#!/usr/bin/perl -w

    use strict;

    #define TRACE(x) print "$0 line ". __LINE__ .":\t". x ." = ". eval(x). "\n";

    my $foo = 7;
    TRACE('$foo');

    $foo *= $foo;
    TRACE('$foo');

    __END__
    Prints:

    /tmp/test.pl line 8:   $foo = 7
    /tmp/test.pl line 11:  $foo = 49