Stringification of a compiled regex produces something that can be used in other qr//, m// or s/// without changing the meaning of the pattern. Adding (?^:...) or similar is necessary to achieve that.

my $re = qr/a/;

say "a" =~ /$re/    || 0;   # 1
say "A" =~ /$re/    || 0;   # 0
say "a" =~ /$re/i   || 0;   # 1
say "A" =~ /$re/i   || 0;   # 0

my $pat1 = "(?^:a)";

say "a" =~ /$pat1/  || 0;   # 1
say "A" =~ /$pat1/  || 0;   # 0
say "a" =~ /$pat1/i || 0;   # 1
say "A" =~ /$pat1/i || 0;   # 0

my $pat2 = "a";

say "a" =~ /$pat2/  || 0;   # 1
say "A" =~ /$pat2/  || 0;   # 0
say "a" =~ /$pat2/i || 0;   # 1
say "A" =~ /$pat2/i || 0;   # 1  XXX
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That said, you can get the unmodified pattern (and the flags) using re's re::regexp_pattern.

my ( $pat, $flags ) = re::regexp_pattern( $re );
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You can rebuild the original compiled regex using the following:

my $re = eval "no re; qr/\$pat/$flags";
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