🚀 go-pugleaf

Is there an elegant way to have a 'gawk' script act like a Unix filter yet
have a 'help' paragraph automatically written when the script is improperly
used?  Specifically, how do I get it to behave as a filter at the end of a
pipe?  Here's some code that I've been dinging with.  The script name
is gawker.  Thanks for any help!
------------------------------------------------------------------------------
#!/usr/bin/gawk -f
BEGIN	{
	if (ARGC == 1) {
		print "Usage: gawker file.in > file.out\n"
		print "       Filter data\n"
		print "Input:   file.in   <STDIN>"
		print "Output:  file.out  <STDOUT>"
		exit
	}
	print "begin action"
}
	{
	print		# echo standard input to standard output
}
END	{
	if (ARGC == 1) exit
	print "end action"

--------------------------------------------------------------------------
$ gawker
Usage: gawker file.in > file.out

       Filter data

Input:   file.in   <STDIN>
Output:  file.out  <STDOUT>
$ gawker file.in > file.out		# behaves OK
$ cat file.in | gawker > file.out	# bombs

-- 
JoAnne Bassett                          Aromatherapy grade essential oils,
Certified Aromatherapist       >><<     blends, diffusers, floral waters,
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(206) 451-0845                 >><<     blending oils, books, etc.