perl -p -i.bak -w -e 's/dude/Johnny5/g' myinfo.txt

##</code><code>##

LINE:
    while (<>) {
	...		# your program goes here
    } continue {
	print or die "-p destination: $!\n";
    }

##</code><code>##

#!/usr/bin/perl -w

$extension = '.bak';

LINE:
    while (<>) {
        if ($ARGV ne $oldargv) {
            if ($extension !~ /\*/) {
                $backup = $ARGV . $extension;
            } else {
                ($backup = $extension) =~ s/\*/$ARGV/g;
            }

            rename($ARGV, $backup);
            open(ARGVOUT, ">$ARGV");
            select(ARGVOUT);
            $oldargv = $ARGV;
        }

	s/dude/Johnny5/g;
    } continue {
        print or die "-p destination: $!\n";
    }