OpenStack or Bust, Part 9: stack_id script

#!/bin/bash
#set -x
######################################################################
###
### stack_id
### --------
###
### Given name of tenant, user, role, etc, printout keystone id
###
######################################################################

source /root/.keystonerc

function USAGE {
    cat <<-EOF
        USAGE:
          $(basename $0) <option> <data_name>

        OPTIONS:
          -t    tenant
          -u    user
          -r    role
          -s    service
          -i    image
          -n    network
          -b    subnet
          -o    router

        ARGS:
          data_name    name of tenant, user, or role whose id you want

        EXAMPLE:
          $(basename $0) -u admin
EOF
}

query="/usr/bin/keystone"

### Get Options
### Select data table to query
while getopts ":htursinbo" opt; do   # Leading colon xlates unknown opts to ?
    # Pick the first option seen, ignore rest
    if [[ -n "$table" ]] ; then
        continue
    fi
    case $opt in
        h) USAGE; exit 1;;
        t) table=tenant;;
        u) table=user;;
        r) table=role;;
        s) table=service;;
        i) table=image; query="/usr/bin/glance";;
        n) table=net; query="/usr/bin/quantum";;
        b) table=subnet; query="/usr/bin/quantum";;
        o) table=router; query="/usr/bin/quantum";;
        ?) printf "[ERROR] Invalid option\n\n" >&2
           USAGE
           exit 1;;
    esac
done
shift $((OPTIND - 1))

### Get data name
name=$1

### Early Exit
table_regex="^(tenant|user|role|service|image|net|subnet|router)$"
if [[ -z "$name" || -z "$table" || ! $table =~ $table_regex ]] ; then
    printf "[ERROR] Bad usage\n\n"
    USAGE
    exit 1
fi

### Run query
out=$( ${query} ${table}-list 2>/dev/null |
    awk -v name=$name '$4 == name {print $2}' )

### Did we get an answer?
if [[ -z "$out" ]] ; then
    echo "No such $table $name" >&2
    exit 1
else
    echo $out
fi