Commander.js
The complete solution for node.js command-line interfaces, inspired by Ruby's commander.
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- Commander.js
Installation
npm install commander
Declaring program variable
Commander exports a global object which is convenient for quick programs. This is used in the examples in this README for brevity.
const program = ;programversion'0.0.1';
For larger programs which may use commander in multiple ways, including unit testing, it is better to create a local Command object to use.
const Command = ;const program = ;programversion'0.0.1';
Options
Options are defined with the .option()
method, also serving as documentation for the options. Each option can have a short flag (single character) and a long name, separated by a comma or space or vertical bar ('|').
The options can be accessed as properties on the Command object. Multi-word options such as "--template-engine" are camel-cased, becoming program.templateEngine
etc. See also optional new behaviour to avoid name clashes.
Multiple short flags may optionally be combined in a single argument following the dash: boolean flags, the last flag may take a value, and the value.
For example -a -b -p 80
may be written as -ab -p80
or even -abp80
.
You can use --
to indicate the end of the options, and any remaining arguments will be used without being interpreted.
This is particularly useful for passing options through to another
command, like: do -- git --version
.
Options on the command line are not positional, and can be specified before or after other command arguments.
Common option types, boolean and value
The two most used option types are a boolean flag, and an option which takes a value (declared using angle brackets). Both are undefined
unless specified on command line.
const program = ; program ; program; if programdebug console;console;if programsmall console;if programpizzaType console;
$ pizza-options -d
program.parse(arguments)
processes the arguments, leaving any args not consumed by the program options in the program.args
array.
Default option value
You can specify a default value for an option which takes a value.
const program = ; program ; program; console;
$ pizza-optionscheese: blue$ pizza-options --cheese stiltoncheese: stilton
Other option types, negatable boolean and flag|value
You can specify a boolean option long name with a leading no-
to set the option value to false when used.
Defined alone this also makes the option true by default.
If you define --foo
first, adding --no-foo
does not change the default value from what it would
otherwise be. You can specify a default boolean value for a boolean flag and it can be overridden on command line.
const program = ; program ; const sauceStr = programsauce ? 'sauce' : 'no sauce';const cheeseStr = programcheese === false ? 'no cheese' : ` cheese`;console;
$ pizza-optionsYou ordered a pizza with sauce and mozzarella cheese$ pizza-options --sauceerror: unknown option '--sauce'$ pizza-options --cheese=blueYou ordered a pizza with sauce and blue cheese$ pizza-options --no-sauce --no-cheeseYou ordered a pizza with no sauce and no cheese
You can specify an option which functions as a flag but may also take a value (declared using square brackets).
const program = ; program ; program; if programcheese === undefined console;else if programcheese === true console;else console;
$ pizza-optionsno cheese$ pizza-options --cheeseadd cheese$ pizza-options --cheese mozzarellaadd cheese type mozzarella
Custom option processing
You may specify a function to do custom processing of option values. The callback function receives two parameters, the user specified value and the previous value for the option. It returns the new value for the option.
This allows you to coerce the option value to the desired type, or accumulate values, or do entirely custom processing.
You can optionally specify the default/starting value for the option after the function.
const program = ; { // parseInt takes a string and an optional radix return ;} { return previous + 1;} { return previous;} { return value;} program ; program; if programfloat !== undefined console;if programinteger !== undefined console;if programverbose > 0 console;if programcollectlength > 0 console;if programlist !== undefined console;
$ custom -f 1e2float: 100$ custom --integer 2integer: 2$ custom -v -v -vverbose: 3$ custom -c a -c b -c c[ 'a', 'b', 'c' ]$ custom --list x,y,z[ 'x', 'y', 'z' ]
Required option
You may specify a required (mandatory) option using .requiredOption
. The option must have a value after parsing, usually specified on the command line, or perhaps from a default value (say from environment). The method is otherwise the same as .option
in format, taking flags and description, and optional default value or custom processing.
const program = ; program ; program;
$ pizzaerror: required option '-c, --cheese <type>' not specified
Version option
The optional version
method adds handling for displaying the command version. The default option flags are -V
and --version
, and when present the command prints the version number and exits.
programversion'0.0.1';
$ ./examples/pizza -V0.0.1
You may change the flags and description by passing additional parameters to the version
method, using
the same syntax for flags as the option
method. The version flags can be named anything, but a long name is required.
programversion'0.0.1' '-v, --vers' 'output the current version';
Commands
You can specify (sub)commands for your top-level command using .command()
or .addCommand()
. There are two ways these can be implemented: using an action handler attached to the command, or as a stand-alone executable file (described in more detail later). The subcommands may be nested (example).
In the first parameter to .command()
you specify the command name and any command arguments. The arguments may be <required>
or [optional]
, and the last argument may also be variadic...
.
You can use .addCommand()
to add an already configured subcommand to the program.
For example:
// Command implemented using action handler (description is supplied separately to `.command`)// Returns new command for configuring.program description'clone a repository into a newly created directory' action { console; }; // Command implemented using stand-alone executable file (description is second parameter to `.command`)// Returns top-level command for adding more commands.program ; // Command prepared separately.// Returns top-level command for adding more commands.program ;
Configuration options can be passed with the call to .command()
. Specifying true
for opts.noHelp
will remove the command from the generated help output. Specifying true
for opts.isDefault
will run the subcommand if no other subcommand is specified (example).
Specify the argument syntax
You use .arguments
to specify the arguments for the top-level command, and for subcommands they are included in the .command
call. Angled brackets (e.g. <required>
) indicate required input. Square brackets (e.g. [optional]
) indicate optional input.
const program = ; program version'0.1.0' arguments'<cmd> [env]' action { cmdValue = cmd; envValue = env; }; program; if typeof cmdValue === 'undefined' console; process;console;console;
The last argument of a command can be variadic, and only the last argument. To make an argument variadic you
append ...
to the argument name. For example:
const program = ; program version'0.1.0' action { console; if otherDirs otherDirs; }; program;
The variadic argument is passed to the action handler as an array.
Action handler (sub)commands
You can add options to a command that uses an action handler. The action handler gets passed a parameter for each argument you declared, and one additional argument which is the command object itself. This command argument has the values for the command-specific options added as properties.
const program = ; program action { console } program
You may supply an async
action handler, in which case you call .parseAsync
rather than .parse
.
{ /* code goes here */ } { program actionrun; await program;}
A command's options on the command line are validated when the command is used. Any unknown options will be reported as an error.
Stand-alone executable (sub)commands
When .command()
is invoked with a description argument, this tells Commander that you're going to use stand-alone executables for subcommands.
Commander will search the executables in the directory of the entry script (like ./examples/pm
) with the name program-subcommand
, like pm-install
, pm-search
.
You can specify a custom name with the executableFile
configuration option.
You handle the options for an executable (sub)command in the executable, and don't declare them at the top-level.
// file: ./examples/pmconst program = ; program version'0.1.0' ;
If the program is designed to be installed globally, make sure the executables have proper modes, like 755
.
Automated help
The help information is auto-generated based on the information commander already knows about your program. The default
help option is -h,--help
. (example)
$ node ./examples/pizza --helpUsage: pizza [options] An application
A help
command is added by default if your command has subcommands. It can be used alone, or with a subcommand name to show
further help for the subcommand. These are effectively the same if the shell
program has implicit help:
shell helpshell --help shell help spawnshell spawn --help
Custom help
You can display extra information by listening for "--help". (example)
program ; // must be before .parse()program;
Yields the following help output:
Usage: custom-help [options] Options: -f, --foo enable some foo -h, --help display help for command Example call: $ custom-help --help
.usage and .name
These allow you to customise the usage description in the first line of the help. The name is otherwise deduced from the (full) program arguments. Given:
program name"my-command"
The help will start with:
Usage: my-command [global options] command
.help(cb)
Output help information and exit immediately. Optional callback cb allows post-processing of help text before it is displayed.
.outputHelp(cb)
Output help information without exiting. Optional callback cb allows post-processing of help text before it is displayed.
.helpInformation()
Get the command help information as a string for processing or displaying yourself. (The text does not include the custom help
from --help
listeners.)
.helpOption(flags, description)
Override the default help flags and description.
program ;
.addHelpCommand()
You can explicitly turn on or off the implicit help command with .addHelpCommand()
and .addHelpCommand(false)
.
You can both turn on and customise the help command by supplying the name and description:
program;
Custom event listeners
You can execute custom actions by listening to command and option events.
program; program;
Bits and pieces
.parse() and .parseAsync()
The first argument to .parse
is the array of strings to parse. You may omit the parameter to implicitly use process.argv
.
If the arguments follow different conventions than node you can pass a from
option in the second parameter:
- 'node': default,
argv[0]
is the application andargv[1]
is the script being run, with user parameters after that - 'electron':
argv[1]
varies depending on whether the electron application is packaged - 'user': all of the arguments from the user
For example:
program; // Explicit, node conventionsprogram; // Implicit, and auto-detect electronprogram;
Avoiding option name clashes
The original and default behaviour is that the option values are stored as properties on the program, and the action handler is passed a command object with the options values stored as properties. This is very convenient to code, but the downside is possible clashes with existing properties of Command.
There are two new routines to change the behaviour, and the default behaviour may change in the future:
storeOptionsAsProperties
: whether to store option values as properties on command object, or store separately (specify false) and access using.opts()
passCommandToAction
: whether to pass command to action handler, or just the options (specify false)
(example)
program ; program name'my-program-name' ; program action { console; }; program; const programOptions = program;console;
TypeScript
The Commander package includes its TypeScript Definition file.
If you use ts-node
and stand-alone executable subcommands written as .ts
files, you need to call your program through node to get the subcommands called correctly. e.g.
node -r ts-node/register pm.ts
createCommand()
This factory function creates a new command. It is exported and may be used instead of using new
, like:
const createCommand = ;const program = ;
createCommand
is also a method of the Command object, and creates a new command rather than a subcommand. This gets used internally
when creating subcommands using .command()
, and you may override it to
customise the new subcommand (examples using subclass and function).
--harmony
Node options such as You can enable --harmony
option in two ways:
- Use
#! /usr/bin/env node --harmony
in the subcommands scripts. (Note Windows does not support this pattern.) - Use the
--harmony
option when call the command, likenode --harmony examples/pm publish
. The--harmony
option will be preserved when spawning subcommand process.
Debugging stand-alone executable subcommands
An executable subcommand is launched as a separate child process.
If you are using the node inspector for debugging executable subcommands using node --inspect
et al,
the inspector port is incremented by 1 for the spawned subcommand.
If you are using VSCode to debug executable subcommands you need to set the "autoAttachChildProcesses": true
flag in your launch.json configuration.
Override exit handling
By default Commander calls process.exit
when it detects errors, or after displaying the help or version. You can override
this behaviour and optionally supply a callback. The default override throws a CommanderError
.
The override callback is passed a CommanderError
with properties exitCode
number, code
string, and message
. The default override behaviour is to throw the error, except for async handling of executable subcommand completion which carries on. The normal display of error messages or version or help
is not affected by the override which is called after the display.
program;tryprogram;catch err// custom processing...
Examples
const program = ; program version'0.1.0' ; program description'run setup commands for all envs' action{ const mode = optionssetup_mode || "normal"; env = env || 'all'; console; }; program description'execute the given remote cmd' action{ console; }; program;
More Demos can be found in the examples directory.
License
Support
Commander 5.x is fully supported on Long Term Support versions of Node, and is likely to work with Node 6 but not tested. (For versions of Node below Node 6, use Commander 3.x or 2.x.)
The main forum for free and community support is the project Issues on GitHub.
Commander for enterprise
Available as part of the Tidelift Subscription
The maintainers of Commander and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. Learn more.