regex problem with metachars

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

I've run into a problem with a script I'm developing that among other things changes a delimited files delimiter, 1st checking that the new delimiter does not exist in the data.
Everything works fine unless the delimiter is a regex metacharacter. So if the delimiter is ":" no problem, but if the delimiter is a "|" big problem as the expresion /$n_delim/ is always true when $n_delim =~ /|/
I've tried several approaches but they've all failed as I won't know what the delimiter may be. Most often though the delimiter would be "," or "|" or "\t". I been banging my head against the wall for days with this and I just can't figure it out. The snippet below is from the offending script. For those of you wondering; I do have use strict; and use warnings; at the top.

open(FI, "<", $i_file) or die "Unable to open $i_file: $!";
while (sysread(FI, $_, 2 ** 16)){  
    if (/$n_delim/){
        print "Delimiter: $n_delim already in $i_file\n";
        exit 2;
    }
}
[download]

Thanks in advance!

Comment on regex problem with metachars Download Code

Replies are listed 'Best First'.
Re: regex problem with metachars by shenme (Priest) on Nov 07, 2003 at 18:04 UTC
Use \Q and \E surrounding your possibly offending characters. This will 'quote' any strange and nasty characters by escaping them with '\'. Read about these in perlre.	[reply]
Re: Re: regex problem with metachars by sweetblood (Prior) on Nov 07, 2003 at 18:33 UTC
Thanks for your reply but, but by using \Q it also would put a splash in front of any escaped character such as "\t". The same goes for quotemeta().	[reply]
Re: Re: Re: regex problem with metachars by sgifford (Prior) on Nov 07, 2003 at 18:47 UTC
That's because `\t` is a regex metacharacter. If you only want to escape some metacharacters, you'll need to figure out which ones. If you want to escape all metacharacters beside backslash, something like: `s/([^A-Za-z_0-9\\])/\\$1/g;` [download] should do it.	[reply] [d/l] [select]
Re: Re: Re: regex problem with metachars by tedrek (Pilgrim) on Nov 07, 2003 at 18:53 UTC
If the delimiter will always be one character then you can assume anything longer than 1 character is a escape sequence like "\t". So you just call quotemeta() on delimiters with a length of 1. HTH Tedrek	[reply]
Re: Re: Re: Re: regex problem with metachars by sweetblood (Prior) on Nov 07, 2003 at 19:21 UTC
Re: regex problem with metachars by ptkdb (Monk) on Nov 07, 2003 at 18:07 UTC
Have you tried the quotemeta function?	[reply]
Re: regex problem with metachars by injunjoel (Priest) on Nov 08, 2003 at 01:43 UTC
Greetings, Here are my thoughts on the current dilema. Are you sure you want to do this test with regex? I think index() might better serve your needs. So the line in your original post `if (/$n_delim/){` [download] would be rewritten as `if (index($_, $n_delim) != -1){` [download] Seeing as you are not doing anything regexp specific with the value of $n_delim. Hope that helps... Peace and blessings to you all -injunjoel	[reply] [d/l] [select]


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