How can I have no arguments mean help?

[kendalldita]

I hope this is the right way to ask questions. If not, please let me know.

How can I have a help message printed if no argument is supplied?

prog ( | -h | --help )

That didn't work, but It could be failing for some other reason.

[Sylvain303]

Hello @kendalldita,

The parser should be the same as docopt.

I'm not very active as you might have seen.

may be https://stackoverflow.com/questions/tagged/docopt ?

help is the default behavior:

./docopts -h 'usage: prog' :  -h
echo 'usage: prog'
exit 0

Did you look into examples subfolder?

[kendalldita]

Yes. None of them use the absence of any arguments, to mean help.

Aside from that, what would be the syntax to indicate that no argument means help.

[Sylvain303]

@kendalldita

Oh, you're right. This is a strange habit somewhat a bit rare, on unix at least. Because much command performs task when invoked, even without argument. Teaching people to ask specifically for help -h seems a better approach. So docopts, as docopt, won't help you to do so.

That said, you could use command keywords.

#!/usr/bin/env bash
#
# Launch nuclear missile, use with caution
#
# Usage: launch_missile.sh
#        launch_missile.sh go <where>
#
# Arguments:
#   <where>  coordinate x,y  same as open street map
#
#

# no PATH changes required if docopts binary is in the PATH already
PATH=..:$PATH
source ../docopts.sh
HELP=$(docopt_get_help_string $0)
version='0.1'

parsed=$(docopts -A args -h "$HELP" -V $version : "$@")
#echo "$parsed"                                                                                                                                                                               
eval "$parsed"

display_help()
{
    echo "$HELP"
}

launch_missile()
{
  echo "missile launched to coordinate: $1"
}

if [[ -z ${args[go]} || ${args[go]} != true ]]
then
    display_help
    exit 0
fi

launch_missile ${args[<where>]}

[kendalldita]

Thank you. That makes me wonder if it's clearer to just make no arguments act like -h, without including it in the help text.

[kendalldita]

I think this is resolved. I'm still interested any new ideas about it though.

[Sylvain303]

In fact, there's a simpler version:

#!/usr/bin/env bash
#
# Launch nuclear missile, use with caution
#
# Usage:  launch_missile.sh go <where>
#
# Arguments:
#   <where>  coordinate x,y  same as open street map
#

# no PATH changes required if docopts binary is in the PATH already
PATH=..:$PATH
source ../docopts.sh
HELP=$(docopt_get_help_string $0)
version='0.1'

parsed=$(docopts -A args -h "$HELP" -V $version : "$@")
#echo "$parsed"
eval "$parsed"

launch_missile()
{
  echo "missile launched to coordinate: $1"
}

launch_missile ${args[<where>]}

removing the no argument usage, give an error displaying the help short message with exit 64

As detailed in the documentation.