Negative Lookahead using negated character classes?

Wonko the sane has asked for the wisdom of the Perl Monks concerning the following question:

Hello,

Here is what I am trying to do.

if ( m|/user/(?!prot/)| )
[download]

The problem is I cannot use negative lookahead to do it.

To do this, I have tried the following variations with no success.

#!/usr/local/bin/perl5.6.0 -w
use strict;

while ( <DATA> )
{
    chomp;

    #if ( m|/user/(?!prot/)| )      # Works
    #if ( m|/user/[^p]?[^r]?[^o]?[^t]?[^/]?| )
    #if ( m|/user/([^p]*?[^r]*?[^o]*?[^t]*?[^/]*?)?| )
    #if ( m|/user/[^p]+?[^r]+?[^o]+?[^t]+?[^/]+?| )
    #if ( m|/user/([^p]*[^r]*[^o]*[^t]*[^/]*)?| )
    {
        print qq{Disallow!! [$_]\n};
    }
    else
    {
        print qq{Allowed. [$_]\n};
    }
}

__DATA__
/user/prot/
/user/protrusions/
/user/a/
/user/backups
[download]

The only one that I want to print "Allowed", (not to match) is the first one "/user/prot/".

OT: Why cant I use negative lookahead?

Actually because I am trying to make a regex for an Apache LocationMatch section,
to disable some settings for all directories inside a users site, except for one,
'/user/prot'.
The regex engine in Apache though does not have lookaround assertion ability :(.

<LocationMatch  /user/(?!prot/) >
   <Limit GET>
         order allow,deny
         deny from all
    </Limit>
    AllowOverride None
</LocationMatch>
[download]

Any help is much appreciated.

Wonko

Comment on Negative Lookahead using negated character classes? Select or Download Code

Replies are listed 'Best First'.
Re: Negative Lookahead using negated character classes? (\|) by tye (Sage) on Oct 28, 2003 at 17:07 UTC
`m#/usr/(prot([^/]\|$)\|pro([^t]\|$)\|pr([^o]\|$)\|p([^r]\|$)\|[^p]\|$)#` (updated) - tye	[reply] [d/l]
Re: Negative Lookahead using negated character classes? by pg (Canon) on Oct 28, 2003 at 17:32 UTC
regexp is challenging and fun, but not always the best solution, sometime it could be ugly and not maintainable. In this case, first split on /, to get the prot part, then use the power of bitwise XOR like this (I choose not to use natural language to descibe, you should be able to understand what I am trying to say): `use strict; my $str = "paat"; (my $cmp = $str ^ "prot") =~ s/(.)/ord($1) ? "0" : "1"/eg; print $cmp; #prot => 1111 #pro? => 1110 #pr?? => 1100 #p??? => 1000 #???? => 0000` [download]	[reply] [d/l]
Re: Negative Lookahead using negated character classes? by delirium (Chaplain) on Oct 28, 2003 at 21:04 UTC
Not Perl, but why not do something like: `<LocationMatch /user/> <Limit GET> order allow,deny deny from all </Limit> AllowOverride None </LocationMatch> <LocationMatch /user/prot/> Override all the stuff above </LocationMatch>` [download]	[reply] [d/l]
Re: Negative Lookahead using negated character classes? by BrowserUk (Patriarch) on Oct 28, 2003 at 22:22 UTC
Doesn't this do what you want? `#! perl -slw use strict; while ( <DATA> ) { chomp; if ( $_ !~ m[/user/prot/$] ) { print qq{Disallow!! [$_]}; } else { print qq{Allowed. [$_]}; } } __DATA__ /user/prot/ /user/protrusions/ /user/a/ /user/backups` [download] Output `P:\test>test2 Allowed. [/user/prot/] Disallow!! [/user/protrusions/] Disallow!! [/user/a/] Disallow!! [/user/backups]` [download] Examine what is said, not who speaks. "Efficiency is intelligent laziness." -David Dunham "Think for yourself!" - Abigail Hooray!	[reply] [d/l] [select]
Re: Negative Lookahead using negated character classes? by ptkdb (Monk) on Oct 28, 2003 at 17:21 UTC
by implication, you seem to be using perl 5.6.0. That's a bit out of date isn't it?	[reply]
Re: Negative Lookahead using negated character classes? by Abigail-II (Bishop) on Oct 28, 2003 at 17:10 UTC
Actually because I am trying to make a regex for an Apache LocationMatch section What has that to do with Perl? If everyone is going to ask his or her non-Perl language questions here, it's going to be hard to find the interesting questions. Abigail	[reply]
Re: Re: Negative Lookahead using negated character classes? by shaq the foo (Initiate) on Oct 29, 2003 at 19:03 UTC
Because we use apache to render our perl apps. So stop being a sniveling little biotch. BTW is this the same abigail that gave the boring, emotionless, half ass tutorial at the last YAPC at F.A.U?	[reply]


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