[0-9] matches exactly one digit, so the first match is f1 and $1 is 1. There's no such hash key, so it interpolates undef, which stringifies to the empty string.

It would help to write ([0-9]+) or ([0-9]{3}), depending on what your data looks like.

Perl 6 - second systems done right

In reply to Re: problem with substitute in regexp by moritz
in thread problem with substitute in regexp by upaksh

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