#!/usr/bin/perl -w
use strict;
die "usage: $0 <file> <search pattern> <replace pattern>",
    unless @ARGV == 3;
my $searchFile = $ARGV[0];
my $searchPattern = $ARGV[1];
my $replacePattern = $ARGV[2];
my $tempFile = 'tmp$$';
open FILE, $searchFile  #opens file in read-only mode
        or die "Cannot open $searchFile in read-only mode. $!\n";
open TMP, '>'.$tempFile
        or die "Cannot create temp file. $!\n";

while (<FILE>) {
    chomp;
    if (/$searchPattern/i) {
    print "Match found...replacing at line $.\n";
    $_ =~ s/$searchPattern/$replacePattern/i;
    print TMP $_."\n";
    }else {
    print TMP $_."\n"
    }
}
close FILE;
close TMP;
unlink $searchFile;
rename $tempFile, $searchFile;
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