, the function body (with no surrounding `func-
name() {...}') is taken to be the complete contents of the
file. This form allows the file to be used directly as an
executable shell script. If processing of the file results
in the function being re-defined, the function itself is not
re-executed. To force the shell to perform initialization
and then call the function defined, the file should contain
initialization code (which will be executed then discarded)
in addition to a complete function definition (which will be
retained for subsequent calls to the function), and a call
to the shell function, including any arguments, at the end.
For example, suppose the autoload file func contains
func() { print This is func; }
print func is initialized
then `func; func' with KSH_AUTOLOAD set will produce both
messages on the first call, but only the message `This is
func' on the second and subsequent calls. Without
KSH_AUTOLOAD set, it will produce the initialization message
on the first call, and the other message on the second and
subsequent calls.
It is also possible to create a function that is not marked
as autoloaded, but which loads its own definition by search-
ing fpath, by using `autoload -X' within a shell function.
For example, the following are equivalent:
myfunc() {
autoload -X
}
myfunc args...
and
unfunction myfunc # if myfunc was defined
autoload myfunc
myfunc args...
In fact, the functions command outputs `builtin autoload -X'
as the body of an autoloaded function. This is done so that
eval "$(functions)"
produces a reasonable result. A true autoloaded function
can be identified by the presence of the comment `# unde-
fined' in the body, because all comments are discarded from
defined functions.
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To load the definition of an autoloaded function myfunc
without executing myfunc, use:
autoload +X myfunc
ANONYMOUS FUNCTIONS
If no name is given for a function, it is `anonymous' and is
handled specially. Either form of function definition may
be used: a `()' with no preceding name, or a `function' with
an immediately following open brace. The function is exe-
cuted immediately at the point of definition and is not
stored for future use. The function name is set to
`(anon)'.
Arguments to the function may be specified as words follow-
ing the closing brace defining the function, hence if there
are none no arguments (other than $0) are set. This is a
difference from the way other functions are parsed: normal
function definitions may be followed by certain keywords
such as `else' or `fi', which will be treated as arguments
to anonymous functions, so that a newline or semicolon is
needed to force keyword interpretation.
Note also that the argument list of any enclosing script or
function is hidden (as would be the case for any other func-
tion called at this point).
Redirections may be applied to the anonymous function in the
same manner as to a current-shell structure enclosed in
braces. The main use of anonymous functions is to provide a
scope for local variables. This is particularly convenient
in start-up files as these do not provide their own local
variable scope.
For example,
variable=outside
function {
local variable=inside
print "I am $variable with arguments $*"
} this and that
print "I am $variable"
outputs the following:
I am inside with arguments this and that
I am outside
Note that function definitions with arguments that expand to
nothing, for example `name=; function $name { ... }', are
not treated as anonymous functions. Instead, they are
treated as normal function definitions where the definition
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is silently discarded.
SPECIAL FUNCTIONS
Certain functions, if defined, have special meaning to the
shell.
Hook Functions
For the functions below, it is possible to define an array
that has the same name as the function with `_functions'
appended. Any element in such an array is taken as the name
of a function to execute; it is executed in the same context
and with the same arguments as the basic function. For
example, if $chpwd_functions is an array containing the val-
ues `mychpwd', `chpwd_save_dirstack', then the shell
attempts to execute the functions `chpwd', `mychpwd' and
`chpwd_save_dirstack', in that order. Any function that
does not exist is silently ignored. A function found by
this mechanism is referred to elsewhere as a `hook func-
tion'. An error in any function causes subsequent functions
not to be run. Note further that an error in a precmd hook
causes an immediately following periodic function not to run
(though it may run at the next opportunity).
chpwd
Executed whenever the current working directory is
changed.
periodic
If the parameter PERIOD is set, this function is exe-
cuted every $PERIOD seconds, just before a prompt.
Note that if multiple functions are defined using the
array periodic_functions only one period is applied to
the complete set of functions, and the scheduled time
is not reset if the list of functions is altered.
Hence the set of functions is always called together.
precmd
Executed before each prompt. Note that precommand
functions are not re-executed simply because the com-
mand line is redrawn, as happens, for example, when a
notification about an exiting job is displayed.
preexec
Executed just after a command has been read and is
about to be executed. If the history mechanism is
active (and the line was not discarded from the history
buffer), the string that the user typed is passed as
the first argument, otherwise it is an empty string.
The actual command that will be executed (including
expanded aliases) is passed in two different forms: the
second argument is a single-line, size-limited version
of the command (with things like function bodies
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elided); the third argument contains the full text that
is being executed.
zshaddhistory
Executed when a history line has been read interac-
tively, but before it is executed. The sole argument
is the complete history line (so that any terminating
newline will still be present).
If any of the hook functions returns status 1 (or any
non-zero value other than 2, though this is not guaran-
teed for future versions of the shell) the history line
will not be saved, although it lingers in the history
until the next line is executed, allowing you to reuse
or edit it immediately.
If any of the hook functions returns status 2 the his-
tory line will be saved on the internal history list,
but not written to the history file. In case of a con-
flict, the first non-zero status value is taken.
A hook function may call `fc -p ...' to switch the his-
tory context so that the history is saved in a differ-
ent file from the that in the global HISTFILE parame-
ter. This is handled specially: the history context is
automatically restored after the processing of the his-
tory line is finished.
The following example function works with one of the
options INC_APPEND_HISTORY or SHARE_HISTORY set, in
order that the line is written out immediately after
the history entry is added. It first adds the history
line to the normal history with the newline stripped,
which is usually the correct behaviour. Then it
switches the history context so that the line will be
written to a history file in the current directory.
zshaddhistory() {
print -sr -- ${1%%$'\n'}
fc -p .zsh_local_history
}
zshexit
Executed at the point where the main shell is about to
exit normally. This is not called by exiting sub-
shells, nor when the exec precommand modifier is used
before an external command. Also, unlike TRAPEXIT, it
is not called when functions exit.
Trap Functions
The functions below are treated specially but do not have
corresponding hook arrays.
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TRAPNAL
If defined and non-null, this function will be executed
whenever the shell catches a signal SIGNAL, where NAL
is a signal name as specified for the kill builtin.
The signal number will be passed as the first parameter
to the function.
If a function of this form is defined and null, the
shell and processes spawned by it will ignore SIGNAL.
The return status from the function is handled spe-
cially. If it is zero, the signal is assumed to have
been handled, and execution continues normally. Other-
wise, the shell will behave as interrupted except that
the return status of the trap is retained.
Programs terminated by uncaught signals typically
return the status 128 plus the signal number. Hence
the following causes the handler for SIGINT to print a
message, then mimic the usual effect of the signal.
TRAPINT() {
print "Caught SIGINT, aborting."
return $(( 128 + $1 ))
}
The functions TRAPZERR, TRAPDEBUG and TRAPEXIT are
never executed inside other traps.
TRAPDEBUG
If the option DEBUG_BEFORE_CMD is set (as it is by
default), executed before each command; otherwise exe-
cuted after each command. See the description of the
trap builtin in zshbuiltins(1) for details of addi-
tional features provided in debug traps.
TRAPEXIT
Executed when the shell exits, or when the current
function exits if defined inside a function. The value
of $? at the start of execution is the exit status of
the shell or the return status of the function exiting.
TRAPZERR
Executed whenever a command has a non-zero exit status.
However, the function is not executed if the command
occurred in a sublist followed by `&&' or `||'; only
the final command in a sublist of this type causes the
trap to be executed. The function TRAPERR acts the
same as TRAPZERR on systems where there is no SIGERR
(this is the usual case).
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The functions beginning `TRAP' may alternatively be defined
with the trap builtin: this may be preferable for some
uses. Setting a trap with one form removes any trap of the
other form for the same signal; removing a trap in either
form removes all traps for the same signal. The forms
TRAPNAL() {
# code
}
('function traps') and
trap '
# code
' NAL
('list traps') are equivalent in most ways, the exceptions
being the following:
o Function traps have all the properties of normal func-
tions, appearing in the list of functions and being
called with their own function context rather than the
context where the trap was triggered.
o The return status from function traps is special,
whereas a return from a list trap causes the surround-
ing context to return with the given status.
o Function traps are not reset within subshells, in
accordance with zsh behaviour; list traps are reset, in
accordance with POSIX behaviour.
JOBS
If the MONITOR option is set, an interactive shell asso-
ciates a job with each pipeline. It keeps a table of cur-
rent jobs, printed by the jobs command, and assigns them
small integer numbers. When a job is started asynchronously
with `&', the shell prints a line to standard error which
looks like:
[1] 1234
indicating that the job which was started asynchronously was
job number 1 and had one (top-level) process, whose process
ID was 1234.
If a job is started with `&|' or `&!', then that job is
immediately disowned. After startup, it does not have a
place in the job table, and is not subject to the job con-
trol features described here.
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If you are running a job and wish to do something else you
may hit the key ^Z (control-Z) which sends a TSTP signal to
the current job: this key may be redefined by the susp
option of the external stty command. The shell will then
normally indicate that the job has been `suspended', and
print another prompt. You can then manipulate the state of
this job, putting it in the background with the bg command,
or run some other commands and then eventually bring the job
back into the foreground with the foreground command fg. A
^Z takes effect immediately and is like an interrupt in that
pending output and unread input are discarded when it is
typed.
A job being run in the background will suspend if it tries
to read from the terminal.
Note that if the job running in the foreground is a shell
function, then suspending it will have the effect of causing
the shell to fork. This is necessary to separate the func-
tion's state from that of the parent shell performing the
job control, so that the latter can return to the command
line prompt. As a result, even if fg is used to continue
the job the function will no longer be part of the parent
shell, and any variables set by the function will not be
visible in the parent shell. Thus the behaviour is differ-
ent from the case where the function was never suspended.
Zsh is different from many other shells in this regard.
The same behaviour is found when the shell is executing code
as the right hand side of a pipeline or any complex shell
construct such as if, for, etc., in order that the entire
block of code can be managed as a single job. Background
jobs are normally allowed to produce output, but this can be
disabled by giving the command `stty tostop'. If you set
this tty option, then background jobs will suspend when they
try to produce output like they do when they try to read
input.
When a command is suspended and continued later with the fg
or wait builtins, zsh restores tty modes that were in effect
when it was suspended. This (intentionally) does not apply
if the command is continued via `kill -CONT', nor when it is
continued with bg.
There are several ways to refer to jobs in the shell. A job
can be referred to by the process ID of any process of the
job or by one of the following:
%number
The job with the given number.
%string
Any job whose command line begins with string.
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%?string
Any job whose command line contains string.
%% Current job.
%+ Equivalent to `%%'.
%- Previous job.
The shell learns immediately whenever a process changes
state. It normally informs you whenever a job becomes
blocked so that no further progress is possible. If the
NOTIFY option is not set, it waits until just before it
prints a prompt before it informs you. All such notifica-
tions are sent directly to the terminal, not to the standard
output or standard error.
When the monitor mode is on, each background job that com-
pletes triggers any trap set for CHLD.
When you try to leave the shell while jobs are running or
suspended, you will be warned that `You have suspended (run-
ning) jobs'. You may use the jobs command to see what they
are. If you do this or immediately try to exit again, the
shell will not warn you a second time; the suspended jobs
will be terminated, and the running jobs will be sent a
SIGHUP signal, if the HUP option is set.
To avoid having the shell terminate the running jobs, either
use the nohup command (see nohup(1)) or the disown builtin.
SIGNALS
The INT and QUIT signals for an invoked command are ignored
if the command is followed by `&' and the MONITOR option is
not active. The shell itself always ignores the QUIT sig-
nal. Otherwise, signals have the values inherited by the
shell from its parent (but see the TRAPNAL special functions
in the section `Functions').
Certain jobs are run asynchronously by the shell other than
those explicitly put into the background; even in cases
where the shell would usually wait for such jobs, an
explicit exit command or exit due to the option ERR_EXIT
will cause the shell to exit without waiting. Examples of
such asynchronous jobs are process substitution, see the
section PROCESS SUBSTITUTION in the zshexpn(1) manual page,
and the handler processes for multios, see the section MUL-
TIOS in the zshmisc(1) manual page.
ARITHMETIC EVALUATION
The shell can perform integer and floating point arithmetic,
either using the builtin let, or via a substitution of the
form $((...)). For integers, the shell is usually compiled
to use 8-byte precision where this is available, otherwise
precision is 4 bytes. This can be tested, for example, by
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giving the command `print - $(( 12345678901 ))'; if the num-
ber appears unchanged, the precision is at least 8 bytes.
Floating point arithmetic always uses the `double' type with
whatever corresponding precision is provided by the compiler
and the library.
The let builtin command takes arithmetic expressions as
arguments; each is evaluated separately. Since many of the
arithmetic operators, as well as spaces, require quoting, an
alternative form is provided: for any command which begins
with a `((', all the characters until a matching `))' are
treated as a quoted expression and arithmetic expansion per-
formed as for an argument of let. More precisely, `((...))'
is equivalent to `let "..."'. The return status is 0 if the
arithmetic value of the expression is non-zero, 1 if it is
zero, and 2 if an error occurred.
For example, the following statement
(( val = 2 + 1 ))
is equivalent to
let "val = 2 + 1"
both assigning the value 3 to the shell variable val and
returning a zero status.
Integers can be in bases other than 10. A leading `0x' or
`0X' denotes hexadecimal. Integers may also be of the form
`base#n', where base is a decimal number between two and
thirty-six representing the arithmetic base and n is a num-
ber in that base (for example, `16#ff' is 255 in hexadeci-
mal). The base# may also be omitted, in which case base 10
is used. For backwards compatibility the form `[base]n' is
also accepted.
An integer expression or a base given in the form `base#n'
may contain underscores (`_') after the leading digit for
visual guidance; these are ignored in computation. Examples
are 1_000_000 or 0xffff_ffff which are equivalent to 1000000
and 0xffffffff respectively.
It is also possible to specify a base to be used for output
in the form `[#base]', for example `[#16]'. This is used
when outputting arithmetical substitutions or when assigning
to scalar parameters, but an explicitly defined integer or
floating point parameter will not be affected. If an inte-
ger variable is implicitly defined by an arithmetic expres-
sion, any base specified in this way will be set as the
variable's output arithmetic base as if the option `-i base'
to the typeset builtin had been used. The expression has no
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precedence and if it occurs more than once in a mathematical
expression, the last encountered is used. For clarity it is
recommended that it appear at the beginning of an expres-
sion. As an example:
typeset -i 16 y
print $(( [#8] x = 32, y = 32 ))
print $x $y
outputs first `8#40', the rightmost value in the given out-
put base, and then `8#40 16#20', because y has been explic-
itly declared to have output base 16, while x (assuming it
does not already exist) is implicitly typed by the arith-
metic evaluation, where it acquires the output base 8.
If the C_BASES option is set, hexadecimal numbers in the
standard C format, for example 0xFF instead of the usual
`16#FF'. If the option OCTAL_ZEROES is also set (it is not
by default), octal numbers will be treated similarly and
hence appear as `077' instead of `8#77'. This option has no
effect on the output of bases other than hexadecimal and
octal, and these formats are always understood on input.
When an output base is specified using the `[#base]' syntax,
an appropriate base prefix will be output if necessary, so
that the value output is valid syntax for input. If the #
is doubled, for example `[##16]', then no base prefix is
output.
Floating point constants are recognized by the presence of a
decimal point or an exponent. The decimal point may be the
first character of the constant, but the exponent character
e or E may not, as it will be taken for a parameter name.
All numeric parts (before and after the decimal point and in
the exponent) may contain underscores after the leading
digit for visual guidance; these are ignored in computation.
An arithmetic expression uses nearly the same syntax and
associativity of expressions as in C.
In the native mode of operation, the following operators are
supported (listed in decreasing order of precedence):
+ - ! ~ ++ --
unary plus/minus, logical NOT, complement,
{pre,post}{in,de}crement
<< >>
bitwise shift left, right
& bitwise AND
^ bitwise XOR
| bitwise OR
** exponentiation
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* / %
multiplication, division, modulus (remainder)
+ - addition, subtraction
< > <= >=
comparison
== !=
equality and inequality
&& logical AND
|| ^^
logical OR, XOR
? : ternary operator
= += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
assignment
, comma operator
The operators `&&', `||', `&&=', and `||=' are short-cir-
cuiting, and only one of the latter two expressions in a
ternary operator is evaluated. Note the precedence of the
bitwise AND, OR, and XOR operators.
With the option C_PRECEDENCES the precedences (but no other
properties) of the operators are altered to be the same as
those in most other languages that support the relevant
operators:
+ - ! ~ ++ --
unary plus/minus, logical NOT, complement,
{pre,post}{in,de}crement
** exponentiation
* / %
multiplication, division, modulus (remainder)
+ - addition, subtraction
<< >>
bitwise shift left, right
< > <= >=
comparison
== !=
equality and inequality
& bitwise AND
^ bitwise XOR
| bitwise OR
&& logical AND
^^ logical XOR
|| logical OR
? : ternary operator
= += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
assignment
, comma operator
Note the precedence of exponentiation in both cases is below
that of unary operators, hence `-3**2' evaluates as `9', not
-9. Use parentheses where necessary: `-(3**2)'. This is
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User Commands ZSHMISC(1)
for compatibility with other shells.
Mathematical functions can be called with the syntax
`func(args)', where the function decides if the args is used
as a string or a comma-separated list of arithmetic expres-
sions. The shell currently defines no mathematical functions
by default, but the module zsh/mathfunc may be loaded with
the zmodload builtin to provide standard floating point
mathematical functions.
An expression of the form `##x' where x is any character
sequence such as `a', `^A', or `\M-\C-x' gives the value of
this character and an expression of the form `#foo' gives
the value of the first character of the contents of the
parameter foo. Character values are according to the char-
acter set used in the current locale; for multibyte charac-
ter handling the option MULTIBYTE must be set. Note that
this form is different from `$#foo', a standard parameter
substitution which gives the length of the parameter foo.
`#\' is accepted instead of `##', but its use is deprecated.
Named parameters and subscripted arrays can be referenced by
name within an arithmetic expression without using the
parameter expansion syntax. For example,
((val2 = val1 * 2))
assigns twice the value of $val1 to the parameter named
val2.
An internal integer representation of a named parameter can
be specified with the integer builtin. Arithmetic evalua-
tion is performed on the value of each assignment to a named
parameter declared integer in this manner. Assigning a
floating point number to an integer results in rounding down
to the next integer.
Likewise, floating point numbers can be declared with the
float builtin; there are two types, differing only in their
output format, as described for the typeset builtin. The
output format can be bypassed by using arithmetic substitu-
tion instead of the parameter substitution, i.e. `${float}'
uses the defined format, but `$((float))' uses a generic
floating point format.
Promotion of integer to floating point values is performed
where necessary. In addition, if any operator which
requires an integer (`~', `&', `|', `^', `%', `<<', `>>' and
their equivalents with assignment) is given a floating point
argument, it will be silently rounded down to the next inte-
ger.
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Scalar variables can hold integer or floating point values
at different times; there is no memory of the numeric type
in this case.
If a variable is first assigned in a numeric context without
previously being declared, it will be implicitly typed as
integer or float and retain that type either until the type
is explicitly changed or until the end of the scope. This
can have unforeseen consequences. For example, in the loop
for (( f = 0; f < 1; f += 0.1 )); do
# use $f
done
if f has not already been declared, the first assignment
will cause it to be created as an integer, and consequently
the operation `f += 0.1' will always cause the result to be
truncated to zero, so that the loop will fail. A simple fix
would be to turn the initialization into `f = 0.0'. It is
therefore best to declare numeric variables with explicit
types.
CONDITIONAL EXPRESSIONS
A conditional expression is used with the [[ compound com-
mand to test attributes of files and to compare strings.
Each expression can be constructed from one or more of the
following unary or binary expressions:
-a file
true if file exists.
-b file
true if file exists and is a block special file.
-c file
true if file exists and is a character special file.
-d file
true if file exists and is a directory.
-e file
true if file exists.
-f file
true if file exists and is a regular file.
-g file
true if file exists and has its setgid bit set.
-h file
true if file exists and is a symbolic link.
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-k file
true if file exists and has its sticky bit set.
-n string
true if length of string is non-zero.
-o option
true if option named option is on. option may be a
single character, in which case it is a single letter
option name. (See the section `Specifying Options'.)
-p file
true if file exists and is a FIFO special file (named
pipe).
-r file
true if file exists and is readable by current process.
-s file
true if file exists and has size greater than zero.
-t fd
true if file descriptor number fd is open and associ-
ated with a terminal device. (note: fd is not
optional)
-u file
true if file exists and has its setuid bit set.
-w file
true if file exists and is writable by current process.
-x file
true if file exists and is executable by current
process. If file exists and is a directory, then the
current process has permission to search in the direc-
tory.
-z string
true if length of string is zero.
-L file
true if file exists and is a symbolic link.
-O file
true if file exists and is owned by the effective user
ID of this process.
-G file
true if file exists and its group matches the effective
group ID of this process.
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-S file
true if file exists and is a socket.
-N file
true if file exists and its access time is not newer
than its modification time.
file1 -nt file2
true if file1 exists and is newer than file2.
file1 -ot file2
true if file1 exists and is older than file2.
file1 -ef file2
true if file1 and file2 exist and refer to the same
file.
string = pattern
string == pattern
true if string matches pattern. The `==' form is the
preferred one. The `=' form is for backward compati-
bility and should be considered obsolete.
string != pattern
true if string does not match pattern.
string =~ regexp
true if string matches the regular expression regexp.
If the option RE_MATCH_PCRE is set regexp is tested as
a PCRE regular expression using the zsh/pcre module,
else it is tested as a POSIX extended regular expres-
sion using the zsh/regex module. Upon successful
match, some variables will be updated; no variables are
changed if the matching fails.
If the option BASH_REMATCH is not set the scalar param-
eter MATCH is set to the substring that matched the
pattern and the integer parameters MBEGIN and MEND to
the index of the start and end, respectively, of the
match in string, such that if string is contained in
variable var the expression `${var[$MBEGIN,$MEND]}' is
identical to `$MATCH'. The setting of the option
KSH_ARRAYS is respected. Likewise, the array match is
set to the substrings that matched parenthesised subex-
pressions and the arrays mbegin and mend to the indices
of the start and end positions, respectively, of the
substrings within string. The arrays are not set if
there were no parenthesised subexpresssions. For exam-
ple, if the string `a short string' is matched against
the regular expression `s(...)t', then (assuming the
option KSH_ARRAYS is not set) MATCH, MBEGIN and MEND
are `short', 3 and 7, respectively, while match, mbegin
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User Commands ZSHMISC(1)
and mend are single entry arrays containing the strings
`hor', `4' and `6, respectively.
If the option BASH_REMATCH is set the array
BASH_REMATCH is set to the substring that matched the
pattern followed by the substrings that matched paren-
thesised subexpressions within the pattern.
string1 < string2
true if string1 comes before string2 based on ASCII
value of their characters.
string1 > string2
true if string1 comes after string2 based on ASCII
value of their characters.
exp1 -eq exp2
true if exp1 is numerically equal to exp2. Note that
for purely numeric comparisons use of the ((...))
builtin described in the section `ARITHMETIC EVALUA-
TION' is more convenient than conditional expressions.
exp1 -ne exp2
true if exp1 is numerically not equal to exp2.
exp1 -lt exp2
true if exp1 is numerically less than exp2.
exp1 -gt exp2
true if exp1 is numerically greater than exp2.
exp1 -le exp2
true if exp1 is numerically less than or equal to exp2.
exp1 -ge exp2
true if exp1 is numerically greater than or equal to
exp2.
( exp )
true if exp is true.
! exp
true if exp is false.
exp1 && exp2
true if exp1 and exp2 are both true.
exp1 || exp2
true if either exp1 or exp2 is true.
Normal shell expansion is performed on the file, string and
pattern arguments, but the result of each expansion is
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User Commands ZSHMISC(1)
constrained to be a single word, similar to the effect of
double quotes. Filename generation is not performed on any
form of argument to conditions. However, pattern metachar-
acters are active for the pattern arguments; the patterns
are the same as those used for filename generation, see zsh-
expn(1), but there is no special behaviour of `/' nor ini-
tial dots, and no glob qualifiers are allowed.
In each of the above expressions, if file is of the form
`/dev/fd/n', where n is an integer, then the test applied to
the open file whose descriptor number is n, even if the
underlying system does not support the /dev/fd directory.
In the forms which do numeric comparison, the expressions
exp undergo arithmetic expansion as if they were enclosed in
$((...)).
For example, the following:
[[ ( -f foo || -f bar ) && $report = y* ]] && print File exists.
tests if either file foo or file bar exists, and if so, if
the value of the parameter report begins with `y'; if the
complete condition is true, the message `File exists.' is
printed.
EXPANSION OF PROMPT SEQUENCES
Prompt sequences undergo a special form of expansion. This
type of expansion is also available using the -P option to
the print builtin.
If the PROMPT_SUBST option is set, the prompt string is
first subjected to parameter expansion, command substitution
and arithmetic expansion. See zshexpn(1).
Certain escape sequences may be recognised in the prompt
string.
If the PROMPT_BANG option is set, a `!' in the prompt is
replaced by the current history event number. A literal `!'
may then be represented as `!!'.
If the PROMPT_PERCENT option is set, certain escape
sequences that start with `%' are expanded. Many escapes
are followed by a single character, although some of these
take an optional integer argument that should appear between
the `%' and the next character of the sequence. More com-
plicated escape sequences are available to provide condi-
tional expansion.
SIMPLE PROMPT ESCAPES
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Special characters
%% A `%'.
%) A `)'.
Login information
%l The line (tty) the user is logged in on, without
`/dev/' prefix. If the name starts with `/dev/tty',
that prefix is stripped.
%M The full machine hostname.
%m The hostname up to the first `.'. An integer may fol-
low the `%' to specify how many components of the host-
name are desired. With a negative integer, trailing
components of the hostname are shown.
%n $USERNAME.
%y The line (tty) the user is logged in on, without
`/dev/' prefix. This does not treat `/dev/tty' names
specially.
Shell state
%# A `#' if the shell is running with privileges, a `%' if
not. Equivalent to `%(!.#.%%)'. The definition of
`privileged', for these purposes, is that either the
effective user ID is zero, or, if POSIX.1e capabilities
are supported, that at least one capability is raised
in either the Effective or Inheritable capability vec-
tors.
%? The return status of the last command executed just
before the prompt.
%_ The status of the parser, i.e. the shell constructs
(like `if' and `for') that have been started on the
command line. If given an integer number that many
strings will be printed; zero or negative or no integer
means print as many as there are. This is most useful
in prompts PS2 for continuation lines and PS4 for
debugging with the XTRACE option; in the latter case it
will also work non-interactively.
%d
/ Current working directory. If an integer follows the
`%', it specifies a number of trailing components of
the current working directory to show; zero means the
whole path. A negative integer specifies leading com-
ponents, i.e. %-1d specifies the first component.
%~ As %d and %/, but if the current working directory
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User Commands ZSHMISC(1)
starts with $HOME, that part is replaced by a `~'. Fur-
thermore, if it has a named directory as its prefix,
that part is replaced by a `~' followed by the name of
the directory, but only if the result is shorter than
the full path; see Dynamic and Static named directories
in zshexpn(1).
%h
%! Current history event number.
%i The line number currently being executed in the script,
sourced file, or shell function given by %N. This is
most useful for debugging as part of $PS4.
%I The line number currently being executed in the file
%x. This is similar to %i, but the line number is
always a line number in the file where the code was
defined, even if the code is a shell function.
%j The number of jobs.
%L The current value of $SHLVL.
%N The name of the script, sourced file, or shell function
that zsh is currently executing, whichever was started
most recently. If there is none, this is equivalent to
the parameter $0. An integer may follow the `%' to
specify a number of trailing path components to show;
zero means the full path. A negative integer specifies
leading components.
%x The name of the file containing the source code cur-
rently being executed. This behaves as %N except that
function and eval command names are not shown, instead
the file where they were defined.
%c
%.
%C Trailing component of the current working directory.
An integer may follow the `%' to get more than one com-
ponent. Unless `%C' is used, tilde contraction is per-
formed first. These are deprecated as %c and %C are
equivalent to %1~ and %1/, respectively, while explicit
positive integers have the same effect as for the lat-
ter two sequences.
Date and time
%D The date in yy-mm-dd format.
%T Current time of day, in 24-hour format.
%t
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%@ Current time of day, in 12-hour, am/pm format.
%* Current time of day in 24-hour format, with seconds.
%w The date in day-dd format.
%W The date in mm/dd/yy format.
%D{string}
string is formatted using the strftime function. See
strftime(3) for more details. Various zsh extensions
provide numbers with no leading zero or space if the
number is a single digit:
%f a day of the month
%K the hour of the day on the 24-hour clock
%L the hour of the day on the 12-hour clock
The GNU extension that a `-' between the % and the for-
mat character causes a leading zero or space to be
stripped is handled directly by the shell for the for-
mat characters d, f, H, k, l, m, M, S and y; any other
format characters are provided to strftime() with any
leading `-', present, so the handling is system depen-
dent. Further GNU extensions are not supported at
present.
Visual effects
%B (%b)
Start (stop) boldface mode.
%E Clear to end of line.
%U (%u)
Start (stop) underline mode.
%S (%s)
Start (stop) standout mode.
%F (%f)
Start (stop) using a different foreground colour, if
supported by the terminal. The colour may be specified
two ways: either as a numeric argument, as normal, or
by a sequence in braces following the %F, for example
%F{red}. In the latter case the values allowed are as
described for the fg zle_highlight attribute; see Char-
acter Highlighting in zshzle(1). This means that
numeric colours are allowed in the second format also.
%K (%k)
Start (stop) using a different bacKground colour. The
syntax is identical to that for %F and %f.
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%{...%}
Include a string as a literal escape sequence. The
string within the braces should not change the cursor
position. Brace pairs can nest.
A positive numeric argument between the % and the { is
treated as described for %G below.
%G Within a %{...%} sequence, include a `glitch': that is,
assume that a single character width will be output.
This is useful when outputting characters that other-
wise cannot be correctly handled by the shell, such as
the alternate character set on some terminals. The
characters in question can be included within a %{...%}
sequence together with the appropriate number of %G
sequences to indicate the correct width. An integer
between the `%' and `G' indicates a character width
other than one. Hence %{seq%2G%} outputs seq and
assumes it takes up the width of two standard charac-
ters.
Multiple uses of %G accumulate in the obvious fashion;
the position of the %G is unimportant. Negative inte-
gers are not handled.
Note that when prompt truncation is in use it is advis-
able to divide up output into single characters within
each %{...%} group so that the correct truncation point
can be found.
CONDITIONAL SUBSTRINGS IN PROMPTS
%v The value of the first element of the psvar array
parameter. Following the `%' with an integer gives
that element of the array. Negative integers count
from the end of the array.
%(x.true-text.false-text)
Specifies a ternary expression. The character follow-
ing the x is arbitrary; the same character is used to
separate the text for the `true' result from that for
the `false' result. This separator may not appear in
the true-text, except as part of a %-escape sequence.
A `)' may appear in the false-text as `%)'. true-text
and false-text may both contain arbitrarily-nested
escape sequences, including further ternary expres-
sions.
The left parenthesis may be preceded or followed by a
positive integer n, which defaults to zero. A negative
integer will be multiplied by -1. The test character x
may be any of the following:
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User Commands ZSHMISC(1)
! True if the shell is running with privileges.
# True if the effective uid of the current process
is n.
? True if the exit status of the last command was n.
_ True if at least n shell constructs were started.
C
/ True if the current absolute path has at least n
elements relative to the root directory, hence /
is counted as 0 elements.
c
.
~ True if the current path, with prefix replacement,
has at least n elements relative to the root
directory, hence / is counted as 0 elements.
D True if the month is equal to n (January = 0).
d True if the day of the month is equal to n.
g True if the effective gid of the current process
is n.
j True if the number of jobs is at least n.
L True if the SHLVL parameter is at least n.
l True if at least n characters have already been
printed on the current line.
S True if the SECONDS parameter is at least n.
T True if the time in hours is equal to n.
t True if the time in minutes is equal to n.
v True if the array psvar has at least n elements.
V True if element n of the array psvar is set and
non-empty.
w True if the day of the week is equal to n (Sunday
= 0).
%<string<
%>string>
%[xstring]
Specifies truncation behaviour for the remainder of the
prompt string. The third, deprecated, form is equiva-
lent to `%xstringx', i.e. x may be `<' or `>'. The
numeric argument, which in the third form may appear
immediately after the `[', specifies the maximum per-
mitted length of the various strings that can be dis-
played in the prompt. The string will be displayed in
place of the truncated portion of any string; note this
does not undergo prompt expansion.
The forms with `<' truncate at the left of the string,
and the forms with `>' truncate at the right of the
string. For example, if the current directory is
`/home/pike', the prompt `%8<..<%/' will expand to
`..e/pike'. In this string, the terminating character
(`<', `>' or `]'), or in fact any character, may be
quoted by a preceding `\'; note when using print -P,
however, that this must be doubled as the string is
zsh 5.0.5 Last change: January 5, 2014 41
User Commands ZSHMISC(1)
also subject to standard print processing, in addition
to any backslashes removed by a double quoted string:
the worst case is therefore `print -P "%<\\\\<<..."'.
If the string is longer than the specified truncation
length, it will appear in full, completely replacing
the truncated string.
The part of the prompt string to be truncated runs to
the end of the string, or to the end of the next
enclosing group of the `%(' construct, or to the next
truncation encountered at the same grouping level (i.e.
truncations inside a `%(' are separate), which ever
comes first. In particular, a truncation with argument
zero (e.g. `%<<') marks the end of the range of the
string to be truncated while turning off truncation
from there on. For example, the prompt '%10<...<%~%<<%#
' will print a truncated representation of the current
directory, followed by a `%' or `#', followed by a
space. Without the `%<<', those two characters would
be included in the string to be truncated.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | shell/zsh |
+---------------+------------------+
|Stability | Volatile |
+---------------+------------------+
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from http://down-
loads.source-
forge.net/project/zsh/zsh/5.0.5/zsh-5.0.5.tar.bz2
Further information about this software can be found on the
open source community website at http://www.zsh.org/.
zsh 5.0.5 Last change: January 5, 2014 42