@percy/cli-command

Percy CLI command parser and runner.

• Usage
• Options
  • Args
  • Flags
  • Percy

Usage

The command function accepts a name, definition, and callback and returns a runner function that accepts an array of command-line arguments.

const { command } = require('@percy/cli-command');

// example command runner
const example = command('example', {
  description: 'Example command description',
  // positional arguments
  args: [
    { name: 'one' }
  ],
  // flags and options
  flags: [
    { name: 'foo' }, // boolean by default
    { name: 'bar', type: 'string' }
  ],
  // shows in help output
  examples: [
    // $0 will be replaced by the command name
    '$0 --foo --bar baz qux'
  ]
}, ({ flags, args }) => {
  // see below for other available properties
  console.log({ flags, args });
});

// remove the script name from argv
example(process.argv.slice(2));

$ node ./example --foo --bar baz qux
{ flags: { foo: true, bar: 'baz' }, args: { one: 'qux' } }

Options

Only a command name is required. However, without any other options, a command will only show the default help output with global flags. A command's callback will be called when the resulting command runner is invoked with an array of command-line arguments. How those arguments are interpreted and parsed is defined by the command's definition.

• name — The command name shown in help output, also used to match nested commands.
• definition — A command definition object defines various options to control help output, the arguments parser, and other percy options.
  • description — The command description shown in help output.
  • usage — Custom command usage shown in help output.
  • examples — An array of example strings to show in help output.
  • version — A version string to display via a -V, --version flag.
  • commands — An array or function returning an array of nested subcommands.
  • flags — Optional flag arguments accepted by the command (see below).
  • args — Positional arguments accepted by the command (see below).
  • percy — Enable creation of a core percy instance (see below).
  • config — Automatic percy config registration (see below).
  • loose — Push unknown arguments to argv. A string value will log as a warning when unknown arguments are first encountered by the parser.
  • exitOnError — Call process.exit() if the command encounters an error while running.
• callback — The command callback invoked after the runner is called with command-line arguments and after those arguments are interpreted by the internal parser.

The callback argument can be a function, an async function, or an async generator function. Given an async generator function, the command becomes cancelable via process interruption and is able to clean up after itself using traditional try-catch error handling.

The callback function is invoked with a single argument containing various contextual properties according to the command definition:

• flags — An object containing key-value pairs of flag arguments interpreted by the parser as determined by the flag's respective definition (see below).
• args — An object containing key-value pairs of positional arguments interpreted by the parser as determined by the arg's respective definition (see below).
• argv — An array of unknown arguments that were not parsed due to either the loose option or the presence of an end-of-arguments delimiter (--).
• percy — An instance of @percy/core only present when a corresponding percy definition option is provided (see below).
• log — A @percy/logger group namespaced under the command's name. The initial loglevel is optionally determined by various global logging flags (--verbose, --silent, --quiet).
• exit — Utility function to stop the execution of a command from within the runner. Accepts an exit code (default 1) and an exit reason (default 'EEXIT: ${exitCode}'). The function will throw an error which can be handled, or let bubble where the presence of exitOnError will cause the process to exit with the provided exit code.

Flags

Each flag definition must contain either a name or a short option. By default, all flags will be interpreted as boolean flags and will produce an error if a value is provided. Setting the type option to anything other than 'boolean' will allow providing command-line values and error if one is not provided.

• name — The flag name (i.e. --flag-name).
• short — The flag short character (i.e. -s).
• type — The flag type as displayed in help output.
• default — The flag's default value when not provided.
• parse — A function used to parse any provided flag value.
• validate — A function that should throw an error when the provided flag value is invalid.
• attribute — A string or function returning a string to set the value at on the callback argument's flags property. Defaults to the camelcase name or short character.
• percyrc — A string to map this flag to percy config options (see below).
• deprecated — A boolean, string, or tuple used to warn about a deprecated flag and optionally map it to an alternate flag (see below).

Args

Positional args correspond to their definition index, so the arg definition at index 0 will match the first provided command-line argument that is not a flag or subcommand. By default, positional args are optional, but can be configured to be required or have default values.

• name — The arg name shown in help output.
• required — Indicate that this flag is required, which causes an error when not provided.
• default — The arg's default value when not provided.
• parse — A function used to parse the provided argument.
• validate — A function that should throw an error when the provided argument is invalid.
• attribute — A string or function returning a string to set the value at on the callback argument's args property. Defaults to camelcase name.
• percyrc — A string to map this arg to percy config options (see below).
• deprecated — A boolean, string, or tuple used to warn about a deprecated arg and optionally map it to a flag (see below).

Deprecations

When the deprecated option is true and the flag or positional arg has been provided by command-line arguments, a deprecation warning will be logged. A string value indicates the version in which this argument will be removed and is reflected in the deprecation message.

{ name: 'foo', deprecated: true }
// [percy] Warning: The '--foo' option will be removed in a future release.

{ name: 'foo', deprecated: 'v2.0.0' }
// [percy] Warning: The '--foo' option will be removed in v2.0.0.

{ name: 'foo', deprecated: ['v2.0.0', '--bar'] }
// [percy] Warning: The '--foo' option will be removed in v2.0.0. Use '--bar' instead.

{ name: 'foo', deprecated: ['v2.0.0', 'Use the config file option instead.'] }
// [percy] Warning: The '--foo' option will be removed in v2.0.0. Use the config file option instead.

Percy

The percy definition option accepts an object consisting of @percy/core options. The presence of this option will add shared percy flags to accepted command-line arguments and provide the command callback with a percy instance initialized with the provided options.

When the percy definition option is true, shared percy flags will not be accepted, but a default percy instance will still be provided to the command callback when run. Regardless of the percy option, if the environment variable PERCY_ENABLE is 0, the callback will not receive a percy instance (and can act accordingly).

• percy — Enables creation of a @percy/core instance initialized with provided options.
  • discoveryFlags — When false prevents percy discovery flags from being accepted, but will still allow other percy flags such as --config and --dry-run.
  • ... — All other options are passed along to the new percy instance.

Config

Acceptable percy config file options can be extended before the file is loaded via PercyConfig.addSchema() and PercyConfig.addMigration(). These functions can be called before the command is run to achieve the same effect as including them in the command definition. However, the presence of a percy definition option will also signal @percy/core config schemas and migrations to be automatically registered before the following options are registered.

• config — Percy config schemas and migrations to register while creating the command runner.
  • schemas — An array of percy config schemas to automatically register.
  • migrations — An array of percy config migrations to automatically register.

Additionally, flags and positional arguments that define a percyrc option will have their associated values mapped to a corresponding percy property that is used when initializing a @percy/core instance. Provided options are validated against config schemas and are made available on the command callback argument's percy.config property.