local our $length;
$x =~ /(\d+)(?{ $length = length($1) })$/;

[download]

or in Perl 5.8: 

local our $length;
$x =~ /(\d+)(?{ $length = length($^N) })$/;

[download]

In reply to Re: Length of first captured match by ikegami
in thread Length of first captured match by QM

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