docs » hs.task


Execute processes in the background and capture their output

Notes:

  • This is not intended to be used for processes which never exit. While it is possible to run such things with hs.task, it is not possible to read their output while they run and if they produce significant output, eventually the internal OS buffers will fill up and the task will be suspended.
  • An hs.task object can only be used once

API Overview

API Documentation

Functions

new

Signature hs.task.new(launchPath, callbackFn[, streamCallbackFn, arguments]) -> hs.task object
Type Function
Description Creates a new hs.task object
Parameters
  • launchPath - A string containing the path to an executable file. This must be the full path to an executable and not just an executable which is in your environment's path (e.g. `/bin/ls` rather than just `ls`).
  • callbackFn - A callback function to be called when the task terminates, or nil if no callback should be called. The function should accept three arguments:
  • exitCode - An integer containing the exit code of the process
  • stdOut - A string containing the standard output of the process
  • stdErr - A string containing the standard error output of the process
  • streamCallbackFn - A optional callback function to be called whenever the task outputs data to stdout or stderr. The function must return a boolean value - true to continue calling the streaming callback, false to stop calling it. The function should accept three arguments:
  • task - The hs.task object
  • stdOut - A string containing the standard output received since the last call to this callback
  • stdErr - A string containing the standard error output received since the last call to this callback
  • arguments - An optional table containing command line arguments for the executable
Returns
  • An `hs.task` object
Notes
  • The arguments are not processed via a shell, so you do not need to do any quoting or escaping. They are passed to the executable exactly as provided.

Methods

closeInput

Signature hs.task:closeInput() -> hs.task object
Type Method
Description Closes the task's stdin
Parameters
  • None
Returns
  • The hs.task object
Notes
  • This should only be called on tasks with a streaming callback - tasks without it will automatically close stdin when any data supplied via `hs.task:setInput()` has been written
  • This is primarily useful for sending EOF to long-running tasks

environment

Signature hs.task:environment() -> environment
Type Method
Description Returns the environment variables as a table for the task.
Parameters
  • None
Returns
  • a table of the environment variables for the task where each key is the environment variable name.

interrupt

Signature hs.task:interrupt() -> hs.task object
Type Method
Description Interrupts the task
Parameters
  • None
Returns
  • The `hs.task` object
Notes
  • This will send SIGINT to the process

isRunning

Signature hs.task:isRunning() -> boolean
Type Method
Description Test if a task is still running.
Parameters
  • None
Returns
  • true if the task is running or false if it is not.
Notes
  • A task which has not yet been started yet will also return false.

pause

Signature hs.task:pause() -> boolean
Type Method
Description Pauses the task
Parameters
  • None
Returns
  • If the task was paused successfully, returns the task object; otherwise returns false
Notes
  • If the task is not paused, the error message will be printed to the Hammerspoon Console
  • This method can be called multiple times, but a matching number of `hs.task:resume()` calls will be required to allow the process to continue

pid

Signature hs.task:pid() -> integer
Type Method
Description Gets the PID of a running/finished task
Parameters
  • None
Returns
  • An integer containing the PID of the task
Notes
  • The PID will still be returned if the task has already completed and the process terminated

resume

Signature hs.task:resume() -> boolean
Type Method
Description Resumes the task
Parameters
  • None
Returns
  • If the task was resumed successfully, returns the task object; otherwise returns false
Notes
  • If the task is not resumed successfully, the error message will be printed to the Hammerspoon Console

setCallback

Signature hs.task:setCallback(fn) -> hs.task object
Type Method
Description Set or remove a callback function for a task.
Parameters
  • fn - A function to be called when the task completes or is terminated, or nil to remove an existing callback
Returns
  • the hs.task object

setEnvironment

Signature `hs.task:setEnvironment(environment) -> hs.task object false` </span>
Type Method
Description Sets the environment variables for the task.
Parameters
  • environment - a table of key-value pairs representing the environment variables that will be set for the task.
Returns
  • The hs.task object, or false if the table was not set (usually because the task is already running or has completed)

setInput

Signature hs.task:setInput(inputData) -> hs.task object
Type Method
Description Sets the standard input data for a task
Parameters
  • inputData - Data, in string form, to pass to the task as its standard input
Returns
  • The hs.task object
Notes
  • This method can be called before the task has been started, to prepare some input for it (particularly if it is not a streaming task)
  • If this method is called multiple times, any input that has not been passed to the task already, is discarded (for streaming tasks, the data is generally consumed very quickly, but for now there is no way to syncronise this)

setStreamingCallback

Signature hs.task:setStreamingCallback(fn) -> hs.task object
Type Method
Description Set a stream callback function for a task
Parameters
  • fn - A function to be called when the task outputs to stdout or stderr, or nil to remove a callback
Returns
  • The hs.task object
Notes
  • For information about the requirements of the callback function, see `hs.task.new()`
  • If a callback is removed without it previously having returned false, any further stdout/stderr output from the task will be silently discarded

setWorkingDirectory

Signature `hs.task:setWorkingDirectory(path) -> hs.task object false` </span>
Type Method
Description Sets the working directory for the task.
Parameters
  • path - a string containing the path you wish to be the working directory for the task.
Returns
  • The hs.task object, or false if the working directory was not set (usually because the task is already running or has completed)
Notes
  • You can only set the working directory if the task has not already been started.
  • This will only set the directory that the task starts in. The task itself can change the directory while it is running.

start

Signature `hs.task:start() -> hs.task object false` </span>
Type Method
Description Starts the task
Parameters
  • None
Returns
  • If the task was started successfully, returns the task object; otherwise returns false
Notes
  • If the task does not start successfully, the error message will be printed to the Hammerspoon Console

terminate

Signature hs.task:terminate() -> hs.task object
Type Method
Description Terminates the task
Parameters
  • None
Returns
  • The `hs.task` object
Notes
  • This will send SIGTERM to the process

terminationReason

Signature `hs.task:terminationReason() -> exitCode false` </span>
Type Method
Description Returns the termination reason for a task, or false if the task is still running.
Parameters
  • None
Returns
  • a string value of "exit" if the process exited normally or "interrupt" if it was killed by a signal. Returns false if the termination reason is unavailable (the task is still running, or has not yet been started).

terminationStatus

Signature `hs.task:terminationStatus() -> exitCode false` </span>
Type Method
Description Returns the termination status of a task, or false if the task is still running.
Parameters
  • None
Returns
  • the numeric exitCode of the task, or the boolean false if the task has not yet exited (either because it has not yet been started or because it is still running).

waitUntilExit

Signature hs.task:waitUntilExit() -> hs.task object
Type Method
Description Blocks Hammerspoon until the task exits
Parameters
  • None
Returns
  • The `hs.task` object
Notes
  • All Lua and Hammerspoon activity will be blocked by this method. Its use is highly discouraged.

workingDirectory

Signature hs.task:workingDirectory() -> path
Type Method
Description Returns the working directory for the task.
Parameters
  • None
Returns
  • a string containing the working directory for the task.
Notes
  • This only returns the directory that the task starts in. If the task changes the directory itself, this value will not reflect that change.

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