Converting Awk Script to Perl Script - Examples of a2p Unix Command

Unix provides the a2p (awk to perl) utility for converting the awk script to perl script. The a2p command takes an awk script and produces a comparable perl script.

Syntax of a2p:

a2p [options] [awk_script_filename]

Some of the useful options that you can pass to a2p are:

-D<number>     Sets debugging flags.
-F<character>  This will tell a2p that awk script is always invoked with -F option.
-<number>       This makes a2p to assume that input will always have the specified number of fields.

For more options see the man pages; man a2p

Example 1:

The awk script which prints the squares of numbers up to 10 is shown below. Call the below script as awk_squares.

#!/bin/awk -f
BEGIN 
{
    for (i=1; i <= 10; i++) 
    {
        print "The square of ", i, " is ", i*i;
    }
exit;
}

Run this script using awk command; awk -f awk_squares. This will produce squares of numbers up to 10.

Now we will convert this script using the a2p as
a2p awk_squares > perl_squares

The content of converted perl script, perl_squares, is shown below:

#!/usr/bin/perl
eval 'exec /usr/bin/perl -S $0 ${1+"mailto:$@%22%7D'
if $running_under_some_shell;
# this emulates #! processing on NIH machines.
# (remove #! line above if indigestible)
eval '$'.$1.'$2;' while $ARGV[0] =~ /^([A-Za-z_0-9]+=)(.*)/ && shift;
# process any FOO=bar switches
$, = ' ';               # set output field separator
$\ = "\n";              # set output record separator

for ($i = 1; $i <= 10; $i++) {
    print 'The square of ', $i, ' is ', $i * $i;
}
last line;

Run the perl script as: perl perl_squares. This will produce the same result as the awk.

Example 2:

We will see an awk script which prints the first field from a file. The awk script for this is shown below. Call this script at awk_first_field.

#!/bin/awk -f
{
    print $1;
}

Run this script using awk command by passing a file as input: awk -f awk_first_field file_name. This will prints the first field of each line from the file_name.

We will convert this awk script into per script using the a2p command as
a2p awk_first_field > perl_first_field

The content of converted perl script, perl_first_field, is shown below:

#!/usr/bin/perl
eval 'exec /usr/bin/perl -S $0 ${1+"mailto:$@%22%7D'
if $running_under_some_shell;
# this emulates #! processing on NIH machines.
# (remove #! line above if indigestible)
eval '$'.$1.'$2;' while $ARGV[0] =~ /^([A-Za-z_0-9]+=)(.*)/ && shift;
# process any FOO=bar switches
$, = ' ';               # set output field separator
$\ = "\n";              # set output record separator
while (<>) {
    ($Fld1) = split(' ', $_, -1);
    print $Fld1;
}

Now run the perl script as: perl perl_first_field file_name. This will produce the same result as awk command.