In python, I can abuse capture group names in a substitution to simplify the substitution code, like: 
$ python -c 'import regex; print(regex.sub("^(?<a>.)|(?<c>.)$|(?<b>.)"
+, lambda m:m.lastgroup, "xxx"))'
abc

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In perl, if there is a single variable equivalent to lastgroup, I can't find it, the closest I see is %+: 
$ perl -E'say "xxx" =~ s/^(?<a>.)|(?<c>.)$|(?<b>.)/@{[keys %+]}/gr'
abc

[download]
which isn't awful, but is there a better way I'm missing?

A math joke: r = | |csc(θ)|+|sec(θ)| |-| |csc(θ)|-|sec(θ)| |

In reply to better way to get last named capture group by ysth

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