#!/bin/sh -u
# Demonstrate method 2 for prompting for missing command line arguments.
#------------------------------------------------------------------
# Syntax:
#  $0 [ permissions [ pathname ] ]
#------------------------------------------------------------------
# Purpose:
#  Apply the permissions to the pathname, only if the pathname is
#  writable by the script user.  Prompt for missing command arguments.
#
#  Comments in this script show the Input/Validation/Processing
#  phases of the script.
#------------------------------------------------------------------
# -IAN! idallen@idallen.ca

# Set the search path for the shell to be the standard places.
# Set the umask to be non-restrictive and friendly to others.
#
PATH=/bin:/usr/bin ; export PATH
umask 022

#-------------------------------------------------------------
# Input section.

# Exit the script if more than two arguments are supplied.
#
if [ $# -gt 2 ]; then
    echo 1>&2 "$0: Expecting permissions and pathname; found $# args ($*)"
    exit 1
fi

# The user might enter 0, 1, or 2 arguments.
# Handle all the cases using a series of IF/ELSE tests.
# This version reads permissions and then pathname if both are missing.
#
if [ $# -lt 1 ]; then
    echo 1>&2 "Enter permissions:"
    read permissions || exit $?
else
    permissions="$1" # first arg is permissions
fi
if [ $# -lt 2 ]; then
    echo 1>&2 "Enter pathname:"
    read pathname || exit $?
else
    pathname="$2"    # second arg is pathname
fi
#
#-------------------------------------------------------------

#-------------------------------------------------------------
# Argument validation section.
#
# Exit if either string is empty (nothing entered).
# Exit if the pathame does not exist or is not writable.
#
if [ -z "$permissions" -o -z "$pathname" ] ; then
    echo 1>&2 "$0: empty permissions or pathname; nothing done"
    exit 2
fi
if [ ! -e "$pathname" ] ; then
    echo 1>&2 "$0: pathname '$pathname' does not exist; nothing done"
    exit 3
fi
if [ ! -w "$pathname" ] ; then
    echo 1>&2 "$0: pathname '$pathname' is not writable; nothing done"
    exit 4
fi
#
#-------------------------------------------------------------

#-------------------------------------------------------------
# Processing section.
# We have validated the arguments before doing any processing.
#
if chmod "$permissions" "$pathname" ; then
    echo "Permissions changed to '$permissions' on '$pathname'"
else
    echo 1>&2 "$0: chmod '$permissions' '$pathname' failed with status $?"
    exit 5
fi