I dare to disagree for global substitutions s///g

Either it doesn't match, so the error can't occur with a tested regex!

Or one used or clauses or conditional matching like in /(a)|(b)(c)/ then having an undefined $2 is intended behaviour.

in the latter case silencing the warning of an undefined value becoming an empty string is the normal approach. ( no warnings qw/uninitialized/ )

Cheers Rolf
(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!

In reply to Re^2: On error, how to show the regexp values? by LanX
in thread Tracing warnings: how to show the regexp values? by nikolay

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