my $eq = sub { $_[0] == $_[1] };
my $lt = sub { $_[0] <  $_[1] };
# ...

while (<>) {
    $num ="2";
    if ( ...some logic... ) {
         $op = $eq;
    }
    else {
         $op = $lt;
    }
    $eq = sub { $_[0] == $_[1] };
    /(\d+).*/;
    if ($op->( $num, $1 ) ) {
        print "match\n";
    }
}