The numeric variables ($1 etc.) are only set on the right hand side of a substitution. You need to use the corresponding backreference (e.g. \1) on the LHS of a s/// or in a m//. See perlretut and perlre, the former of which uses this exact problem as its example.

In reply to Re: Recognizing duplicates by Fletch
in thread Recognizing duplicates by b4swine

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