#!/bin/sh -u
#  $0 filename
#
#  Verify that the script has exactly one command line argument.  Verify
#  that the argument is a file, and that it is readable.  (Print an
#  error message and exit the script if these things are not true.)
#  Sort the file and display the first five lines.
#
# WARNING: Many of the comments in this file are "Instructor-Type"
#   comments and are *not* appropriate for real scripts.  Do not put
#   "Instructor-Type" comments into the scripts that you submit for marking.
#   I put them in my example files because I am teaching you how to
#   write scripts; do not submit my teaching comments back to me again.
#   Read the week7.txt notes for more details on good comment style.
#
# -IAN! idallen@ncf.ca

export PATH=/bin:/usr/bin
umask 022

# $# is the count of arguments
# -ne is a numeric comparison
# $* gives all the command line arguments as one single string.
# Error messages should always appear on standard error.
# Exit the script with a bad (non-zero) return code upon error.
#
if test $# -ne 1 ; then
	echo 1>&2 "Expecting one argument; found $# ($*)"
	exit 1
fi

# The "!" complements the exit code of the command: 0 to 1, 1 to 0.
# The complemeted exit code is tested by the "if" statement.
#
if ! test -f "$1" ; then
	echo 1>&2 "Argument '$1' is not a file"
	exit 1
fi

if ! test -r "$1" ; then
	echo 1>&2 "Argument '$1' is not readable"
	exit 1
fi

sort "$1" | head -5