use strict;
use warnings;

my $old="welcome|to|chennai";
my $new="Capital of karnataka|is|bangalore";

  my $base = ();
  my @base = ();
my $file="c:/users/jeyakuma/desktop/search.txt";
    open(BASE, $file) || die("Could not open file!");
    @base=<BASE>;
    close (BASE);

      foreach $base(@base)
        {
          if($base =~ /$old/){
             $base =~ s/$old/$new/gi;
             print ("Replaced!\n");
          }
  open (BASE, ">$file");
  print BASE @base;
  close (BASE);
    };