... $1 is not available when the RHS is evaluated.

Just as a side note, it's worse. Captures from a previous successful match are available: 

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"'keep your powder dry' =~ /(pow)/;
 ;;
 $_ = 'a_b_c';
 ;;
 my %h;
 $h{ (/a_(.*)_c/)[0] } = qq{boom_$1};
 ;;
 dd \%h;
"
{ b => "boom_pow" }

[download]
And we glimpse the protean form of a nasty bug.

Give a man a fish:  <%-{-{-{-<

In reply to Re^2: do something if hash keys match regex by AnomalousMonk
in thread do something if hash keys match regex by anandk

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