#!/usr/bin/perl

#/****************************************************************************\
#|                                                                            |
#| Bryce Alcock                                                               |
#| This Script will read each line a file, and will conditionally do the      |
#| following:                                                                 |
#|      If the line starts with $ARGV[1]  (the second argument).              |
#|         it will print the line as is, and then it will                     |
#|         copy the line replacing all occurances of $ARGV[1] with $ARGV[2].  |
#|      If the line does not start with $ARGV[1], it will print the line.     |
#|                                                                            |
#| Example:                                                                   |
#|                                                                            |
#| MatchDupReplace.pl inputFile.txt YY  XY                                    |
#|                                                                            |
#| inputFile.txt:                                                             |
#|                                                                            |
#| YY  banana YY Apple YY YC.                                                 |
#| YP  banana YP Apple YY YD.                                                 |
#|                                                                            |
#| OUTPUT:                                                                    |
#|                                                                            |
#| YY  banana YY Apple YY YC.                                                 |
#| XY  banana XY Apple XY YC.                                                 |
#| YP  banana YP Apple YY YD.                                                 |
#|                                                                            |
#| WHAT IS THIS GOOD FOR:                                                     |
#| I use this to conditionally double the number and variety of input         |
#| lines for various load test scripts.                                       |
#|                                                                            |
#| This can also be used as a building block for more complex replacement     |
#| Conditionals.                                                              |
#\****************************************************************************/


#  ARGV[0] is the file we are processing.
$File = $ARGV[0];
#  Keep track of the number of lines read in,
#  and the number of lines printed out.
$linesIN = 0;
$linesOUT = 0;

#  ARGV[1] is the pattern to match.
#  ARGV[2] is the replacement string.
$pattern=$ARGV[1];
$replacement=$ARGV[2];

open(FILE,"+< $File");
    $out='';
	while($line =<FILE>){
        $linesIN++;
		#  NOTE: that the ^ means the line will only match if $pattern 
		#        is at the front of the $line.
	    if($line =~ /^$pattern/){
            $linesOUT+=2;
			# print the original line.
            print "$line";
			# I make a copy of the original here for clarity.
			# a more efficeint version would just modify in place.
            $newline = $line;
            $newline =~ s/$pattern/$replacement/g;
			# print the modified line.
            print "$newline";
	    }else{
            $linesOUT+=1;
            print "$line";
        }
    }
    print "\n\n\tLines IN: $linesIN linesOUT $linesOUT!\n";  
close(FILE) or die "can't close $File $!";