more info about regex updates

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

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Re: more info about regex updates by ikegami (Patriarch) on Oct 20, 2010 at 19:32 UTC
Lots of regex ops start with "(?". The most common of which is grouping ("(?:...)"): `/ab\|cd/` [download] will match `ab` [download] and `cd` [download] while `/a(?:b\|c)d/` [download] will match `abd` [download] and `acd` [download] perlre	[reply] [d/l] [select]
Re: more info about regex updates by Anonymous Monk on Oct 20, 2010 at 17:50 UTC
always perlre	[reply]
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Re: more info about regex updates by halfcountplus (Hermit) on Oct 20, 2010 at 19:01 UTC
? is used in lookahead/lookbehind expressions: http://www.regular-expressions.info/lookaround.html	[reply]
Re^2: more info about regex updates by Anonymous Monk on Oct 20, 2010 at 19:17 UTC
named capture buffers, like `(?<NAME>pattern)` and then `$+{NAME}` instead of `$1`	[reply] [d/l] [select]
Re^3: more info about regex updates by halfcountplus (Hermit) on Oct 20, 2010 at 19:29 UTC
Oh yay, something new & unknown! Will correct post.	[reply]
Re: more info about regex updates by aquarium (Curate) on Oct 20, 2010 at 22:15 UTC
using the question mark as a quantity qualifier following a character or expression denotes 0 or 1 of those. perl has extensions to the standard regular expressions on systems with sed/awk/grep etc. quite a few of those extensions in perl regex start with a question mark inside brackets. non-greedy matching is with *? quantifier, nothing to do with the previous construct. sometimes you have to be careful with the non-greedy match, as it can also match the zero-width nothingness before the next match, if the next match can eat up the prior characters. the \1 \2 \3 etc match replacements are part of original (unix utilities) regular expression syntax, and are being phased out in perl, in favor of $1 $2 $3 etc. this is because the legacy syntax is only maximum 9 match replacements, i.e. \1 thru \9. all of these things are departures (extensions) to original (unix) regular expression syntax, and have been with us since perl 5.6 or 5.8. most of the extensions are typically not necessary in a lot of typical day to day work, and hence not widely known/used. it's pretty nice though to come from a unix background to learn perl, and find out that 99% of standard regex syntax applies. a good understanding of even the standard regular expression syntax is a good asset to have. the hardest line to type correctly is: stty erase ^H	[reply]