Whitout this it is impossible to guess what you are triyng to achieve.

Probably a single regex can do the job you need. Here around are very good regexer (not me).

Do not modify your original post without putting some note on changes: replies can have no sense after the modification of the original post.

L*

Hello,

First of all, sorry for providing insufficient information about my problem. I understand now, that I need to explain my problem clearly for me to get some help.

OK. Here goes..

I am trying to find a few strings (stored in array) from about 50,000 lines of code in a file. After finding, I'm doing some changes to the matched strings and writing it to another file. To accomplish this task, I'm assigning 5 regexes to five variables.

foreach my $ur (@strings_to_be_matched)
{
     $reg1 = qr/\=/i;
     $reg2 = qr/\S+\=\S+/i;            
     $reg3 = qr/extern.+\b$ur\b\s*/i;
     $reg4 = qr/;$/i;                       
     $reg5 = qr/.+\b$ur\b\s*/i;

     foreach my $line (@contents_of_file)
{

     if(($ln =~ $reg3 and $ln =~ $reg4)){
     <some code>
     }

     if(($ln =~ $reg5 and $ln=~ $reg4 and ($ln !~ $reg1 or $ln =~ $reg
+2))
     {
     <some code>
     }
     

     if(($ln =~ $reg3 and $ln !~ $reg4)){
     <some code>
     }

     if(($ln =~ $reg5 and $ln !~ $reg4 and $ln !~ $reg1))
     {
     <some code>
     }

   }

}
[download]

I'm using "qr" to pre-compile my regexes, so that I can reduce the time taken. I feel $reg5 is causing the problem here. The if conditions which involve $reg5 take longer time to match.

if (($ln =~ $reg5 and $ln=~ $reg4 and ($ln !~ $reg1 or $ln =~ $reg2)))
{
<some code here...>
}

if (($ln =~ $reg5 and $ln !~ $reg4 and $ln !~ $reg1)) 
{
<some code here...>
}
[download]

Another point to be noted is that, there are a few lines in the file which have a length of about ~12000. These lines take 4 seconds each to be processed.I want to reduce the time taken as few seconds taken to process each line are adding up to ~30 minutes. This is not acceptable at all in my case.

Reduce the problematic code to a short stand alone example that shows the problem. See I know what I mean. Why don't you? for tricks to include sample data. If you need a lot of data, get the test script to generate it.

We don't need to see your sensitive code or data, but we can't help much with hand wavy descriptions of the problem. We need a good representation of the structure of the code to be able to give good advice.