Hello,

I am trying to write some perl code to search for a pattern in a file, if i found the pattern, i want to comment (put a #before the line) it out.

Is it possible through perl.

Something like this.


#!/usr/bin/perl -w

open(FILE,"test.txt") or die "Unable to open file\n";

while(<FILE>) {
my $line =$_;
if ($line =~ /Hello/) {
print "Match found: $line\n";
s/$line/#$line/;
}
}

i think you have the right idea. whenever im manipulating a file like this, i read one in (read only) and create a new one (write only), ive never used the same file for read/write (replacing) like you want to do, but it can be done either way of course. the only real thing your missing is writing the line to the file. a simple print statement is all you need. however, i would write it using the following pseudocode:

in either case (whether the line matched the pattern or not), the line is still written to the output/new/modified file. does this help?

You could do it as a one liner as well, something like

perl -pi -e '$_ = "#".$_ if m/Hello/;' input_file.txt

it does the edit in place by renaming the input file and opening an new output file with the original name


[edit, cleaner one liner]
perl -pi -e 'print "#" if m/Hello/;' input_file.txt