Listing 4: getnum

##################################################
#
#  getnum
#
#  usage: getnum <min> <max> "<prompt>"
#
#       obtain an integer from the user, and return it on standard
#  output.  Allow the user to abort by pressing return.
#  Intended for use in shell scripts in conjunction with
#  backquote substitution, as in:
#
#  pick=`getnum 1 10 "Pick a number from 1 to 10"`
#

min=$1
max=$2
prompt=$3

while true
do
echo "$prompt [<return> to abort] > \c" >&2      # *see note 1
read n
[ "$n" = "" ] && echo "ABORT" && exit
if echo $1 $n $2 | awk '{ if (($1<=$2) && ($2<=$3)) exit 0 ;
else exit 1
}'                   # *see note 2
then
echo $n      # return the number on stdout
exit
fi
done

#################################
#
#  Notes:
#
#  1)  The prompt is echoed to stderr rather than stdout, so that only the
#  chosen number is returned on stdout.
#
#  2)  Piping the number to awk is a simple way to make sure we have numbers
#  since awk handles this for us.  Note that if O is valid in the range of
#  numbers (min to max), then a letter will count as zero.
#