user-tools/maskfiles

   1 #!/usr/bin/env perl
   2
   3 =pod
   4
   5 =head1 NAME
   6
   7 maskfiles - Lay over several text files on top of each other like transparency sheets for overhead projectors
   8
   9 =head1 SYNOPSIS
  10
  11 maskfiles [I<OPTIONS>] [--] I<FILE_1> I<FILE_2> [I<FILE_3> ... I<< FILE_B<n> >>]
  12
  13 =head1 DESCRIPTION
  14
  15 Take files from 1 to B<n> and virtually put them on top of each other
  16 by matching byte offsets.
  17 If a file from the upper layer have a hole (space by default, otherwise see --hole-char option),
  18 then the char on lower layers "looks through" it.
  19 Non hole chars just block the lower layers, so they are visible at the end.
  20
  21 Output is STDOUT.
  22 No input files are written.
  23
  24 =head1 OPTIONS
  25
  26 =over 4
  27
  28 =item -h, --hole-chars I<CHARS>
  29
  30 Which chars are to be looked through.
  31 By default space is the only hole char.
  32 Add underscore to it by example: --hole-chars=" _"
  33
  34 =item --nul-hole
  35
  36 Make NUL chars to look through as well.
  37
  38 =item --linewise
  39
  40 Respect line breaks.
  41
  42 =back
  43
  44 =cut
  45
  46
  47 use Fcntl qw/:flock :seek/;
  48 use Getopt::Long qw/:config no_ignore_case no_bundling no_getopt_compat no_auto_abbrev require_order/;
  49 use Pod::Usage;
  50 use POSIX;
  51 no if ($] >= 5.018), 'warnings' => 'experimental::smartmatch';
  52
  53
  54 $OptHoleChars = " ";
  55 $OptHoleNUL = 0;
  56 $OptLinewise = 0;
  57
  58 GetOptions(
  59         'h|hole|holechar|hole-char|holechars|hole-chars=s' => \$OptHoleChars,
  60         'nul-hole' => \$OptHoleNUL,
  61         'l|linewise!' => \$OptLinewise,
  62         'help' => sub { pod2usage(-exitval=>0, -verbose=>99); },
  63 ) or pod2usage(-exitval=>2, -verbose=>99);
  64
  65
  66 $OptHoleChars .= chr(0) if $OptHoleNUL;
  67
  68 @overlay_files = @ARGV;
  69 @layers = ();
  70
  71 for my $path (reverse @overlay_files)
  72 {
  73         open my $fh, '<', $path or die "$0: open: $path: $!\n";
  74         push @layers, {'fh'=>$fh, 'eol'=>0};
  75 }
  76
  77 while(1)
  78 {
  79         my $char0;
  80         my $char;
  81
  82         last if not grep {defined $_->{'fh'}} @layers;
  83
  84         if($OptLinewise and not grep {defined $_->{'fh'} and not $_->{'eol'}} @layers)
  85         {
  86                 # all files are at EOL, reset flags
  87                 map {$_->{'eol'} = 0} @layers;
  88         }
  89
  90         for my $layer (@layers)
  91         {
  92                 my $fh = $layer->{'fh'};
  93                 next if not defined $fh;
  94                 next if $OptLinewise and $layer->{'eol'};
  95
  96                 my $nbytes = read $fh, $char, 1;
  97                 if($nbytes != 1)
  98                 {
  99                         $layer->{'fh'} = undef;
 100                         next;
 101                 }
 102                 if($OptLinewise and $char eq "\n")
 103                 {
 104                         $layer->{'eol'} = 1;
 105                         next;
 106                 }
 107
 108                 if(not defined $char0 and $OptHoleChars !~ /\Q$char\E/)
 109                 {
 110                         $char0 = $char;
 111                 }
 112         }
 113
 114         $char0 = $char if not defined $char0;  # there are holes all the way down to the lowermost layer
 115         print $char0;
 116 }