In this snippet it looks like the /m modifier does not modify a regex if it came from a pre-compiled regex. (4th print is 0). If I am not mistaken this was not always like this. I think in 5.8.x the 4th print still printed 1. Can you confirm this? Can someone point me to the explanation of this?
use strict;
use warnings;
my $str = "x\nab\ny";
my $re = '^ab$';
print $str =~ /$re/ ? 1 : 0, "\n"; # 0
print $str =~ /$re/m ? 1 : 0, "\n"; # 1
my $qre = qr/^ab$/;
print $str =~ /$qre/ ? 1 : 0, "\n"; # 0
print $str =~ /$qre/m ? 1 : 0, "\n"; # 0 but I think 5.8.x still had
+ this as 1
Update
Thanks for all the responses and links!