#!/usr/bin/perl
use strict;  use warnings;


sub help {
  my $cmdname = $0;
  $cmdname =~ s:.*/::;
  print "$cmdname - list the BibTeX keys defined in bib files.\n";
  print "Input is read from stdin or from named files.\n";
  print "The keys are sorted lexicographically, with each key listed once even if\n";
  print "it is defined more than once.\n";
  print "If a key is defined more than once, a message is printed to STDERR.\n";
  print "  -help  Show this help.\n";
}

my $arg;
my $numFiles = 0;
my $sep = "\n";
my $v = "";
my $k = "";
my %keysDefined = ();
my $count = 0;
foreach $arg (@ARGV) {
  if ($arg =~ /^-/) {
    if    ($arg =~ /^-+help$/) {
      &help;
      exit 0;
    }
    else {
      print "Unexpected argument \"$arg\".\n";
      exit 0;
    }
  }
  else {
    if (open(HIN, $arg)) {
      &bibFile(\*HIN, $arg);
      close HIN;
      ++$numFiles;
    }
    else {
      print STDERR "Can't open input file \"$arg\".\n";
      exit -1;
    }
  }
}
if (0 == $numFiles) {
  &bibFile(\*STDIN, "<stdin>");
}
if (scalar %keysDefined) {
  foreach $k (sort keysDefined %keysDefined) {
    if ($count++) {
      print "$sep";
    }
    print "$k";
  }
  print "\n";
}

sub bibFile {
  my $IN = $_[0];
  my $fname = $_[1];
  my $lineno = 0;
  while (<$IN>) {
    ++$lineno;
    chomp;
    if (/^@[a-zA-Z]+[({]([-0-9a-zA-Z+]+),$/) {
       s/^@[a-zA-Z]+[({]([-0-9a-zA-Z+]+),$/$1/;
      #print "$_\n";
      my $key = $_;
      if (defined $keysDefined{$key}) {
        print STDERR "($fname:$lineno)  '$key' multiply defined ($keysDefined{$key}).\n";
      }
      $keysDefined{$_} = "$fname:$lineno";
    }
  }
}