A Bash function to run tasks in parallel and display pretty output as they complete.

Run three tasks concurrently:

concurrent \
    - 'My long task'   sleep 10 \
    - 'My medium task' sleep 5  \
    - 'My short task'  sleep 1

Run three tasks sequentially:

concurrent \
    - 'My long task'   sleep 10 \
    - 'My medium task' sleep 5  \
    - 'My short task'  sleep 1  \
    --sequential

Start the medium task after the short task succeeds:

concurrent \
    - 'My long task'   sleep 10 \
    - 'My medium task' sleep 5  \
    - 'My short task'  sleep 1  \
    --require 'My short task'   \
    --before  'My medium task'

Start the short task after both other tasks succeed:

concurrent \
    - 'My long task'   sleep 10 \
    - 'My medium task' sleep 5  \
    - 'My short task'  sleep 1  \
    --require 'My long task'    \
    --require 'My medium task'  \
    --before  'My short task'

Same as above, but shorter:

concurrent \
    - 'My long task'   sleep 10 \
    - 'My medium task' sleep 5  \
    - 'My short task'  sleep 1  \
    --require-all --before 'My short task'

Start the medium task and the long task after the short task succeeds:

concurrent \
    - 'My long task'   sleep 10 \
    - 'My medium task' sleep 5  \
    - 'My short task'  sleep 1  \
    --require 'My short task'   \
    --before  'My medium task'  \
    --before  'My long task'

Same as above, but shorter:

concurrent \
    - 'My long task'   sleep 10 \
    - 'My medium task' sleep 5  \
    - 'My short task'  sleep 1  \
    --require 'My short task' --before-all

Run the first two tasks concurrently, and then the second two tasks concurrently, and then the final three tasks concurrently.

concurrent \
    - 'Task 1'  sleep 3 \
    - 'Task 2'  sleep 3 \
    --and-then \
    - 'Task 3'  sleep 3 \
    - 'Task 4'  sleep 3 \
    --and-then \
    - 'Task 5'  sleep 3 \
    - 'Task 6'  sleep 3 \
    - 'Task 7'  sleep 3

If your command has a - argument, you can use a different task delimiter:

concurrent \
    + 'My long task'   wget -O - ... \
    + 'My medium task' sleep 5  \
    + 'My short task'  sleep 1

You can display extra information at the end of each task's status line by echoing to fd 3.

my_task() {
    ...
    echo "(extra info)" >&3
    ...
}

Take a look at demo.sh for more involved examples.

If you have a lot of dependencies between tasks, it's generally a good idea to perform a dry-run to ensure that the tasks are ordered as expected. Set the CONCURRENT_DRY_RUN environment variable to perform a dry-run.

By default, concurrent allows up to 50 concurrently-running tasks. Set the CONCURRENT_LIMIT environment variable to override this limit.

A neat trick is to set the limit to 1, essentially forcing a --sequential run, but with existing tasks between dependencies taken into account.

A limit less than 1 is treated as no limit.

If the number of tasks exceed the terminal height, the "compact display" will be activated. It can also be explicitly activated by setting the CONCURRENT_COMPACT environment variable to anything other than 0.

In this mode, each task is represented by a single character instead of an entire line. An execution summary is displayed above the tasks.

If the output is not attached to a tty, the "non-interactive" mode will be activated. It can also be explicitly activated by setting the CONCURRENT_NONINTERACTIVE environment variable to anything other than 0.

In this mode, each task is displayed as soon as it completes. Colors are also disabled.

By default, logs for each task will be created in ./logs/<timestamp>/. For example:

$ ls .logs/2016-02-02@00:09:07
0. Creating VM (0).log
1. Creating ramdisk (0).log
2. Enabling swap (0).log
3. Populating VM with world data (1).log
4. Spigot: Pulling docker image for build (1).log
5. Spigot: Building JAR (skip).log
6. Pulling remaining docker images (skip).log
7. Launching services (skip).log

To change this directory, set CONCURRENT_LOG_DIR before calling concurrent.

• bash >= 4.2 (for declare -g)
• cat
• cp
• date
• mkdir
• mkfifo
• mktemp
• mv
• sed
• tail
• tput

• 2.4.0
  • New: Gracefully switches to non-interactive mode when a tty is not present or if CONCURRENT_NONINTERACTIVE is non-zero.
• 2.3.3
  • Fix: Cursor no longer hidden when running nested.
• 2.3.2
  • Fix: Failing tasks with no output now exit with the correct status (credit: @uluyol).
• 2.3.1
  • Fix: Now clearing to end of line when printing extra status info after a task (credit: @fragmede).
• 2.3.0
  • New: Concurrency limit defaults to 50, unless overridden by CONCURRENT_LIMIT.
  • New: If the number of tasks exceed the terminal height (or CONCURRENT_COMPACT is set), each task will be displayed as a single character instead of a taking up an entire line.
  • New: Cursor now hidden while running.
  • Fix: Greatly improved speed of event loop. Especially noticeable for large numbers of tasks.
  • Fix: Namespaced command_* and prereq_* arrays so that they don't carry into the tasks.
• 2.2.1
  • Fix: Tasks not allowed to read from stdin.
• 2.2.0
  • New: Instances of concurrent can be nested without breaking.
  • New: Set custom log dir with CONCURRENT_LOG_DIR.
  • Fix: Works under Cygwin (special thanks to @FredDeschenes).
  • Fix: No longer requires GNU sed (gsed) on OS X.
  • Fix: Animation now uses a single process.
  • Fix: Extra status info is now merely bold instead of bold/white, which should be more visible on light terminal backgrounds.
• 2.1.0
  • New: New --and-then flag for dividing tasks into groups. All tasks in a group run concurrently, but all must complete before the next group may start (inspiration: fooshards on Reddit).
  • Fix: Removed extra backslashes in README (credit: bloody-albatross on Reddit)
• 2.0.1
  • Fix: kill is a bash builtin (credit: @ScoreUnder)
  • Fix: Require GNU sed on OS X (credit: @kumon)
  • Fix: Static analysis with shellcheck on push via Travis CI (credit: @xzovy)
  • Fix: Cleaner signal handling.
  • Fix: Simplified event loop.
• 2.0.0
  • New: Tasks can now display status updates by echoing to fd 3.
• 1.6.0
  • New: CONCURRENT_DRY_RUN environment variable runs sleep 3 instead of actual commands (and prints message).
• 1.5.2
  • Fix: Requirement loops disallowed.
• 1.5.1
  • Fix: Task is not allowed to require itself directly.
• 1.5.0
  • New: First argument is now the task delimiter.
• 1.4.1
  • Fix: Namespaced previously-missed function.
• 1.4.0
  • New: New --require-all and --before-all flags.
  • Fix: Namespaced all concurrent-related functions and variables.
  • Fix: Unsetting all concurrent-related functions and variables in the task's context.
  • Fix: Enforcing foreground in an interactive shell.
• 1.3.0
  • New: New --sequential flag, for when each task requires the previous.
• 1.2.0
  • New: Running tasks have an animated cursor.
  • Fix: Enforcing bash version 4.3.
  • Fix: Echo is re-enabled even if an internal error occurs.
• 1.1.6
  • Fix: Enforcing bash version 4.
• 1.1.5
  • Fix: Tasks now use original $PWD and $OLDPWD.
• 1.1.4
  • Fix: Tasks now use original $SHELLOPTS and $BASHOPTS.
• 1.1.3
  • Fix: Sanitizing forward slashes from log names.
• 1.1.2
  • Fix: Ensuring task status file exists even if an internal error occurs.
• 1.1.1
  • Fix: Task command may now have arguments starting with -.
• 1.1.0
  • New: Gracefully handling SIGINT.
  • Fix: Works on OS X too.
• 1.0.0
  • Initial working release.