• Check for the success or failure of open and close operations.

• Use the three argument form of open and lexical filehandles.

• Don't keep opening and closeing your output file every time you find a line you are interested in, do them once outside the while loop. Your code keeps opening the file for writing thereby clobbering what you have written in previous loops.

• Add captures to your regex to preserve what comes before and after $element and avoid the performance implications of $'.

• Reading into $_ can save some typing as certain operations default to using $_ if no argument is given.

use strict;
use warnings;

my $element = q{coucou};
my $inFile  = q{EXEMPLE.txt};
my $outFile = qq{RESEARCHED_text_${element}.txt};

open my $inFH, q{<}, $inFile
   or die qq{open: $inFile: $!\n};
open my $outFH, q{>}, $ourFile
   or die qq{open: $outFile: $!\n};

while ( <$inFH> )
{
    next unless m{(.*?)$element(.*);
    print $outFH;
    my $beforeElement = $1;
    my $afterElement  = $2;
    # Do something here with your captured text ...
}

close $inFH
   or die qq{close: $inFile: $!\n};
close $outFH
   or die qq{close: $outFile: $!\n};
[download]

I hope this is of use.

Cheers,

JohnGG

But note that using this variable (as well as $` and $&) slows down the regex engine in the whole program. So read the warnings in perlre and keep them in mind.

Hi steph_bow,

You can get the previous text from the matching string by using '$`' and the following text by using '$'' like,

#!/usr/bin/perl
use strict;
use warnings;

my $element = "coucou";

open (INFILE, "<EXEMPLE.txt");


while (my $line = <INFILE>){
    if ($line =~ /$element/){
            my $pre=$`;###to get the previous text from the matching t
+ext
            my $post=$';###to get the following text from the matching
+ text        
        print "PREVIOUS:$pre\nFOLLOWING:$post\n";
    }
}

close INFILE;
[download]

Punitha

Here is a small snippet of code that demonstrates how this might be done:

#!/usr/bin/perl
use strict;
use warnings;

my $wanted = 'coucou';

while (my $line = <DATA>) {
    chomp($line);
    my $rest = '';
    if ($line =~ m/$wanted(.*)$/) {
        $rest = $1;
        print "$wanted:$rest\n";
    }
    else {
        print "$wanted not found in $line\n";
    }
}

__DATA__
abc coucou def
not in this line
in this line, but nothing following coucou
coucou once, coucou twice, coucou three times - what should be done wi
+th this line?
[download]

One thing you didn't specify in your question is what should happen if the string is found more than once in any line. The example above assumes that you would want everything after the first match.

If you wanted instead, everything after the last match, then you could achieve this by inserting a "greedy" dot-star at the beginning of the pattern match, like so:

m/.*$wanted(.*)$/
[download]

Cheers,
Darren