Re^9: how to remove a string from end of a line

[AnomalousMonk]

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.

[ravi45722]

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