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NAME    [Toc]    [Back]

       a2p - Awk to Perl translator

SYNOPSIS    [Toc]    [Back]

       a2p [options] filename

DESCRIPTION    [Toc]    [Back]

       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    [Toc]    [Back]

       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              -nlogin.password.uid.gid.gcos.shell.home

            Any delimiter can be used to separate the field

            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

       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

       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    [Toc]    [Back]

       A2p uses no environment variables.

AUTHOR    [Toc]    [Back]

       Larry Wall <larry@wall.org>

FILES SEE ALSO    [Toc]    [Back]

        perl   The perl compiler/interpreter
        s2p    sed to perl translator

DIAGNOSTICS BUGS    [Toc]    [Back]

       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.

perl v5.8.5                 2002-11-06                          4
[ Back ]
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