addFifthLine

#!/usr/bin/perl
#
# addFifthLine
#
# Parse an HTML file formatted according to the MIT Shakespeare format,
# and print every fifth line number at the end of the line.
#
# Input: an HTML file using the MIT Shakespeare Format
# Output: that same file, but with every fifth line printed after the line.
#
# Add the following to the <head> element of your resulting HTML file to
# offset the line numbers to the right of the text. You may need to increase
# or decrease the left offset (default is 550px).
#
# <style type="text/css">
# .lineNum {
#  position: absolute;
#  left: 550px;
# }
# </style>

use strict;
use warnings;

my $input_file;

if ($ARGV[0]) {
  $input_file = $ARGV[0];
}

else {
  die "File must be given as first arg\n";
}

open INPUT, "$input_file"
  or die "Couldn't open file: $!\n";

# Read each line of the file. If it's a line of text, we have
# to do some math, but otherwise we can just print the line.

while (<INPUT>) {
  my $line = $_;

  chomp $line;


  if ($line =~ /^<a name=\"[B]*\d?\.\d?\.(\d+)\">/
     || $line =~ /^<a name=\"(\d+)\">/) {
    # If the line we've read is a line of text, we need to
    # figure out if it's a 5th line. If it's not, we can just
    # print it, but if it is, we need to insert that line number.
    my $line_num = $1;

    if ($line_num % 5 == 0) {
      $line =~ s/<\/a><br>$/<span class=\"lineNum\">$line_num<\/span><\/a><br>/g;
      print "$line\n";
    }

    else {
      print "$line\n";
    }
  }

  else {
    # The line isn't special, so we can just print it
    # But not quite yet...
    print "$line\n";
  }
}