Your solution looks very close to a common trick I use, which is to assign a vairable to another variable, then do a regex search and replace on the new one: 

my $file = 'file013.txt';
(my $sk = $file) =~ s/^.*?(\d+).*$/$1/;

[download]

Which for the sake of this problem is a very similar solution to what others are proposing, the above method is much more useful when I want to keep most of the string rather than a portion of it.

Example, I want to emphasise the word keep above: 

my $boring_string = '...when I want to keep most of the string...';
(my $exciting_string = $boring_string) =~ s/(keep)/<b>$1</b>/;

[download]

elbieelbieelbie

In reply to (elbie): Regex not behaving as expected by elbie
in thread Regex not behaving as expected by Popcorn Dave

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