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>          Number of processes to spawn [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              Trims the input of leading and trailing spaces and tabs
-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
--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]
-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 line. Use quotes to include spaces.

{}   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]

Examples

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

# Use all CPUs to gunzip and concat files to a single file, 10 per process at a time
find . -name "*.gz" -print0 | parallel -0n 10 gzip -dc {} > out.txt

# Download 10 images at a time, use the URL basename as file name
cat urls.txt | parallel -j 10 curl {} -o images/{/}

# Generate 100 URLs and download them with `curl` (uses experimental --shell option)
echo {001..100} | parallel -tsd " " curl http://xyz.com/image_{}.png \> image_{}.png

# Rename extension from all txt to log
find . -name '*.txt' | parallel mv {} {.}.log

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

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

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

Differences with GNU parallel

• -p added as an alias of --pipe
• --round-robin is implicit when --pipe is used
• --max-args 0 here means 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
• A ton of missing options that I consider less useful
• Some placeholders aren't supported
• Many more

ToDo

• Support more options from GNU parallel
• Support more placeholders
• Maybe support ::: and ::::, seems pointless
• Support multiple -a, can be achieved with cat a b c though
• Implement backpressure to pause input if output is overwhelmed
• Change option parser to support this format: -j2 ?
• Show help when nothing is piped in, process.stdin.isTTY not working as expected
• Maybe avoid pre-spawning jobs when piping. Spawn on demand when overwhelmed, support --delay there too
• Support --jobs=0 for unlimited. Easy except when piping or when --max-args=0
• Should default behavior of -n 0 only happen if -m or -xargs, like on GNU?

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.