Not matching a single quote (apostrophe!)

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

I have a large tab-delimited data file:

e.g.

Town\tCounty
Westminster\tGreater London
King's Cross\tGreater London
Mayfair (north)\tGreater London
Mayfair (south)\tGreater London
...
[download]

what i am doing is a count of some things, then adding a value to each list item;

Town\tCounty\tVALUE
[download]

love perl for how easy this (generally) is;

$tmp=(get the file contents);
$tmp=~s/\r//g;
$tmp="\n$tmp\n";

($n,$v)=[got from somewhere, same as list items]
($ctr)=[got from somewhere else]
($rctr)=[count of replacements made]

## attempt 1

if ($tmp=~/^$n\t$v$/) {          
   $tmp=~s/^$n\t$v$/$n\t$v\t$ctr/;
   $rctr++;
} else {

....
[download]

THE PROBLEM is that if $n contains brackets () or a single quote ', then it doesn't match. Now, the following fixes the brackets, it matches fine, BUT NOT THE QUOTE. I cannot match or replace the list items with single quotes (apostrophes):

# attempt 2

   $n=~s/\(/\\(/g;    ## << this works ok!
   $n=~s/\)/\\)/g;
   $n=~s/\'/\\'/g;    ## << same method, NO WORK!</font>

   if ($tmp=~/^$n\t$v$/) {
    $tmp=~s/^$n\t$v$/$n\t$v\t$ctr/;
        $gctr++;
   }
[download]

How do i fix this? Anyone? Help gratefully appreciated!

Comment on Not matching a single quote (apostrophe!) Select or Download Code

Replies are listed 'Best First'.
Re: Not matching a single quote (apostrophe!) by moritz (Cardinal) on Nov 17, 2009 at 13:37 UTC
Using `\Q$n\E` in the regex instead of just `$n` should solve your problem. See perlre and quotemeta. If it doesn't, please supply a short example by giving us the contents of the variables `$tmp` and `$n` at the point where it fails. Perl 6 - links to (nearly) everything that is Perl 6.	[reply] [d/l] [select]
Re^2: Not matching a single quote (apostrophe!) by puddleglum (Initiate) on Nov 17, 2009 at 14:03 UTC
Yes, I tried \Q$n\E but still fails $tmp contains some 27,000 lines, the entries with quotes fail e.g. King's Cross\tGreater London $n is exactly "King's Cross", for attempt 1, "King\'s Cross" for attempt 2. Note the brackets "Mayfair (north)" won't work in attempt 1 but will work in attempt 2 if I match "Mayfair $north$" so why not the quote????	[reply]
Re^3: Not matching a single quote (apostrophe!) by moritz (Cardinal) on Nov 17, 2009 at 14:40 UTC
`$tmp contains some 27,000 lines, the entries with quotes fail` Then extract a line that should match, and doesn't, and show us that line. Perl 6 - links to (nearly) everything that is Perl 6.	[reply] [d/l]
Re: Not matching a single quote (apostrophe!) by JavaFan (Canon) on Nov 17, 2009 at 14:06 UTC
BUT NOT THE QUOTE Since a quote is not special regexp character, it doesn't need escaping. If a quote gives you a problem, you have to look elsewhere than trying to escape it in the regexp: that's not the problem. From the snippit you give us, I cannot determine where a quote makes a difference. Or is the given quote a different quote than you are matching against? (Someone gives you a "smart" quote for instance, which you're trying to match against an ASCII quote?)	[reply]
Re^2: Not matching a single quote (apostrophe!) by puddleglum (Initiate) on Nov 17, 2009 at 14:24 UTC
>> Since a quote is not special regexp character, it doesn't need escaping. agreed!! >> Or is the given quote a different quote than you are matching against? (Someone gives you a "smart" quote for instance ... ) yeah! hate smart quotes! the data file has been 'cleaned' to ensure there are no such entities. The quote character used in the replace was cut-and-pasted and globally-replaced in the data file and my perl, so it is definitely, 100%, exactly the same!	[reply]
Re: Not matching a single quote (apostrophe!) by przemo (Scribe) on Nov 17, 2009 at 13:38 UTC
Take a look at \Q and \E escapes, which allow to turn off special chars in a regexp.	[reply]
Re: Not matching a single quote (apostrophe!) by puddleglum (Initiate) on Nov 17, 2009 at 14:43 UTC
Ok ppl, thanks for the inspiration Have now fixed it, for some reason; `$tmp=s/\n$n\t$v/\n$n\t$v\t$ctr/` will work on non-escaped quote ' as opposed to; `$tmp=s/^$n\t$v/$n\t$v\t$ctr/` or even; `$tmp=s/$n\t$v/$n\t$v\t$ctr/` Which both failed. I am sure I tried this before my jeckling with \' n \Q's n \E's, but maybe not. Thanks ppl!	[reply] [d/l] [select]
Re^2: Not matching a single quote (apostrophe!) by ikegami (Patriarch) on Nov 17, 2009 at 16:00 UTC
"^" matches the start of the string. Sounds like you want to match the start of the line. Use the /m modifier to make "^" match the start of the line. Your question had nothing to do with single quotes. perlre	[reply]
Re^3: Not matching a single quote (apostrophe!) by puddleglum (Initiate) on Nov 18, 2009 at 00:07 UTC
quite right! obvious when you look at it..	[reply]