node_modules/@vue/cli-service/lib/commands/help.js

const { chalk } = require('@vue/cli-shared-utils')
const getPadLength = require('../util/getPadLength')

module.exports = (api, options) => {
  api.registerCommand('help', args => {
    const commandName = args._[0]
    if (!commandName) {
      logMainHelp()
    } else {
      logHelpForCommand(commandName, api.service.commands[commandName])
    }
  })

  function logMainHelp () {
    console.log(
      `\n  Usage: vue-cli-service <command> [options]\n` +
      `\n  Commands:\n`
    )
    const commands = api.service.commands
    const padLength = getPadLength(commands)
    for (const name in commands) {
      if (name !== 'help') {
        const opts = commands[name].opts || {}
        console.log(`    ${
          chalk.blue(name.padEnd(padLength))
        }${
          opts.description || ''
        }`)
      }
    }
    console.log(`\n  run ${
      chalk.green(`vue-cli-service help [command]`)
    } for usage of a specific command.\n`)
  }

  function logHelpForCommand (name, command) {
    if (!command) {
      console.log(chalk.red(`\n  command "${name}" does not exist.`))
    } else {
      const opts = command.opts || {}
      if (opts.usage) {
        console.log(`\n  Usage: ${opts.usage}`)
      }
      if (opts.options) {
        console.log(`\n  Options:\n`)
        const padLength = getPadLength(opts.options)
        for (const [flags, description] of Object.entries(opts.options)) {
          console.log(`    ${
            chalk.blue(flags.padEnd(padLength))
          }${
            description
          }`)
        }
      }
      if (opts.details) {
        console.log()
        console.log(opts.details.split('\n').map(line => `  ${line}`).join('\n'))
      }
      console.log()
    }
  }
}