#!/usr/bin/perl -w
###############################################################################
=pod

=head1 NAME

join_lines - program for joining adjacent lines from stdin or one or more files

=head1 SYNOPSIS

B<join_lines> [options...] [text files...]

=head1 DESCRIPTION

B<join_lines> is used to join adjacent lines from stdin or one or more files,
trimming trailing line feeds and carriage returns, and sending the output to
stdout. Arguments are used to define the criteria and exact behavior.

=head1 OVERVIEW

B<join_lines> understands the following optional arguments:

=over 15

=item --help

Show this documentation.

=item --delimiter=<d>

B<join_lines> will use the specified delimiter <d> to separate joined lines. The
default is to use no delmiter when joining lines.

=item --lines=<n>

This will cause B<join_lines> to join every <n> lines into one line.

=item --record-separator=<s>

This will cause B<join_lines> to immediately start a new line when it encounters
a line solely containing <s>. That line itself will not otherwise be used. This
argument may be used in conjunction with --lines, but probably should not be. :)

=item --record-separator-empty-line

This works like --record-separator, but is a way to define an "empty" line as
being the record separator.

=back

=cut
###############################################################################

use strict;
use Pod::Usage;
use Getopt::Long;

my $help;
my $delimiter;
my $linecount;
my $record_separator;
my $record_separator_empty_line;

GetOptions(
	'delimiter=s' => \$delimiter,
	'lines=s' => \$linecount,
	'record-separator=s' => \$record_separator,
	'record-separator-empty-line' => \$record_separator_empty_line,
	'help|?' => \$help
);
pod2usage(-verbose => 2) if $help; 

my $count = 0;
my @lines = ();

sub join_lines {
    print join($delimiter || '', @lines) . "\n";
    @lines = ();
    $count = 0;
}

while (my $line = <>) {
    $count++;
    $line =~ s/[\r\n]+$//g;
    if (defined $record_separator_empty_line && $line eq '') {
        join_lines();
    } elsif (defined $record_separator && $line eq $record_separator) {
        join_lines();
    } elsif (defined $linecount && $count == $linecount) {
        push @lines, $line;
        join_lines();
    } elsif (! defined $linecount && ! defined $record_separator && ! defined $record_separator_empty_line) {
        print "$line\n"; # passthru when given no arguments
    } else {
        push @lines, $line;
    }
}
if (scalar(@lines) > 0) {
    print join($delimiter || '', @lines) . "\n";
}