Conditions

Conditions are executed before the action handlers to control and guarantee its execution.

Conditions if and unless determine the execution of the handler by their values or the result of its resolving in case of function. Other conditions exist and are prefixed with if_ or unless_ for their negation. Multiple conditions can be combined, in which case, all of them must pass.

The following example represents updating a file. It contains 2 conditions applied to nikita.file action that writes to a file. The first condition, if_exists, passes if the file exists. The second one, if, verifies the owner of the file is the same user who is running the Node.js process. Note, the fs.base.stat action returning information about a file is called with the enabled "relax" behavior to make it tolerant to an error in case of lack of the file:

(async () => {
  var {$status} = await nikita
  // Update file content
  .file({
    $if_exists: '/tmp/nikita/a_file',    $if: async function({config}) {      // Get the file information      const {stats} = await this.fs.base.stat({        // Don't throw an error in case of lack of the file        $relax: 'NIKITA_FS_STAT_TARGET_ENOENT',        target: config.target      })      // Pass the condition if the user is the owner      return stats && stats.uid == process.getuid() ? true : false    },    target: '/tmp/nikita/a_file',
    content: 'hello'
  })
  console.info('File is updated:', $status)
})()

if

Condition the execution of the action handlers to a user defined condition interpreted as true.

When the if value is:

• a boolean, a string, a number, null or undefined, its value determines the handler execution.

• a function, the argument is a context object including the config object and the handler is run synchronously.

• an array, all its elements must positively resolve for the condition to pass.

For example, the content of the file "/tmp/nikita/a_file" will be updated because all the conditions succeed:

(async () => {
  var {$status} = await nikita
  // Update file content
  .file({
    $if: [      'ok',      1,      true,      ({config}) => { return config.content === 'hello' }    ],    target: '/tmp/nikita/a_file',
    content: 'hello'
  })
  console.info('File is updated:', $status)
})()

unless

Condition the execution of an action to a user-defined condition interpreted as false. It is a negation of the if property.

When the unless value is:

• a boolean, a string, a number, null or undefined, its value determine the handler execution.

• a function, the argument is a context object including the config object and the handler is run synchronously.

• an array, all its elements must negatively resolve for the condition to pass.

For example, the content of the file "/tmp/nikita/a_file" will be updated because all the conditions failed:

(async () => {
  var {$status} = await nikita
  // Update file content
  .file({
    $unless: [      '',      0,      false,      null,      undefined,      function({config}){ return config.content !== 'hello' },    ],    target: '/tmp/nikita/a_file',
    content: 'hello'
  })
  console.info('File is updated:', $status)
})()

if_execute

Conditions the execution of an action if a shell command succeeds.

The if_execute value could be a string a an array of strings. It is evaluated as a single shell command or a list of commands.

For example, the content of the file "/tmp/nikita/a_file" will be updated if "/tmp/flag" is an existing file:

(async () => {
  var {$status} = await nikita
  // Update file content
  .file({
    $if_execute: '[ -f "/tmp/flag" ]',    target: '/tmp/nikita/a_file',
    content: 'hello'
  })
  console.info('File is updated:', $status)
})()

unless_execute

Conditions the execution of an action unless a shell command succeeds. It is a negation of the if_execute property.

The unless_execute value could be a string a an array of strings. It is evaluated as a single shell command or a list of commands.

For example, the content of the file "/tmp/nikita/a_file" will be updated if "/tmp/flag" is not an existing file:

(async () => {
  var {$status} = await nikita
  // Update file content
  .file({
    $unless_execute: '[ -f "/tmp/flag" ]',    target: '/tmp/nikita/a_file',
    content: 'hello'
  })
  console.info('File is updated:', $status)
})()

if_exists

Conditions the execution of an action if a file or a directory exists.

The if_exists value could be a string a an array of strings. It is evaluated as paths to files or directories to check for existence.

For example, the content of the file "/tmp/nikita/a_file" will be updated if the file exists and if "/tmp/flag" exists as well:

(async () => {
  var {$status} = await nikita
  // Update file content
  .file({
    $if_exists: [      '/tmp/nikita/a_file',      '/tmp/flag'    ],    target: '/tmp/nikita/a_file',
    content: 'hello'
  })
  console.info('File is updated:', $status)
})()

unless_exists

Conditions the execution of an action unless a file or a directory exists. It is a negation of the if_exists property.

The unless_exists value could be a string a an array of strings. It is evaluated as paths to files or directories to check for existence.

For example, the content of the file "/tmp/nikita/a_file" will be updated if the file "/tmp/flag" doesn't exist:

(async () => {
  var {$status} = await nikita
  // Update file content
  .file({
    $unless_exists: '/tmp/flag'    target: '/tmp/nikita/a_file',
    content: 'hello'
  })
  console.info('File is updated:', $status)
})()