$ 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) Process large datasets with all CPUs
cat big_data.csv | parallel --pipe --block 1M process_chunk.py

# (2) Convert images with preserved order (slow jobs finish out of order)  
echo -e "slow.jpg\nfast.jpg\nmedium.jpg" | parallel -k -s "sleep {#}; echo Converting {} to {.}.webp"

# (3) Download files from a list  
cat urls.txt | parallel curl -L {} -o downloads/{/}

# (4) Run tests in parallel with verbose output  
find tests -name "*.test.js" | parallel -t npm test {}

# (5) Compress files efficiently using all CPUs
find . -name '*.log' | parallel gzip {}

# (6) Process data with multiple arguments per job
echo -e "file1\nfile2\nfile3\nfile4" | parallel -X echo "Processing batch:" {}

# (7) Generate thumbnails with progress tracking
find photos -name "*.jpg" | parallel --tag convert {} thumbs/{/}

# (8) Batch process with job tracking
parallel --joblog processing.log ffmpeg -i {} {.}.mp4 ::: *.avi

# (9) Modern file operations with advanced placeholders  
echo -e "archive.tar.gz\nbackup.tar.gz" | parallel echo "Original: {} | Name: {/..} | Length: {len} chars"

# (10) Database operations in parallel
parallel -j 4 "psql -c \"UPDATE table SET status='processed' WHERE id={}\"" ::: {1..1000}

# (11) Rename files using transformation placeholders
parallel mv {} backup_{d}_{/} ::: *.txt

# (12) Process with column data
echo -e "John,25,Engineer\nJane,30,Designer" | parallel -C ',' echo "Name: {1}, Age: {2}, Job: {3}"

# (13) Keep output order for report generation
seq 10 | parallel -k "echo 'Processing item {}'; sleep $((RANDOM % 3)); echo 'Result: {}'"

# (14) Read arguments from multiple files (creates permutations)
parallel echo "Processing {} from {}" :::: servers.txt :::: tasks.txt

# (15) Handle special characters safely  
find . -name "* *" | parallel -q mv {} "cleaned/{/}"