Re: Issue with regex matching

you can escape the special chars stored in the variable $constant using \Q and \E. See also perlre.

     if($_ =~ m/^(\Q$constant\E)/) {
       $line_count++;
     }
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Since $constant is user specified you could simply call quotemeta on the user input before using it. Then you won't need \Q and \E in your regex. E.g.:

my $searchterm = quotemeta $user_input;
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You are currently only counting lines which start with that pattern. You wrote that you wanted to count all occurrences of the pattern. If you want to match all the occurrences of $constant per line you could change your code to:

     while ($_ =~ m/\Q$constant\E/gc) {
       $count++; 
     }
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Other thoughts:

use lexical filehandles (open my $FILE ... instead of open FILE)
$constant doesn't seem like a fitting variable name to me. How about $searchterm?
in case you only open the file to look for $constant: don't loop through the file if $constant is empty/undef. You currently have the check _within_ the while (<FILE>) loop. So even if you don't have a valid searchterm you are still looping through the entire file.

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Re^2: Issue with regex matching by AnomalousMonk (Archbishop) on Aug 29, 2013 at 00:46 UTC
`while ($_ =~ m/\Q$constant\E/gc) { $count++; }` [download] Minor point: in `m/\Q$constant\E/gc` the `/c` modifier is unnecessary, although it does no harm in this instance... ... although wanna_code_perl's `$count += () = /\Q$constant\E/g;` in a readline loop or `$count = () = /\Q$constant\E/g;` on a slurped file is, IMHO, better.	[reply] [d/l] [select]
Re^2: Issue with regex matching by sowais (Sexton) on Aug 29, 2013 at 21:40 UTC
Thanks for your input rminner. Adding the \Q and \E as you stated worked. I will try with quotemeta as well. I admit I could have done a better job in explaining the objective, I need to count the number of lines where the $constant variable appears in the file. For the points you mentioned under 'Other thoughts': - I do use something like $FILE in the code but to make the code more easy on the eyes I simply inserted the code where the problem was occurring. - Its a line counter script that I am converting from batch, and to keep things consistent for the users, I kept the same terminology. I do agree term could use a change. - I am doing something else if $constant is empty/undef, that part is working properly so thought there is no sense in copying all of that. Thanks Again!	[reply]