#!/bin/sh -u
# look for an optional string in the Unix password file
#------------------------------------------------------------
# Syntax:  $0 [ string ]
#------------------------------------------------------------
# Purpose:
#  Take one optional argument and look for it in the password file.  If the
#  argument is missing, prompt for it and read it.  Exit non-zero if there
#  are not 0 or 1 arguments or if the string is empty.
#------------------------------------------------------------
# Student Name:                  Ian! D. Allen
# Algonquin EMail Address:       alleni
# Student Number:                000-000-000
# Course Number:                 DAT2330
# Lab Section Number:            010
# Professor Name:                Ian! D. Allen
# Assignment Name/Number/Date:   Sample Assignment Label
# Comment:                       This is a sample assignment label.
#      see http://teaching.idallen.com/assignment_standards.html
#-------------------------------------------------------------

# Set a standard shell search path and a friendly umask.
#
PATH=/bin:/usr/bin ; export PATH
umask 022

#echo "DEBUG the count of arguments is $#"

# Make sure we have 0 or 1 arguments; exit non-zero if more than 1.
#
if test "$#" -gt 1 ; then
	echo 1>&2 "$0: Number of arguments $# is greater than 1: ($*)"
	exit 1
fi

# Prompt on stderr and read string from standard input if no argument.
# If a command line argument is present, use it as the string.
#
if test $# -eq 0 ; then
	echo 1>&2 "Enter a string to search for:"
	read string
else
	string="$1"
fi

#echo "DEBUG the string is $string"

# Make sure string is not empty; exit non-zero if it is empty.
#
if test "$string" = "" ; then
	echo 1>&2 "$0: empty string not accepted - nothing done"
	exit 2
fi

# Look for the string in the Unix password file.
#
grep "$string" /etc/passwd

# Scripts exit with the return code of the last command executed.