Re: Regex matching a string beginning with "root: " but not containing another string

It can be done with just a standard regexp, but it's monumentally ugly. If you want to match "root:" not followed by "bar", you get

/root:                #need root
 ($                   #it could end there
 |([^b]               #if not, first letter isn't b
  |b($|[^a]           #or it can be b if it's not 
    |a($|[^r])        #followed by ar
/x
[download]

(Untested, I may have gotten it a little wrong.) Suffice to say, it's ugly, but it's doable. You just have to make sure that you always allow either the end of the string ($), any single character but the next, or the next character, as long as it itself isn't followed by (the rest of the string). Writing that for something long and complicated is a nightmare (unless someone has written a script to do it, which I don't know of).

Comment on Re: Regex matching a string beginning with "root: " but not containing another string Download Code

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Re^2: Regex matching a string beginning with "root: " but not containing another string by jryan (Vicar) on Sep 09, 2004 at 20:08 UTC
Here's a different way to do it. IMHO, the regex it produces will be much easier and make much more sense. `use strict; my $email = "myself\@domain.of-my.own"; my $string = "root: myself\@domain.of-my.own"; my $re = inv_str_seq($email); $string =~ /^root: $re/ and print 1; sub inv_str_seq { my($string) = @_; my @c = map { quotemeta($_) } split '', $string; my $re = "\n [^$c[0]] \n"; $re .= " \| " . join('',@c[0..$_-1]) . " [^$c[$_]]\n" for (1 .. $#c); $re = qr/$re/x; return qr/$re+ (?:[^$c[0]]\|$)/x; }` [download] Update: Moved the quotemeta up.	[reply] [d/l]
Re^2: Regex matching a string beginning with "root: " but not containing another string by Roy Johnson (Monsignor) on Sep 09, 2004 at 19:26 UTC
Here's a little sub to generate such a regex from the string you want not to match: `sub not_string_regex { my $str = shift; my $reg; for(0..length($str)-1) { my $let = substr($str,$_,1); $reg .= '($\|[^'.$let.']\|'.$let; } substr($reg, -2) = ''; $reg .= ')' x length($str); }` [download] Caution: Contents may have been coded under pressure.	[reply] [d/l]