see get n lines before or after a pattern, Re: modifying a file with regex!, perlintro, open, readline, rename, Re^5: Remove a Line, perlintro, open, close, readline, rename, Re: Rewriting into file, @ARGV, Getopt::Long, Re^2: Write to existing file with character insert

Modifying an existing file is three steps :)

1. read old file
2. create a new file
3. rename new file to name of old file

perlintro covers all three steps, as does Modern Perl and http://learn.perl.org/books/beginning-perl/

Path::Tiny makes it even easier to work with paths

I have started writing the script to open a file and parse through the lines.but iam troubling with pattern matching and insert the words in the resulting line.

open my $file ,"+<","reg" or die $!;

while (my $line = <$file>) {

  chomp $line;
  print "$line\n"

  }
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I have started writing the script to open a file and parse through the lines.but iam troubling with pattern matching and insert the words in the resulting line.

Ok then, then look here :)

The questions need help in writing aperl script and Re^2: need help in writing aperl script will be a lot easier to understand if you use markup (code and para tags). See the instructions at the text entry box and/or Markup in the Monastery.

And you'll profit by reading (carefully!) On asking for help, How do I post a question effectively? and Writeup Formatting Tips.