Feel free to save this source code into a file of your own to try out and/or experiment with.

#!/usr/bin/perl -w

#  Here's a small program that can be used to search for a string
#  in a file or file(s).  You just invoke the program from the
#  command line with the file(s) you want to search like this:
#
#     ./searchfor.pl  file
#
#  The program will then prompt you for a string for which to search,
#  and then will search all lines of the file(s) for that string,
#  printing lines that match (i.e. include the string as a substring).
#  Note that the search is done ignoring the case of the letters.
#
#  (This program is a very, very basic "grep"-like search program, but
#  not very sophisticated at all.)

use strict;

   my ($str, );

   print "\nEnter search string:  ";

   chomp ( $str = <STDIN> );
   print "\n";

   #  search all the lines of the file(s)
   while (<>)
      {
         if ( /${str}/i )   #  Look for a match, ignoring case.
                            #  This is how you use a variable name
                            #  in a regular expression.  The "i" option
                            #  tells the regular expression engine to
                            #  ignore case.  
            {   print;   }
      }

   print "\n";