#! /usr/bin/perl

# ----------------------------------------------------------------
sub usage()
{
	print "\n";
	print "Usage: $0 [column delimiters] {column numbers ...} {file names ...}\n";
	print "  There must be at least one column number.  Columns are numbered one-up.\n";
	print "  There may be zero file names, in which case input is taken from stdin.\n";
	print "\n";
	print "Column delimiters for input and output:\n";
	print "  -t:  Column delimiter is one tab.\n";
	print "  -s:  Column delimiter is one or more whitespace characters (default).\n";
	print "  -c:  Column delimiter is one comma.\n";
	print "  -n:  Column delimiter is the empty string, e.g. each character is a column.\n";
	print "\n";
	print "Column delimiter for input:  -it, -is, -ic, -in\n";
	print "Column delimiter for output: -ot, -os, -oc, -on\n";
	print "\n";
	exit(1);
}

# ----------------------------------------------------------------
# Defaults:
my $delimpat = "\s+";
my $delimout = " ";

# There are three types of arguments:
# 1. Zero or more column-delimiter specifications, which begin with
#    slash or dash.
# 2. One or more column numbers, which are decimal numbers.
# 3. Zero or more file names, which are whatever is left.

# First, scan the command line (@ARGV) for column-delimiter specifications,
# removing them from @ARGV.
while (@ARGV && ($ARGV[0] =~ m:^[-/]:)) {
	my $opt = $ARGV[0];
	$opt =~ s/^.//;

	if ($opt eq "h") {
		usage();
	}
	elsif ($opt eq "?") {
		usage();
	}

	elsif ($opt eq "t") {
		$delimpat = "\t";
		$delimout = "\t";
	}
	elsif ($opt eq "c") {
		$delimpat = ",";
		$delimout = ",";
	}
	elsif ($opt eq "s") {
		$delimpat = "\s+";
		$delimout = " ";
	}
	elsif ($opt eq "n") {
		$delimpat = "";
		$delimout = "";
	}

	elsif ($opt eq "it") {
		$delimpat = "\t";
	}
	elsif ($opt eq "ic") {
		$delimpat = ",";
	}
	elsif ($opt eq "is") {
		$delimpat = "\s+";
	}
	elsif ($opt eq "in") {
		$delimpat = "";
	}

	elsif ($opt eq "ot") {
		$delimout = "\t";
	}
	elsif ($opt eq "oc") {
		$delimout = ",";
	}
	elsif ($opt eq "os") {
		$delimout = " ";
	}
	elsif ($opt eq "n") {
		$delimout = "";
	}

	else {
		print "Unrecognized option \"$ARGV[0]\".\n";
		usage();
	}
	shift @ARGV;
}

# Second, scan the command line (@ARGV) for column numbers (decimal numbers),
# removing them from @ARGV.

my @colnos = ();
my $colnocount = 0;

while (1) {
	my $arg = $ARGV[0];
	if ($arg =~ m/^[0-9]+$/) {
		my $colno = shift @ARGV;
		die "$0: column numbers must be positive" if ($colno <= 0);
		push @colnos, $colno;
		$colnocount++;
	}
	else {
		last;
	}
}

# There must be at least one column number.
unless ($colnocount > 0) {
	usage();
}

# Third, whatever is left on the command line is assumed to be a file name.

my $lineno = 0;
while ($line = <>) {
	$lineno++;

	chomp $line;
	$line =~ s/^\s+//;
	my @fields;
	if ($delimpat eq "\s+") {
		@fields = split /\s+/, $line;
	}
	else {
		@fields = split /$delimpat/o, $line;
	}
	my $first_column = 1;

	for my $colno (@colnos) {
		if ($first_column == 1) {
			$first_column = 0;
		}
		else {
			print $delimout;
		}
		#if ($colno >= @fields) {
			#die "\nInsufficient number of columns in input at line $lineno.\n";
			#print "\nInsufficient number of columns in input at line $lineno.\n";
		#}
		#else {
			print $fields[$colno-1];
		#}
	}
	print "\n";
}