CLI tool to execute shell commands in parallel.
Loosely based on GNU parallel command.
Using npm:
$ npm install -g parallel
# 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
-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
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 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.
# (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}
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
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
- 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 ajob
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 withcat a b c
though, maybe it's pointless
Copyright (c) 2016, Ariel Flesler All rights reserved.
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