parallel

CLI tool to execute shell commands in parallel.

Loosely based on GNU parallel command.

Installation

Using npm:

$ npm install -g parallel

Usage

# Pass input lines as command-line arguments
input | parallel [options] cmd [cmd-options] {} > output

# Pipe input lines through the jobs stdin
input | parallel [options] --pipe cmd [cmd-options] > output

Options

-j, --jobs <n>          Max processes to run in parallel (0 for ∞) [default CPUs]
-n, --max-args <args>   Number of input lines per command line [default 1]
-d, --delimiter <delim> Input items are terminated by delim [default \n]
-0, --null              Use NUL as delimiter, alias for -d $'\\0'
-q, --quote             Quote each input line in case they contain special caracters
-t, --trim              Removes spaces, tabs and new lines around the input lines
-C, --colsep <regex>    Column separator for positional placeholders [default " "]
-a, --arg-file <file>   Use file as input source instead of stdin
-p, --pipe              Spread input lines to jobs via their stdin
-D, --dry-run           Print commands to run without running them
--bg                    Run commands in background and exit
--delay <secs>          Wait before starting new jobs, secs can be less than 1 [default 0]
--timeout <secs>        If the command runs longer than secs it gets killed with SIGTERM [default 0]
--halt-on-error         Kill all jobs and exit if any job exits with a code other than 0 [default false]
-v, --verbose           Output timing information to stderr
-s, --shell             Wrap command with shell (supports escaped pipes, redirection, etc.) [experimental]
--help                  Print this message and exit
--version               Print the comand version and exit

Arguments placeholders

Unless --pipe is used, the input lines will be sent to jobs as command-line arguments. You can include placeholders and they will be replaced with each input line. If no placeholder is found, input lines will be appended to the end as last arguments. Everything around each placeholder will be repeated for each input line. Use quotes to include spaces or escape them with backslashes.

{}   input line
{.}  input line without extension
{/}  basename of the input line
{//} dirname of the input line
{/.} basename of the input line without extension
{n}  nth input column, followed by any operator above (f.e {2/.})
{#}  sequence number of the job to run [1, ∞]
{%}  job slot number [1, --jobs]

Input from command-line arguments

Input can be provided as command-line arguments preceeded by a :::. Each argument will be considered a separate input line. If you include several :::, parallel will use all the permutations between them as input lines. While GNU´s version also permutates stdin and input files, this version won't. Check examples (6) and (7) to see this in action.

Examples

# (1) Use all CPUs to grep a file
cat data.txt | parallel -p grep pattern > out.txt

# (2) Use all CPUs to gunzip and concat files to a single file, 10 per process at a time
find . -name '*.gz' | parallel -n10 gzip -dc {} > out.txt

# (3) Download files from a list, 10 at a time with all CPUs, use the URL basename as file name
cat urls.txt | parallel -j10 curl {} -o images/{/}

# (4) Generate 100 URLs and download them with `curl` (uses experimental --shell option)
seq 100 | parallel -s curl http://xyz.com/image_{}.png \> image_{}.png

# (5) Move each file to a subdir relative to their current dir
find . -type f | parallel mkdir -p {//}/sub && mv {} {//}/sub/{/}

# (6) Show how to provide input as command-line arguments and what the order is
echo 4 | parallel -j1 echo ::: 1 2 3

# (7) Rename extension from all txt to log
parallel mv {} {.}.log ::: *.txt

# (8) Showcase non-positional placeholders
find . -type f | parallel echo "file={} noext={.} base={/} base_noext={/.} dir={//} jobid={#} jobslot={%}"

# (9) Showcase positional placeholders
echo A~B.ext~C~D | parallel -C '~' echo {4}+{3}+{2.}+{1}

Command-line options

Once a command-line parameter that is not an option is found, then the "command" starts. parallel supports command-line options in all these formats (all equivalent):

• --trim --jobs 2
• --trim --jobs=2
• -t -j 2
• -tj 2
• -tj2

Exit code

Just like GNU parallel does, the exit code will be the amount of jobs that failed (up to 101). It means that if any job fails, "global" exit code will be non-zero as well. You can add --halt-on-error to abort as soon as one job fails.

Differences with GNU parallel

• Added aliases to some options: -p -> --pipe, -D -> --dry-run
• --round-robin is implicit when --pipe is used
• This module does support piped input and ::: arguments together unlike GNU's
• This module won't permutate input from ::: and from stdin or --arg-file
• GNU's -m can be achieved here with --max-args=0 to distribute all input lines evenly among --jobs
• --shell was added to allow pipes, redirection, etc
• --trim doesn't support <n|l|r|lr|rl>, it trims all spaces, tabs and newlines from both sides
• --halt-on-error doesn't support any option, it exits as soon as one job fails
• A ton of missing options that I consider less useful
• --plus placeholders are not supported
• Many more

ToDo

• Implement backpressure to pause input if output is overwhelmed
• Support --header for working with CSV-like files
• Should it permutate lines from stdin and --arg-file ?
• Could implement --keep-order
• Use node-shell-quote for --dry-run and --shell?
• Clean up jobs module, maybe create a job module with some of its logic
• Maybe avoid pre-spawning jobs when piping. Spawn on demand when overwhelmed, support --delay there too
• Support multiple -a? can be achieved with cat a b c though, maybe it's pointless

License

Copyright (c) 2016, Ariel Flesler All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

• Neither the name of the organization nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.