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]

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

(?:...) 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

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:  <%-{-{-{-<