OPEN file1
READ contents of file1 into array @words

OPEN file2
FOR line in file 2
    IF line contains any of @words
        PRINT "#" + line
    ELSE
        PRINT line
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My idea: read the first file, build a regex from all lines (by joining the lines with |), then read the second file, and prepend a # to all lines which match the regex.

(It's easier if you first produce the correct output instead of editing the file in-place).

Your answer can be found by using Search (above) or Super Search, as your question is a minor variation on one that comes up again and again.

This is how my program looks like now. I tried this but the grep here is not returning right value, its returning 1 as if its matching all the time.

#!/usr/bin/perl -w
open(MATCH_PATTERN,"< temp1");
open(FILE_TO_LOOK,"< temp2");
open OF, "> temp3";

while ($m =<MATCH_PATTERN>)
{
print "reading the current text to match \n $m \n";
seek (FILE_TO_LOOK ,0, 0);
while ($l= <FILE_TO_LOOK>) {
print "reading the textline to look for match \n $l \n";
@found = grep ($m, $l) ;
$match = @found;
if ($match == 1)
{
print "now the match is \n $match \n";
print OF "#$l";
}

}
}
close FILE_TO_LOOK;
close MATCH_PATTERN;
close OF;

You are misunderstanding the use of grep.

In your example, grep will always return $l unless $m happens to be 0 or an empty string.

Instead of grep, you probably want a regular expression.

  if($l =~ /\Q$m\E/)
  {
     print "We matched\n";
     print OF "$$l";
  }
[download]

You probably also want to use chomp in the outer loop to remove the line ending from $m.

You are also writing the file multiple times with different lines commented each time. You might want to generate a list of the expressions to match at the beginning and then loop over the file once.

G. Wade

#!/usr/bin/perl

use strict;
use warnings;

my @file_a_array;
my $newfile;
my $file_a = <path to word file>;
my $file_b = <path to lines of text>;

open (FILE_A, "$file_a") or die "couldn't open the file!";

while (my $line = <FILE_A>) {
     chomp ($line);
     push (@file_a_array, $line);
}

close (FILE_A);

open (FILE_B, "$file_b") or die "couldn't open the file!";

while (my $line = <FILE_B>) {
     chomp ($line);
     foreach my $word (@file_a_array) {
        if ($line =~ /$word/) {
                $newfile = $newfile . "# ";
        }
     }
     $newfile = $newfile . $line . "\n";
}

close (FILE_B);

open (FILE_B, ">$file_b") or die "couldn't open the file!";
print FILE_B $newfile;
close (FILE_B);

print "end\n";
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Would you mind, if I suggest very small suggestion to your code?

$! will give more information regarding the type of failure



open (FILE_A, "$file_a") or die "couldn't open the file!";
>>open (FILE_A, "$file_a") or die "couldn't open the file $file_a <$!>
+!";
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close function will also fail, its better to check that as well



close (FILE_A);
>>close (FILE_A) or die "Unable to close file";
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Thanks alot. This works exactly how I want. Thanks for all your support.