How to print the qr regex to the stdout?

ovedpo15 has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks!
Really simple question here but can't seem to make it work. As part of a debugging message, I'm trying to print the regex operator which is saved in a var. If I use Data::Dumper, the var looks like (it's a hash where one key is regex):

{
    'regex' => qr/^\/a\/.*?\/b\/.*\/pkgs\/([^\/]*)?\/([^\/]*)?\/.*/
}
[download]

When I print the message:

print("Regex: $regex\n");
[download]

I get:

Regex: ?^:^/nfs/.*?/itools/.*/pkgs/([^\/]*)?/([^\/]*)?/.*/)
[download]

It adds the ?^: at the start. What is the proper way to get rid of it?

Comment on How to print the qr regex to the stdout? Select or Download Code

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Re: How to print the qr regex to the stdout? by ikegami (Patriarch) on Feb 28, 2022 at 17:45 UTC
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` [download] That said, you can get the unmodified pattern (and the flags) using re's `re::regexp_pattern`. `my ( $pat, $flags ) = re::regexp_pattern( $re );` [download] You can rebuild the original compiled regex using the following: `my $re = eval "no re; qr/\$pat/$flags";` [download]	[reply] [d/l] [select]
Re: How to print the original qr regex to the stdout? by Anonymous Monk on Feb 28, 2022 at 10:15 UTC
It adds the ?^: at the start. What is the proper way to get rid of it? Try Data::Dump pp to serialize regex or something from re or B to get original qr maybe use https://perldoc.perl.org/re#regexp_pattern($ref) `my ($pat, $mods) = regexp_pattern($ref); my $parentless = ( $pat =~ m/[^:]+:(.*?)\)$/s )[0];` [download]	[reply] [d/l]
Re^2: How to print the original qr regex to the stdout? by ovedpo15 (Pilgrim) on Feb 28, 2022 at 10:38 UTC
Thank you very much! One question - why the second line is needed? It looks like `$pat` does what I need.	[reply] [d/l]
Re^3: How to print the original qr regex to the stdout? by Anonymous Monk on Feb 28, 2022 at 13:55 UTC
My cell phone doesnt have perl, the doc example implied the (^:) being returned	[reply]
Re^4: How to print the original qr regex to the stdout? (termux) by LanX (Saint) on Feb 28, 2022 at 14:26 UTC
Re: How to print the qr regex to the stdout? by LanX (Saint) on Feb 28, 2022 at 12:12 UTC
On another note: You used a lot of escaping of `\/` in your regex: > `"regex" => qr/^\/a\/.?\/b\/.\/pkgs\/([^\/])?\/([^\/])?\/./`* Are you aware that `qr` and his siblings of "quote-like-operators" allow other delimiters? Like `qr(...)` or `qr~...~` and so on? Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]