


A2P(1)           Perl Programmers Reference Guide          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".






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A2P(1)           Perl Programmers Reference Guide          A2P(1)


            "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 exis-
            tence 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 sim-
            plified 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



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A2P(1)           Perl Programmers Reference Guide          A2P(1)


            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 oper-
            ation that is implicit in the awk script.  There are
            times when you can move this down past some condi-
            tionals 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 sub-
            str() 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 com-
            mon 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.



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A2P(1)           Perl Programmers Reference Guide          A2P(1)


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 select-
       ing 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.






































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