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Command Line Error

Unified error handling for command line interfaces.

About

Most command line programs under-utilize the ability to use multiple non-zero exit codes to indicate the type of error encountered, typically most programs exit with an exit status of 1 which gives no indication of what type of error occured.

The benefit of using multiple non-zero exit codes is that it is much easier to programatically determine the type of error that occured when invoking a program from another program without parsing stderr.

If a program documents it's exit status codes then a callee can ignore stderr and provide it's own indication of the type of error that occured.

This module is a set of helper functions and an error class designed to help creators of command line interfaces to structure their error handling around pre-defined error instances with different non-zero exit codes.

Features

• Seamless integration with ttycolor
• Exit status codes associated with an Error instance
• Message replacement parameters at definition or runtime
• Auto-incrementing exit status codes
• Load error definitions from locale aware json documents

Installation

npm install cli-error

Developers

git clone https://github.com/freeformsystems/cli-error.git
cd cli-error && npm install && npm test

Test

npm test

Examples

The bin directory contains example programs.

Usage

Definition

Use define and raise to use auto-incrementing exit status codes and reference errors by identifier, adapted from the argv example executable.

./bin/argv; echo $?;

var clierr = require('cli-error');
var define = clierr.define, raise = clierr.raise, errors = clierr.errors;
define('EARGLENGTH', 'too few arguments');
if(process.argv.length < 3) {
  raise(errors.EARGLENGTH);
}

Manual

If you prefer you can create errors as needed, adapted from the manual example executable.

./bin/manual; echo $?;

var clierr = require('cli-error'), Error = clierr.error;
var err = new Error('fatal: %s not found', 128, ['file.json']);
// print formatted message to stderr
err.error();
// use the error exit status code 
err.exit();

API

Configuration

Configure the options for the module by passing an object when requiring the module:

var clierr = require('..')({name: 'program'});

• name: The name for the error instances, default is basename(process.argv[1]).
• start: A number indicating the start when auto-incrementing exit status codes, default 64.
• log: String path to a log file or a WritableStream.
• flags: Flags to use when creating the log file stream (default is a), only applies when the log property is a string.
• prefix: A prefix for messages used when printing errors using the console methods. May be a boolean true to use name as the prefix (like standard error messages), a string or a function that returns a prefix.
• lang: Final fallback language identifer used when loading language files, default en.
• locales: Directory containing the locale specific error definition files, default if a 'locales' directory relative to the directory containing the executable.
• lc: Array of environment variable names to test first before finding the first LC variable when loading language definitions. Default is ['LC_ALL', 'LC_MESSAGES'].

Module

clear()

Clear all error definitions.

open([file, flags])

Opens a log file (or stream) and redirects the console methods to write to the log file.

• file: The file path or stream, default is config.log.
• flags: The file flags when opening the file, default is a.

close()

Closes an existing log file stream and restore the console.error and console.warn functions.

config

Map of configuration information.

CliError

Reference to the CliError class.

define(key, message, [parameters], [code])

Define an error by named key.

• key: The error key.
• message: The error message.
• parameters: Array of message replacement parameters (optional).
• code: Specific exit status code for the error (optional).

Returns an ErrorDefinition instance.

ErrorDefinition

Reference to the ErrorDefinition class.

errors

Map of error definitions.

exit(err, trace, ...)

Exit the program with a fatal error from an error definition.

• err: The error definition.
• trace: Whether to print the stack trace.
• ...: Message replacement parameters.

file([options], callback)

Load error definitions from a locale specific JSON document respecting the LC environment variables.

This method implements a merge stategy so that error messages are always available , unless the configuration property lang has been changed and options.fallback has not been specified then the fallback file path will be locales/en.json relative to the directory containing the executable.

• options: An object containing file load options.
• callback: A callback function.

The callback signature is function(err, file, errors, lang).

Options

• lang: Specify a language identifier, use this if you know the users language ahead of time (for example, your application provides a configuration option for the locale). If lang is specified the LC environment variables are not searched.
• fallback: Fallback language identifier, overrides config.lang.
• locales: Directory containing error definition files, overrides config.locales.
• lc: Array of environment variable names, overrides config.lc.

load(source)

Load error definitions from a source array.

raise(err, ...)

• err: A CliError instance.
• ...: Message replacement parameters.

Raise an error from an error definition. If there are no defined listeners for uncaughtException this method will print the formatted error message, using console.error and exit with the status code associated with the error instance. The stack trace is not printed to stderr.

warn(err, trace, ...)

Print a warn message from an error definition.

• err: The error definition.
• trace: Whether to print the stack trace.
• ...: Message replacement parameters.

CliError

An Error subclass.

new CliError(message|error, [code], [parameters], [name])

• message|error: A string message or another Error to wrap.
• code: The exit status code.
• parameters: Message replacement parameters.
• name: A specific name for the error.

code

The exit status code.

error(trace, ...)

Print an error message to stderr optionally including a stack trace.

• trace: Whether to print the stack trace.
• ...: Message replacement parameters.

exit()

Exit the program with the exit status code associated with the error instance.

format([...])

Retrive a formatted message using the arguments passed to format() with the message assigned to the error.

key

The identifier for the error, only available when created from an error definition.

info

Array of raw stack trace information, see the v8 stack trace api for more information.

message

The error message.

name

The name for the instance, this will be the name of the program being executed unless configured with a different name.

parameters

Array of message parameters set when the error was defined.

pop()

Remove the last element in the stack trace and update the underlying data.

####shift()

Remove the first element in the stack trace and update the underlying data.

source

A source Error instance if the error wraps another error.

####splice(index, amount)

Remove elements from the stack trace and update the underlying data.

• index: The start index.
• amount: The number of items to delete.

Note unlike Array.splice() this method does not allow inserting elements.

stack

String representation of the stack trace when the error was instantiated.

stacktrace

Array of stack trace lines with leading and trailing whitespace removed.

stringify(trace, ...)

Get a JSON string representation of this error instance.

• trace: Whether to print the stack trace.
• ...: Message replacement parameters.

toObject(trace, ...)

Get an object suitable for passing to JSON.stringify.

• trace: Whether to print the stack trace.
• ...: Message replacement parameters.

warn(trace, ...)

Print a warn message to stderr optionally including a stack trace.

• trace: Whether to print the stack trace.
• ...: Message replacement parameters.

ErrorDefinition

An error definfition is used to reference an error by identifier (key).

new ErrorDefinition(key, message, code, parameters)

• key: The identifier for the error definition.
• message: A string message.
• code: The exit status code.
• parameters: Message replacement parameters.

code

The exit status code.

key

The key used to identify the error.

message

The error message.

parameters

Array of message replacement parameters.

toError([e], [parameters], [code])

Convert an error definition to a CliError instance.

• e: A source error.
• parameters: An array of message replacement parameters.
• code: An exit status code.

License

Everything is MIT. Read the license if you feel inclined.