Search and replace with an expression

If it takes me longer than five minutes or so to remember something or to look it up, I’ll probably blog it.

I wanted to expand character ranges like ‘a-z’ into their explicit ‘abcdefghijklmnopqrstuvwxyz’ versions, and I wanted to do it in a single regexp. I figured this would need a call to a subroutine to do the actual expansion, but couldn’t remember how to get the regexp to do that. I wasted a fair bit of time reading the stuff about (?{ code }) expressions in the perlre man page, but that’s for running arbitrary code on the left-hand side, in the pattern to be matched.

What really I wanted was the /e flag, which makes the right-hand side evaluate as Perl:

    $string =~ s/([^\\])-(.)/expandpair($1, $2)/eg;