qr can do it as perlre syntax allows (?i) the same as /i

$ perl -le " print int q{shoes} =~ /SHOES/ "
0

$ perl -le " print int q{shoes} =~ /SHOES/i "
1

$ perl -le " print int q{shoes} =~ /(?i)SHOES/ "
1
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App::Ack uses this trick

You can use eval { no re qw/eval/; qr/$regex/ }; to see if the regex compiles

See also Text::Glob#glob_to_regex