#!/usr/bin/perl -w

# append_entries
# Appends entries from a source file to a destination file.  Only regular
# entries are copied; macro definitions, preambles, and comments are
# dropped.  User may supply a regex which the entry keys must match to be
# appended.
# Note that a "real" entry appender/database merger would be a lot more
# complicated than this!  Some things that would have to be handled:
#  * enforcing the structure of input entries (eg. making sure they
#    conform to the rules of some database structure such as 'Bib')
#  * doing any other checks particular to your database, such as ensuring
#    that journal or conference names come from an approved list of
#    "known" journals and conferences (to enforce consistent naming
#    across a large database)
#  * detecting and resolving key collisions
#  * adding any preambles in the source file to the destination file
#  * checking for duplicate macro definitions
#  * ensuring that macros used in the source file are defined in
#    the destination file
# by Greg Ward, 1998/04/04
# $Id$
# Copyright (c) 1997-2000 by Gregory P. Ward.  All rights reserved.  This file
# is part of the Text::BibTeX library.  This library is free software; you
# may redistribute it and/or modify it under the same terms as Perl itself.
use strict;
use Text::BibTeX;

my $usage = <<USAGE;
usage: $0 dest_file source_file [key_pattern]
       appends regular entries from <source_file> whose keys match
       <key_pattern> to <dest_file>; if <key_pattern> not supplied, all
       entries from <source_file> are taken

die $usage unless @ARGV == 2 || @ARGV == 3;
my ($dest_filename, $source_filename, $key_pattern) = @ARGV;

# Open the two files: dest_file in append mode (ultimately just using
# perl's builtin 'open'), and source_file in regular read-only mode.
my $dest_file = Text::BibTeX::File->new(">>$dest_filename")
   or die "couldn't open $dest_filename for appending: $!\n";
my $source_file = Text::BibTeX::File->new($source_filename)
   or die "couldn't open $source_filename: $!\n";

# Turn on 'value preservation' mode for the input file.  This is mainly so
# we don't lose the fact that macros are macros and numbers are numbers,
# but it also frees us from having to worry about predefined macros
# (such as the month names).
$source_file->preserve_values (1);

# And loop over all entries in the source file, optionally appending
# each one to the destination file.

while (my $entry = Text::BibTeX::Entry->new($source_file))
   # Skip this entry if it's not a regular entry -- that is, we just
   # drop '@string', '@comment', and '@preamble' entries, probably
   # unacceptable in the real world.
   next unless $entry->metatype == BTE_REGULAR;

   # Skip this entry if the user supplied a regex that keys must match
   # and this entry's key doesn't match.
   next if defined $key_pattern && $entry->key !~ /$key_pattern/o;

   # Otherwise, write this entry to the destination file.  Since $dest_file
   # was opened in append mode, $entry will be appended to the end of
   # $dest_file.
   $entry->write ($dest_file);
}  # while $source_file