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A2P(1)
NAME
  a2p - Awk to Perl translator

SYNOPSIS
  a2p [options] filename

DESCRIPTION
  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

  Options include:

  -D<number>
       sets debugging flags.

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

  -n<fieldlist>
       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 -nlogin.password.uid.gid.gcos.shell.home

       Any delimiter can be used to separate the field names.

  -<number>
       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:

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

       ·    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 "print".

  "Considerations"

  A2p cannot do as good a job translating as a human would, 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 for...in, 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.

  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 the array base $[ from 1 back
  to perl's default of 0, but remember to change all array subscripts AND all
  substr() and index() operations to match.

  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].  A loop
  that tries to iterate over ARGV[0] won't find it.

ENVIRONMENT
  A2p uses no environment variables.

AUTHOR
  Larry Wall <larry@wall.org>

FILES
SEE ALSO
   perl	  The perl compiler/interpreter

   s2p	  sed to perl translator

DIAGNOSTICS
BUGS
  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.

Index for Section 1

Alphabetical listing for A

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