c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = 'this is the path/to/my/file what i want';
 ;;
 my $rx_ptf = qr{ \w+ (?: / \w+)+ }xms;
 ;;
 print qq{matched: '$1'} if $s =~ m{ \b ($rx_ptf) \b }xms;
"
matched: 'path/to/my/file'
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The  qr// m// s/// delimiters are (more or less) arbitrary. (Update: Please see Regexp Quote-Like Operators in perlop.)