use strict;
my $str = '1er couplet:
Gm G
Mon enfant, nue sur les galets
G D7
Le vent dans tes cheveux defaits
Dsus Cmaj
Comme un printemps sur mon trajet
C Em
Un diamant tombé d\'un coffret';
my $regex = qr/(\b(?:G,C,D|A,B,C|E,C,D)|(?:[ABCDEFG](?:#|b)?)(?:\/[ABCDEFG]b)?(?:(?:(?:maj|min|sus|add|aug|dim)(?:\d{0,2}(?:#\d{1,2}|sus\d)?)?)|(?:m\d{0,2}(?:(?:maj|add|#)\d{0,2})?)|(?:-?\d{0,2}(?:\([^)]*\)|#\d{1,2})?))?)/p;
my $subst = '[${1}]';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html