#!/bin/sh -u
#
#     $0  [filename]
#
# A script that chooses cases based on the number of characters
# in the file that is the optional command line argument.
# If no file name is given, we prompt for one.
#
# 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  June 2001

# All scripts must start with lines similar to these two:
#
export PATH=/bin:/usr/bin
umask 022

# The first thing all programs must do is validate their arguments.
#
# We do different things depending on the number of arguments given.
#   0 args -> prompt for a file name.
#   1 arg  -> use the given file name.
#  >1 arg  -> error.
# The tr removes the newline normally added by "echo".
# Prompts must always appear on stderr, not on stdout.
# We output the "extra" arguments in case of error, so that the
# user knows what s/he typed by mistake.
#
case "$#" in
0)	echo "Enter a file name: " | tr -d '\n' 1>&2
	read filename
	;;
1)	filename="$1"
	;;
*)	echo 1>&2 "$0: Expecting 0 or 1 file name; found $# ($*)"
	exit 1
	;;
esac

# Real-world scripts probably would not do this echo:
#
echo "Processing file '$filename'."

# Continue to validate the input.  Validating input can take
# up most of a script!
#
if [ ! -f "$filename" ]; then
	echo 1>&2 "$0: Argument '$filename' is not an existing file."
	exit 1
	
fi

if [ ! -r "$filename" ]; then
	echo 1>&2 "$0: File '$filename' is not readable."
	exit 1
	
fi

# The tr deletes the blanks around the number output by wc.
# Redirecting input to wc avoids wc outputting the file name
# (because there is no file name - wc is counting stdin).
# The DEBUG line lets us know that the wc line worked;
# remove it (comment it out) when the script is working.
#
nchars=$(wc -c <"$filename" | tr -d ' ') || exit $?
echo "DEBUG The file contains $nchars characters."

# Choose cases based on number of chars counted in the file.
# Remember!  First match wins - only one of these cases will execute.
#
case "$nchars" in
0)
	echo "The file is empty."
	;;
[0-9])
	echo "The file contains 1-9 characters."
	;;
[0-9][0-9])
	echo "The file contains 10-99 characters."
	;;
[0-9][0-9][0-9] | [0-9][0-9][0-9][0-9])
	echo "The file contains 100-9999 characters."
	;;
*)	echo "The file contains $nchars and that means it is big!"
	;;
esac

exit 0