Explain output produced by Regexp::Assemble

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

Dear Monks,

I am learning perl. When I use a Regexp::Assemble module i have a little bit doubt.

I Created Regexp for the following:

use Regexp::Assemble;
my $ra=Regexp::Assemble->new;
$ra->add('Text.');
$ra->add('TEXT.');
$ra->add('Texts');
print $ra->re;
[download]

I got the output

(?-xism:T(?:EXT.|ext.))
[download]

Please teach me what is mean by ?-xism:

Thank You

Retitled by g0n from 'Regexp::Assemble'.

Comment on Explain output produced by Regexp::Assemble Select or Download Code

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Re: Explain output produced by Regexp::Assemble by polypompholyx (Chaplain) on Aug 03, 2005 at 08:50 UTC
They're the same as the x (extended space-insensitive), i (case insensitive), s (single line, allow `.` to match `\n`.), and m (multi line, allow `^` and `$` to match around `\n`) modifiers you can put on the end of a regex `m//` match. When you save a modified regex using quote-regex (which Regex::Assemble uses internally), like this `$regex = qr/foo/ix`, these flags need to be set within the `$regex`, particularly because you might well incorporate it into a larger quoted regex at some later point, like this: `$fwibble = qr/$regex\|something_else/`. The flags are only in operation for the first part of this new regex, but not for `something_else`. The flags ahead of the dash are the ones in operation within the scope of the enclosing parentheses. So `(?-xism:foo)` means that none of the flags are in operation when trying to match 'foo'. `(?misx:foo)` would mean all of them are in operation, and `(?ix-sm:foo)` would mean only i and x were.	[reply] [d/l] [select]
Re: Explain output produced by Regexp::Assemble by umbra (Acolyte) on Aug 03, 2005 at 07:44 UTC
As far as I understand pattern ?:something means something is a pattern to be tested for. -xism is just re engine parameters, described in perlre	[reply]
Re^2: Explain output produced by Regexp::Assemble by tlm (Prior) on Aug 03, 2005 at 11:44 UTC
As far as I understand pattern ?:something means something is a pattern to be tested for. Not quite. What you quoted is incomplete. It should be `(?:something)` [download] and it tells the regex engine that the parentheses should be used only for grouping, and not for capturing a submatch in one of `$1`, `$2`, etc. the lowliest monk	[reply] [d/l] [select]