#34 Emulating GNU-Style Flags with Quota

The inconsistency between the command flags of various Unix systems is a perpetual problem and causes lots of grief for users who switch between any of the major releases, particularly between a commercial Unix (Solaris, HP-UX, and so on) and an open source Linux system. One command that demonstrates this problem is quota, which supports full-word flags on some Unix systems, while on others it accepts only one-letter flags.

A succinct shell script solves the problem, however, by mapping any full-word flags specified into the equivalent single-letter alternatives:

#!/bin/sh
# newquota - A front end to quota that works with full-word flags a la GNU.

# quota has three possible flags, -g, -v, and -q, but this script
#   allows them to be '--group', '--verbose', and '--quiet' too:

flags=""
realquota="/usr/bin/quota"

while [ $# -gt 0 ]
do
  case $1
  in
    --help          )  echo "Usage: $0 [--group --verbose --quiet -gvq]" >&2
                       exit 1 ;;
    --group | -group)  flags="$flags -g";       shift ;;
    --verbose | -verbose)  flags="$flags -v";   shift ;;
    --quiet | -quiet)  flags="$flags -q";       shift ;;
    --              )  shift;           break ;;
    *               )  break;          # done with 'while' loop!
  esac
done

exec $realquota $flags "$@"

How It Works

Did you notice that this script accepts both single- and double-dash prefixes for full words, making it actually a bit more flexible than the standard open source version, which insists on a single dash for one-letter flags and a double dash for full-word flags? With wrappers, the sky's the limit in terms of improved usability and increased consistency across commands.

Running the Script

There are a couple of ways to integrate a wrapper of this nature into your system. The most obvious is to rename the base quota command, rename this script quota, and then change the value of the realquota variable set at the beginning of the script. But you can also ensure that users have a PATH that looks in local directories before it looks in the standard Unix binary distro directories (e.g., /usr/local/bin before /bin and /usr/bin), which relies on the safe assumption that each user's PATH will see the script before it sees the real command. A third way is to add systemwide aliases so that a user typing quota actually invokes the newquota script.

The Results

$ newquota --verbose
Disk quotas for user dtint (uid 24810):
     Filesystem   usage   quota   limit   grace   files   quota   limit   grace
           /usr  338262  614400  675840           10703  120000  126000
$ newquota -quiet

The -q (quiet) mode emits output only if the user is over quota. You can see that this is working correctly from the last result because I'm not over quota.