#!/usr/bin/perl

use strict;

my $var = 1;
print "$var\n";



open (IN, "test.pl");
my @lines = <IN>;
close (IN);

open (OUT, ">temp.pl");

foreach (@lines) {
    if ($_ =~ /^my \$var = /) {
        my @parts = split (/\s+/, $_);
        printf OUT "my \$var = %i;\n", ++$parts[@parts - 1]
    } else {
        print OUT $_;
    }
}

close (OUT);
system ("mv temp.pl test.pl");