$ program action flags options arguments
Program - the subject, single point of entry
Action - the predicate (verb), as simple and succinct as possible
Flags - booleans
Options - key/value pairs
Arguments - the direct object, target of the command
When displaying the command structure, use <> to highlight options, flags, and arguments.
Use  to display optional ones.
The whole string should only use lower case letters.
E.g. the only required argument in the following command is a single instance.
$ lxc delete [<remote>:]<instance>[/<snapshot>] [[<remote>:]<instance>[/<snapshot>]...] [flags]
Reads as the “predicate” in the command’s sentence (the verb of the sentence).
Specifies the ACTION within the PROGRAM to invoke.
Does one thing, and one thing well; simple and succinct.
Uses simple, common action verbs:
$ git clone
$ apt update
Aim to find the shortest, unique verb possible for the action that the command is performing.
One syllable is always better than two, which is always better than three. Three syllables are in general not acceptable to be used as an action.
Nested subcommands are to be used only in products where the CLI acts upon multiple objects, e.g. in MAAS you could take an action on a machine, a controller, a KVM host, etc. The commands acting on the primary object should not require the object to be mentioned.
$ maas commission <machine-name>
$ maas subnet reserve-range <IP-from> <IP-to>
If the program doesn’t require subcommands, consider adding another top level action, of verb-objectclass form:
$ juju add-unit
$ juju add-relation
Flags and OptionsHandled by the PROGRAM as booleans, either present or not, on the command line.
Must start with a single dash (-) or a double dash (–).
May have a single character representation.
- Single character flags must start with a single dash (-)
- Single character FLAGS can be stacked or combined
$ apt upgrade -yadf
$ apt upgrade -a -d -f -y
- Should have a descriptive representation for self-documenting scripts that must start with a double dash (–)
$ apt dist-upgrade -y
$ apt dist-upgrade --yes
- Must not be dependent on ordering
$ apt upgrade -a -d -f -y
$ apt upgrade -y -a -d -f
- Must at a minimum include these flags:
- KEY may have a single character representation
- KEY should have a double-dash descriptive representation
$ rsync -e “ssh -p 2222”
$ rsync --rsh=”ssh -p 2222”
- KEY and VALUE must support separation by whitespace
- KEY and VALUE may support separation by an equal sign
Handling Multiple values in a KEY (Tuple)
- When there are more than one values in a key
":"will be used to separate between the tuple values.
$ charmcraft release mycharm --revision=5 --channel=stable --resource foo:7 --resource bar:1
"," comma separation can be used to parse multiple values in a flag.
$ maas <profile> vmhose <id> compose pinned_cores= 1, 2, 3
$ juju deploy haproxy -n 2 --constraints spaces=dmz,^cms,^database
$ charmcraft release mycharm --revision=5 --channel=stable --resource foo:7, bar:1
ArgumentsThe “direct object” of the command’s sentence.
Must be the target of the PROGRAM and the ACTION.
Are any other terms which are neither FLAGS nor OPTIONS:
$ start apache2
$ docker pull ubuntu
$ git remote show
$ snapcraft list-revisions <snap-name>