A tool to execute commands in parallel (something like GNU parallel).

Written to try out the Little language. And also Rust.

ljobs [OPTIONS...] COMMAND [CMD-ARGS...] ::: TASKS...
ljobs [OPTIONS...] COMMAND [CMD-ARGS...] < TASKS

ljobs will run the given command for each task. Multiple commands can run in parallel.

Each task is an arbitrary string, commonly a file name or other input. If the ::: form is used then tasks are given directly on the command line. Otherwise, tasks are read from standard input, one line per task.

These strings are replaced in command arguments:

{}      replaced by the task argument
{.}     replaced by task without extension
{/}     replaced by basename of task
{//}    replaced by dirname of task
{/.}    replaced by basename of task without extension
{#}     replaced by the task number, counting from 0

If none of the strings occur in a command argument then the task is appended as the last argument of the command, i.e. {} is implied.

These are the options to ljobs itself.

• -j NUM, --jobs NUM

  Specify number of job slots. Defaults to number of processors detected.

• -k, --keep-going

  Continue starting tasks even if a previous task failed.

• -c

  Execute command with the shell interpreter given by the SHELL environment variable, or else /bin/sh. The command arguments are passed as positional parameters $1, $2, etc.

• -v, --verbose

  Enable verbose output.

• -n, --dry-run

  Print commands to be executed but do not run them.

• -h, --help

  Show usage message.

• --

  End option processing.

The standard output and standard error outputs of a running command are buffered in temporary files, and only output once the command stops. This prevents interleaving of outputs for different tasks.

With -k or --keep-going the exit status is

0       all tasks executed successfully
1-253   number of failed tasks
254     more than 253 failed tasks
255     other error

Without -k or --keep-going the exit status is

0       all tasks executed successfully
1-255   exit status of a failed task

ljobs oggenc ::: *.flac

ljobs lame {} {.}.mp3 ::: *.wav

• Does not catch signals. This seems to require a Tcl extension.

Peter Wang