$ npm install -g parallel

parallel [options] [command [arguments]] < list_of_arguments
parallel [options] [command [arguments]] (::: arguments)...
cat ... | parallel --pipe [options] [command [arguments]]

-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]
-X, --xargs             Multiple arguments with context replace
-d, --delimiter <delim> Input items are terminated by delim [default \n]
-0, --null              Use NUL as delimiter
-q, --quote             Quote each input line in case they contain special caracters
--quote-all             Quote each input line in case they contain special caracters (alias for --quote)
--trim                  Removes spaces, tabs and new lines around the input lines
-t, --print-commands    Print the jobs which parallel is running to stderr
-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
--block <size>          Size of each block in --pipe mode (e.g., 1M, 10K)
-D, --dry-run           Print commands to run without running them
--tag                   Prefix each line of output with the argument that generated it
--shuf                  Randomize the order of jobs
-k, --keep-order        Keep same order as input
--joblog <file>         Log job details (start time, runtime, exit code, command) to file
--bg                    Run commands in background and exit
--delay <secs>          Wait before starting new jobs, secs can be less than 1
--timeout <secs>        If the command runs for longer than secs it will get killed with SIGTERM
--halt-on-error         Kill all jobs and exit if any job exits with a code other than 0
-v, --verbose           Print job commands and 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

{}     the input line
{.}    the input line without extension
{/}    the basename of the input line
{//}   the dirname of the input line
{/.}   the basename of the input line without extension
{#}    the sequence number of the job to run, [1,]
{%}    the job slot number [1, --jobs]
{..}   the input line without two extensions (e.g., file.tar.gz → file)
{...}  the input line without three extensions (e.g., file.tar.gz.backup → file)
{/..}  the basename without two extensions (e.g., path/file.tar.gz → file)
{/...} the basename without three extensions (e.g., path/file.tar.gz.backup → file)
{+/}   the number of "/" in the input line
{+.}   the number of "." in the input line
{n}    nth input column, followed by any operator above (f.e {2/.})

{ext}  the extension of the input line
{trim} the input line with leading/trailing whitespace removed
{v}    lower case the value
{^}    upper case the value
{t}    current time as a number
{T}    current time in ISO as a string
{d}    current date in ISO format
{r}    random number between 100000 and 999999
{md5}  MD5 hash of the input line
{len}  the length of the input line in characters
{wc}   the word count of the input line

# (1) Download files simultaneously 
echo -e "https://example.com/file1.zip\nhttps://example.com/file2.zip" | parallel curl -L {} -o downloads/{/}

# (2) Convert video files using all CPU cores
parallel ffmpeg -i {} -c:v libx264 converted/{.}.mp4 ::: *.avi

# (3) Compress large log files efficiently
find /var/log -name "*.log" -size +100M | parallel gzip {}

# (4) Demonstrate path manipulation placeholders
echo -e "/home/user/document.pdf\n/tmp/archive.tar.gz" | \
  parallel echo "Full: {} | Dir: {//} | File: {/} | Name: {/.} | Ext: {ext}"

# (5) Multi-extension removal (GNU --plus compatibility)
echo -e "project.tar.gz\nbackup.tar.gz.old" | \
  parallel echo "File: {} | 1 ext: {.} | 2 ext: {..} | 3 ext: {...}"

# (6) Count characters in paths and filenames
echo -e "/deep/nested/path/file.min.js\nshallow.txt" | \
  parallel echo "File: {} | Slashes: {+/} | Dots: {+.} | Length: {len}"

# (7) Process CSV data with column placeholders
echo -e "John,28,Engineer\nSarah,32,Designer" | \
  parallel -C ',' echo "Employee: {1} ({2} years old) works as {3}"

# (8) Clean whitespace from messy input
printf "  Alice  \n\t  Bob\t\n" | parallel echo "Original: '{}' | Cleaned: '{trim}'"

# (9) Transform text case and count words
echo -e "Hello World\nFOO BAR" | parallel echo "Text: {} | Lower: {v} | Upper: {^} | Words: {wc}"

# (10) Preserve output order despite varying job times
seq 5 | parallel -k "sleep $((6 - {})); echo 'Job {} done'"

# (11) Limit concurrency and log job details
parallel -j 2 --joblog build.log "sleep 1; echo 'Built {}'" ::: app1 app2 app3

# (12) Tag output lines with their input source
echo -e "server1\nserver2" | parallel --tag "ping -c 1 {}"

# (13) Process large files in manageable chunks
cat huge_dataset.csv | parallel --pipe --block 10M "wc -l"

# (14) Group multiple arguments per command
echo -e "file1\nfile2\nfile3\nfile4" | parallel -X echo "Batch:" {}

# (15) Randomize execution order for testing
seq 10 | parallel --shuf --dry-run "echo 'Processing {}'"

# (16) Generate all combinations from multiple input sources
parallel echo "Operation: {} on {}" :::: <(echo -e "backup\narchive") :::: <(echo -e "db.sql\nconfig.json")

# (17) Use built-in time and random placeholders
parallel "echo 'Job {} at {T} (ID: {r})'" ::: task1 task2