I think (mostly because I've only been following this thread from the sidelines) that this won't "work" if there is no underscore at the end of the string:

#! /usr/bin/perl -w

use strict;
use locale;

for my $s ( @{[
    "_'nada_komo_el_'sol_",
    "_na'da_komo_el_so'l_",
    "_na'da_komo_el_sol"
]} ) {
    print $s;
    $s =~  s/(_)([^'][^_]+?)/$1'$2/g;
    print " : $s\n";
}

__END__

> perl -w tmp.pl

_'nada_komo_el_'sol_ : _'nada_'komo_'el_'sol_
_na'da_komo_el_so'l_ : _'na'da_'komo_'el_'so'l_
_na'da_komo_el_sol : _'na'da_'komo_'el_'sol

[download]

My solution would be to use a zero-width lookahead to ensure but not match the following underscore:

    $s =~  s/(_)([^_']+?)(?=_)/$1'$2/g;

[download]

... but again, as I haven't been closely following, I'm not sure where my approach will fail the specifications.

In reply to Re^4: Modifying the match position after each match by Corion
in thread Modifying the match position after each match by pat_mc

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