#!/usr/bin/perl -w
# written by andrewt@cse.unsw.edu.au as a COMP2041 example
# For each file given as argument replace occurrences of Hermione
# allowing for some misspellings with Harry and vice-versa.
# Relies on Zaphod not occurring in the text.
# Modified text is stored in a new file
# which is then renamed to replace the old file

foreach $filename (@ARGV) {
    $tmp_filename = "$filename.new";
    die "$0: $tmp_filename already exists" if -e "$tmp_filename";
    open my $f, '<', $filename or die "$0: Can not open $filename: $!";
    open my $g, '>', $tmp_filename or die "$0: Can not open $tmp_filename : $!";
    while ($line = <$f>) {
        $line =~ s/Herm[io]+ne/Zaphod/g;
        $line =~ s/Harry/Hermione/g;
        $line =~ s/Zaphod/Harry/g;
        print $g $line;
    }
    close $f;
    close $g;
    rename "$tmp_filename", $filename or die "$0: Can not rename file";
}