#! /usr/bin/perl

# パスの指定
$pathname1 = "/directory/filename.txt";
$pathname2 = "C:\\Directory\\filename.txt";

if( $pathname1 =~ m|.*/(.*)$|i ) {
   $filename1 = $1;
}

if( $pathname2 =~ m/.*\\(.+)$/i ) {
   $filename2 = $1;
}

# 表示
print $filename1 . "\n";
print $filename2 . "\n";

exit;