Re^7: how to remove a string from end of a line

Well, here's a hint to get you started:

c:\@Work\Perl\monks>perl -wMstrict -le
"use YAPE::Regex::Explain;
 ;;
 print YAPE::Regex::Explain->new(qr{ (?: [|] [^|]*){4} \z }xms)->expla
+in;
"
The regular expression:

(?msx-i: (?: [|] [^|]*){4} \z )

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?msx-i:                 group, but do not capture (with ^ and $
                         matching start and end of line) (with .
                         matching \n) (disregarding whitespace and
                         comments) (case-sensitive):
----------------------------------------------------------------------
  (?:                      group, but do not capture (4 times):
----------------------------------------------------------------------
    [|]                      any character of: '|'
----------------------------------------------------------------------
    [^|]*                    any character except: '|' (0 or more
                             times (matching the most amount
                             possible))
----------------------------------------------------------------------
  ){4}                     end of grouping
----------------------------------------------------------------------
  \z                       the end of the string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

But it's difficult to answer questions you haven't asked. Again, please see perlre, perlretut, and perlrequick. (In particular, perlretut has a lot of info. And all this on-line documentation is available at your local command line via perldocperlretut and etc.) Also, please see the articles in the Pattern Matching, Regular Expressions, and Parsing section of the Monastery Tutorials; some of them may address your questions. All this stuff is free, but there are some good book$ out there if you want some recommendations. davido has a nice regex exerciser; see his personal node for a link. I and others will be very happy to answer your questions, but please try to make them as specific as possible.

Give a man a fish: <%-{-{-{-<

Comment on Re^7: how to remove a string from end of a line Select or Download Code

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Re^8: how to remove a string from end of a line by ravi45722 (Pilgrim) on Oct 12, 2015 at 11:53 UTC
I started reading "perlretut". But I struck "?:" here. I cant understand that explanation. In the document I see this example. `$x = '12aba34ba5'; @num = split /(a\|b)+/, $x; # @num = ('12','a','34','a','5') print @num,$/; @num = split /(?:a\|b)+/, $x; # @num = ('12','34','5') print @num,$/;` [download] Based on the regex explained earlier in the document I can write that code like this. `@num = split /[ab]+/, $x; # @num = ('12','34','5') print @num,$/;` [download] But I want to know how that "?:" working in the regex. Thanks for reply	[reply] [d/l] [select]
Re^9: how to remove a string from end of a line by choroba (Cardinal) on Oct 12, 2015 at 12:23 UTC
`(?:...)` works like `(...)`, but doesn't create a capture group (e.g. $1). split returns separators if they're captured, so if you need grouping but don't need the separators, `(?:...)` becomes handy. لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l] [select]
Re^9: how to remove a string from end of a line by AnomalousMonk (Archbishop) on Oct 12, 2015 at 19:37 UTC
I agree that `/(a\|b)+/` is better written as `/[ab]+/` in the general case. But `/(a\|b)+/` was only intended to exemplify the difference between capturing and non-capturing groups in the split built-in function. Note that `a` and `b` in the `(a\|b)` expression could represent any regex expression, not just the literal characters `'a'` and `'b'`. That's not true in a character class, which can only be composed of literal characters or another character class, e.g., `\s` or `\w`. See perlrecharclass. ... how that "?:" working in the regex. The `(?`symbol(s) `...)` syntax was introduced with Perl version 5.10 to support a multitude of regular expression extensions. The `(?` sequence was never valid in regexes prior to 5.10, so it was a convenient vehicle for these extensions. So you have `(?: non-capturing group)` `(?> atomic group)` `(?= positive look-ahead)` `(?<! negative look-behind)` `etc.` See Extended Patterns in perlre. See perlre and perlretut for info on the differences between capturing and non-capturing groups. See also Special Backtracking Control Verbs for a similar syntactic twist: `(*` was never valid pre-5.10. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^10: how to remove a string from end of a line by ravi45722 (Pilgrim) on Oct 13, 2015 at 05:15 UTC
Now its getting very clear. The example you wrote to remove last 4 is `$s =~ s{ (?: [\|] [^\|]){4} \z }{}xms;` and can be written also as `$s =~ s{ ( [\|] [^\|]){4} \z }{}xms;` But if we don't need $1 values we can use "?:". As you advised I read "perlretut". From that I understand the "\z" used to indicate the end of the line and "ms" used for detecting multiple lines and "\n". And the "x" is used for increasing the readability of code in regex using spaces	[reply] [d/l] [select]