This does what you want

$url = 'http://www.fubar.com/fileXXX.txt';

# name and extension
($file) = $url =~ m|^.*/(.*)$|;
print "$file\n";

# if you want the name without the extension
$ext ='txt';
($file) = $url =~ m|^.*/(.*)\.$ext$|o;
print "$file\n";
[download]

Note with the second RE you can hard code in $ext if you want. The o at the end is a compile once directive It make the regex faster but means that if you change $ext on the fly this regex will not care! Just remove the o if you need to do this.

cheers

tachyon