Problem with Bash's command_not_found_handle()

Question

I get "command not found" error in Mac by the following command

md5sum *.java | uniq -d -w32

The reason is that Mac does not have -w option by default.

I would like to make Bash to do the following when the error occurs

1. put g at the beginning of the first command
2. put g at the beginning of a command which is after |

How can you make the error more useful?

[edit]

Problem: if Mac does not have the feature, I want use the features in coreutils. Therefore, the g in front of Mac's commands.

Answer 1

On Mac OS X works:

/sbin/md5 *.java | uniq -d

For gnu uniq see:

http://rudix.org/#coreutils

Answer 2

You cannot use command_not_found_handle() because the commands do exist; they just return an error ($? != 0) because of unrecognized parameters.

In these kinds of situations you should explicitly control the commands issued with a platform-specific prologue at the very beginning of the script, making the minimum number of assumptions about parameters, e.g.:

# defaults - satisfies most platforms
MD5SUM=md5sum
UNIQ=uniq
# per-platform exceptions
if [ "$OS" == "MacOS" ] ; then
  # use GNU variants by prefixing with g
  MD5SUM="g $MD5SUM"  # or use the native program, MD5SUM=md5
  UNIQ="g $UNIQ"      # or use the native program, UNIQ=uniq
elif [ "$OS" == "SomeOtherOS" ] ; then
  MD5SUM=md5hash # e.g. this platform computes MD5 sums with md5hash
fi
...
# optionally cross-check for GNU variants on all platforms
#  does uniq support -w32? (no error on dry run?) if so, use it!
$UNIQ -w32 /dev/null 2>/dev/null && UNIQ="$UNIQ -w32"
# optionally perform one last validation before proceeding
die() { echo "FATAL: $*" >&2 ; exit $1 ; }
$UNIQ /dev/null >/dev/null   || die $? "uniq is missing or failing: $UNIQ"
$MD5SUM /dev/null >/dev/null || die $? "md5sum is missing or failing: $MD5SUM"
...
$MD5SUM *.java | $UNIQ -d

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UPDATE

Note that it is also good practice, especially if your script will run as root, to not rely on $PATH -- you would want to specify the fully qualified locations for programs such as uniq or md5 or md5sum above, e.g. UNIQ=/bin/uniq, MD5SUM=/sbin/md5sum, etc.)

Cheers, V.

---

UPDATE2

To automatically prefix a bunch of commands with "g":

eval `for command in uniq md5sum grep sed ; do
  echo \`echo \$command | tr '[a-z]' '[A-Z]'\`=\"g \$command\"
done`