Refer by relative way to regex group (eg. the last one)

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

How to refer by relative way e.g. to get the last regex group from Perl code inserted inside regex, as

'foobar' =~ /(oo)(bar)(?{$word=${-1}})/
[download]

fails, word var. can't be bar ?

Comment on Refer by relative way to regex group (eg. the last one) Download Code

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Re: Refer by relative way to regex group (eg. the last one) by LanX (Saint) on Jan 19, 2022 at 01:22 UTC
You may wanna try the two possibilities listed in `perlretut` and `perlvar` You got those links already last time you asked. Additionally has `perlre` even a demo similar to your code. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply]
Re^2: Refer by relative way to regex group (eg. the last one) by RMGir (Prior) on Jan 19, 2022 at 14:28 UTC
The \g{-1} syntax is interesting, I don't recall that one. When did it come about? (Of course, it's possible it's been around since Perl 4 and I just missed it :) ) Mike	[reply]
Re^3: Refer by relative way to regex group (eg. the last one) by Fletch (Bishop) on Jan 19, 2022 at 14:41 UTC
Looks like 5.10 according to perl5100delta: `Relative backreferences A new syntax "\g{N}" or "\gN" where "N" is a decimal integer a +llows a safer form of back-reference notation as well as allowing re +lative backreferences. This should make it easier to generate and emb +ed patterns that contain backreferences. See "Capture buffers" in perlre. (Yves Orton)` [download] The cake is a lie. The cake is a lie. The cake is a lie.	[reply] [d/l]
Re^3: Refer by relative way to regex group (eg. the last one) by Corion (Patriarch) on Jan 19, 2022 at 14:40 UTC
Grepping the `perldelta*` files for \\g lists perl5100delta, so likely the feature was introduced with Perl 5.10.0.	[reply] [d/l]
Re^3: Refer by relative way to regex group (eg. the last one) by choroba (Cardinal) on Jan 19, 2022 at 14:44 UTC
Syntax::Construct to the rescue :-) `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l]
Re^3: Refer by relative way to regex group (eg. the last one) by LanX (Saint) on Jan 19, 2022 at 14:35 UTC
> When did it come about? I don't know, but the OP wants $vars which can be used inside Perl code. (which is also documented in multiple ways) Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery} update see Re^2: Refer by relative way to regex group (eg. the last one)	[reply]
Re^3: Refer by relative way to regex group (eg. the last one) by Anonymous Monk on Jan 19, 2022 at 16:00 UTC
Perl 5.9.5 if you want to be picky.	[reply]
Re: Refer by relative way to regex group (eg. the last one) by Anonymous Monk on Jan 19, 2022 at 16:10 UTC
You do not say how your code fails, but if you add `use strict;` to your example you get $ perl -Mstrict -Mwarnings -e 'my $word; "foobar" =~ /(oo)(bar)(?{$word=${-1}})/' Can't use string ("-1") as a SCALAR ref while "strict refs" in use at -e line 1. Suggestions: $ perldoc -v '@-' $ perldoc -v '@+' Or, under at least Perl 5.10, you could use named captures.	[reply] [d/l]
Re^2: Refer by relative way to regex group (eg. the last one) by LanX (Saint) on Jan 19, 2022 at 17:14 UTC
> Suggestions: sigh... $+ aka `$LAST_PAREN_MATCH` $^N aka `$LAST_SUBMATCH_RESULT` @{^CAPTURE} Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery} update `DB<29> "ab" =~ /^((.)(.))(?{say $+;say $^N; say "$1 $2 $3\n@{^CAPTUR +E}"})/ b ab ab a b ab a b` [download]	[reply] [d/l] [select]

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