Regarding 
{4|8}

[download]
this is a nice idea, but doesn't do anything special. a curly bracket is only a special character when it is found in one of these forms {n}, {n,} or {n,m}.

As your example isn't like this, the bracket is just matched as a plain character. What your first regex shows is just an alternation, equivalent to the following... 

if (/[0-9a-f]\{4/ or /8\}/} {
  print "matched\n";
}

[download]
Note that I've escaped the curly bracket just to be explict, it's not actually necessary
---
my name's not Keith, and I'm not reasonable.

In reply to Re: what means this regex? $x = qr/[0-9a-f]{4|8}/ by reasonablekeith
in thread what means this regex? $x = qr/[0-9a-f]{4|8}/ by kidongrok

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