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a2p (1)


a2p - Awk to Perl translator


a2p [options] [filename]


Perl Programmers Reference Guide                           A2P(1)

     a2p - Awk to Perl translator

     a2p [options] [filename]

     A2p takes an awk script specified on the command line (or
     from standard input) and produces a comparable perl script
     on the standard output.

     Options include:

          sets debugging flags.

          tells a2p that this awk script is always invoked with
          this -F switch.

          specifies the names of the input fields if input does
          not have to be split into an array.  If you were
          translating an awk script that processes the password
          file, you might say:

                  a2p -7

          Any delimiter can be used to separate the field names.

          causes a2p to assume that input will always have that
          many fields.

     -o   tells a2p to use old awk behavior.  The only current
          differences are:

          o    Old awk always has a line loop, even if there are
               no line actions, whereas new awk does not.

          o    In old awk, sprintf is extremely greedy about its
               arguments.  For example, given the statement

                       print sprintf(some_args), extra_args;

               old awk considers extra_args to be arguments to
               "sprintf"; new awk considers them arguments to

     A2p cannot do as good a job translating as a human would,

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Perl Programmers Reference Guide                           A2P(1)

     but it usually does pretty well.  There are some areas where
     you may want to examine the perl script produced and tweak
     it some.  Here are some of them, in no particular order.

     There is an awk idiom of putting int() around a string
     expression to force numeric interpretation, even though the
     argument is always integer anyway.  This is generally
     unneeded in perl, but a2p can't tell if the argument is
     always going to be integer, so it leaves it in.  You may
     wish to remove it.

     Perl differentiates numeric comparison from string
     comparison.  Awk has one operator for both that decides at
     run time which comparison to do.  A2p does not try to do a
     complete job of awk emulation at this point.  Instead it
     guesses which one you want.  It's almost always right, but
     it can be spoofed.  All such guesses are marked with the
     comment ""#???"".  You should go through and check them.
     You might want to run at least once with the -w switch to
     perl, which will warn you if you use == where you should
     have used eq.

     Perl does not attempt to emulate the behavior of awk in
     which nonexistent array elements spring into existence
     simply by being referenced.  If somehow you are relying on
     this mechanism to create null entries for a subsequent, they won't be there in perl.

     If a2p makes a split line that assigns to a list of
     variables that looks like (Fld1, Fld2, Fld3...) you may want
     to rerun a2p using the -n option mentioned above.  This will
     let you name the fields throughout the script.  If it splits
     to an array instead, the script is probably referring to the
     number of fields somewhere.

     The exit statement in awk doesn't necessarily exit; it goes
     to the END block if there is one.  Awk scripts that do
     contortions within the END block to bypass the block under
     such circumstances can be simplified by removing the
     conditional in the END block and just exiting directly from
     the perl script.

     Perl has two kinds of array, numerically-indexed and
     associative.  Perl associative arrays are called "hashes".
     Awk arrays are usually translated to hashes, but if you
     happen to know that the index is always going to be numeric
     you could change the {...} to [...].  Iteration over a hash
     is done using the keys() function, but iteration over an
     array is NOT.  You might need to modify any loop that
     iterates over such an array.

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Perl Programmers Reference Guide                           A2P(1)

     Awk starts by assuming OFMT has the value %.6g.  Perl starts
     by assuming its equivalent, $#, to have the value %.20g.
     You'll want to set $# explicitly if you use the default
     value of OFMT.

     Near the top of the line loop will be the split operation
     that is implicit in the awk script.  There are times when
     you can move this down past some conditionals that test the
     entire record so that the split is not done as often.

     For aesthetic reasons you may wish to change index variables
     from being 1-based (awk style) to 0-based (Perl style).  Be
     sure to change all operations the variable is involved in to

     Cute comments that say "# Here is a workaround because awk
     is dumb" are passed through unmodified.

     Awk scripts are often embedded in a shell script that pipes
     stuff into and out of awk.  Often the shell script wrapper
     can be incorporated into the perl script, since perl can
     start up pipes into and out of itself, and can do other
     things that awk can't do by itself.

     Scripts that refer to the special variables RSTART and
     RLENGTH can often be simplified by referring to the
     variables $`, $& and $', as long as they are within the
     scope of the pattern match that sets them.

     The produced perl script may have subroutines defined to
     deal with awk's semantics regarding getline and print.
     Since a2p usually picks correctness over efficiency.  it is
     almost always possible to rewrite such code to be more
     efficient by discarding the semantic sugar.

     For efficiency, you may wish to remove the keyword from any
     return statement that is the last statement executed in a
     subroutine.  A2p catches the most common case, but doesn't
     analyze embedded blocks for subtler cases.

     ARGV[0] translates to $ARGV0, but ARGV[n] translates to
     $ARGV[$n-1].  A loop that tries to iterate over ARGV[0]
     won't find it.

     A2p uses no environment variables.

     Larry Wall <>


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Perl Programmers Reference Guide                           A2P(1)

     See attributes(5) for descriptions of the following

     |Availability   | runtime/perl-512 |
     |Stability      | Uncommitted      |
      perl   The perl compiler/interpreter

      s2p    sed to perl translator

     It would be possible to emulate awk's behavior in selecting
     string versus numeric operations at run time by inspection
     of the operands, but it would be gross and inefficient.
     Besides, a2p almost always guesses right.

     Storage for the awk syntax tree is currently static, and can
     run out.

     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

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