=head1 Documentation for sort.pl

 20001205 - Program originally written by Chad Kulesa
 20001205 - Program modified and documented by Larry Boatman

 Purpose:  Passed up to four parameters, the first two of which (input and output file 
		names) are required (sort key offset from beginning of record and length of 
		sort key are optional), this "generic" sort program reads in the input file 
		(name passed in the first parameter), performs the sort (see further 
		documentation below) , and writes out the output file (name passed as second 
		parameter).

=cut

=pod

 Declare an "assignable" array as the "output" array

=cut

my @lines2;

=pod

 if less than or more than the number of arguments then 
	display a "usage" message
	exit program

 Open the input file or report why not and exit
 Read entire file into an "input" array
 Close the input file
 
 Sort the "input" array into the "output" array based on the comparison of sort keys 
 built depending upon the number of arguments passed to the program as follows:

	if no sort key offset and no sort key length is passed, then 
		sort on entire record
	else 
		if a sort key offset is passed but no sort key length, then 
			sort on entire record beginning from the sort key offset
		else
			if both a sort key offset and sort key length is passed, then 
				sort on key beginning at sort key offset for sort key length 
			end if
		end if
	end if
 
 Open the output file
 Write the sorted "output" array to the output file
 Close the output file

=cut

if (($#ARGV < 1) || ($#ARGV > 3)) {
	print "usage: $0 input.filename output.filename [sort key offset] [sort key length]\n\n";
	exit;
}

open (INPUT,"$ARGV[0]") || die "Cannot open $ARGV[0] for reading:  $!";
my @lines = <INPUT>;
close INPUT;

if ($#ARGV == 1){
	@lines2 = sort {$a cmp $b} @lines;
} elsif ($#ARGV == 2){
	@lines2 = sort {substr($a, $ARGV[2]) cmp substr($b, $ARGV[2])} @lines;
} elsif ($#ARGV == 3){
	@lines2 = sort {substr($a, $ARGV[2], $ARGV[3]) cmp substr($b, $ARGV[2], $ARGV[3])} @lines;
}

open (OUTPUT,">$ARGV[1]") || die "Cannot open $ARGV[1] for writing:  $!";
print OUTPUT @lines2;
close OUTPUT;