CODEWITHSUNDEEP
bashexit-code
Eero Aaltonen
Eero Aaltonen

Reputation: 4425

Exit Code when called with No Arguments

I have a script that requires at least one argument. If the arguments are incorrect I will obviously return a non-zero exit code.

I have decided to print the usage instructions when called with no arguments, but I'm uncertain of the exit code. Should it be

An argument could be made either way. Is some option recommended?

Upvotes: 4

Views: 4024

Answers (3)

Eero Aaltonen
Eero Aaltonen

Reputation: 4425

This is what I decided on using, based mostly on Inians answer and the reserved exit codes presented here.

I decided on somewhat reusing the exit codes defined in /usr/include/asm-generic/errno-base.h1. There was nothing suitable for "too little arguments", so I picked the first one from the 64-113 range.

# Error codes
E2BIG=7
EINVAL=22
E2SMALL=64

NAME="my-script"
USAGE=$(cat << END
    the help text
RETURN CODES
    $NAME has the following return codes:

    0   success
    $E2BIG  Argument list too long
    $EINVAL Invalid argument
    $E2SMALL    Argument list too short
END
)

# This script requires exactly one argument. If less are provided it prints
# the USAGE instructions
if [ ${#} -lt 1 ] ; then
    printf '%s\n' "${USAGE}"
    exit $E2SMALL
fi
if [ "${1}" = "-h" ] || [ "${1}" = "--help" ] ; then
    printf '%s\n' "${USAGE}"
    exit 0
fi
if [ ${#} -gt 1 ] ; then
    printf '%s\n' "${USAGE}"
    exit $E2BIG
fi

It's a bit verbose, but at least there's a properly defined error code if the script is called improperly.

1 This may be debatable, but since the codes were already defined...

Upvotes: 1

paxdiablo
paxdiablo

Reputation: 881283

It depends on whether you want the callers of your script to know programatically why it failed.

If, for example, it will only ever be run by a human, you could just return 1 and rely on the error text to inform them.

You could even return zero regardless if you only ever want a human to easily know (via the output) if it failed but I would consider this very bad form - Microsoft have made this mistake in the past with some of their commands not setting %errorlevel%, making it very difficult for a script to figure out whether it's worked or not.

Even if you decide not to indicate why it failed, you should at least indicate that it failed.

If you want a program to easily figure out why it failed, return a different code for each discernible error type.

Upvotes: 4

Inian
Inian

Reputation: 85560

Any Unix command when it returns control to its parent process returns a code, number between 0 and 255.

Success is traditionally represented with exit 0; failure is normally indicated with a non-zero exit-code. This value can indicate different reasons for failure.

So what you have also is another case of unsuccessful completion of your program which should be treated as returning a proper error code and not 0.

Also note that traditional Unix system calls don't signal an error code for empty arguments, they have to be caught explicitly. There are ones for argument list too long (E2BIG) and invalid arguments (EINVAL).

Upvotes: 2

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