xGroup()
{
USAGE="Usage:
$0 op1 [file ...]
$0 op2 [file ...]"

case "$1" in
op1)
	shift
	# do the work for op1
	;;
op2)
	shift
	# do the work for op2
	;;
*)
	echo "$USAGE" >&2
	exit 2
	;;
esac
}

#!/bin/sh
# x -- command that implements the ADT x

xGroup()
{
	#...
}

xGroup $*	

---------------------

$ x op1 file1 another-file

#!/bin/sh	
# the file unit.sh
include(unitGroup.sh)

include(echo-debug.sh)

unitGroup $*

# unit -- lecture unit extraction group
# SYNOPSIS:  this group of operations
#  understands the Outline-files.txt file
#  found in each lecture unit directory.

include(echo-debug.sh)

include(noteGroup.sh)

unitGroup()
{
USAGE="Usage: 
$0 files [directory ...]
$0 examples [directory ...]
$0 handouts [directory ...]
$0 outline [directory ...]
$0 print [directory ...]"

# ...

mainunitfiles()
{
	# ...
}

allunitfiles()
{
	# ...
}

case "$1" in
files)
  shift
  allunitfiles $* || exit 1
  ;;
examples)
  shift
  noteGroup examples `mainunitfiles $*`
  ;;
handouts)
  shift
  noteGroup handouts `mainunitfiles $*`  
  ;;
outline)
  shift
  # Extract the outline used in a unit
  noteGroup outline `mainunitfiles $*`
  ;;
print)
  shift
  print ascii `allunitfiles $*`
  ;;
*)
  echo "$USAGE" >&2
  exit 2
  ;;
esac
}