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Master the command line, in one page

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The Art of Command Line

Note: I'm looking for a new (and potentially paid) lead author to help expand this to a more comprehensive Guide. While it's very popoular, it could be both deeper and more helpful. If you like to write and are close to being an expert on this material and willing to consider helping, please drop me a note at josh (0x40) holloway.com. –jlevy, Holloway

![curl -s 'https://raw.githubusercontent.com/jlevy/the-art-of-command-line/master/README.md' | egrep -o '\w+' | tr -d '`' | cowsay -W50](https://github.com/jlevy/the-art-of-command-line/raw/master/cowsay.png)

Fluency on the command line is a skill often neglected or considered arcane, but it improves your flexibility and productivity as an engineer in both obvious and subtle ways. This is a selection of notes and tips on using the command-line that we've found useful when working on Linux. Some tips are elementary, and some are fairly specific, sophisticated, or obscure. This page is not long, but if you can use and recall all the items here, you know a lot.

This work is the result of many authors and translators. Some of thisoriginallyappearedon Quora, but it has since moved to GitHub, where people more talented than the original author have made numerous improvements.Please submit a question if you have a question related to the command line. Please contribute if you see an error or something that could be better!

Meta

Scope:

  • This guide is both for beginners and the experienced. The goals are breadth (everything important), specificity (give concrete examples of the most common case), and brevity (avoid things that aren't essential or digressions you can easily look up elsewhere). Every tip is essential in some situation or significantly saves time over alternatives.
  • This is written for Linux, with the exception of the "macOS only" and "Windows only" sections. Many of the other items apply or can be installed on other Unices or macOS (or even Cygwin).
  • The focus is on interactive Bash, though many tips apply to other shells and to general Bash scripting.
  • It includes both "standard" Unix commands as well as ones that require special package installs -- so long as they are important enough to merit inclusion.

Notes:

  • To keep this to one page, content is implicitly included by reference. You're smart enough to look up more detail elsewhere once you know the idea or command to Google. Use
    apt
    ,
    yum
    ,
    dnf
    ,
    pacman
    ,
    pip
    or
    brew
    (as appropriate) to install new programs.
  • Use Explainshell to get a helpful breakdown of what commands, options, pipes etc. do.

Basics

  • Learn basic Bash. Actually, type

man bash

and at least skim the whole thing; it's pretty easy to follow and not that long. Alternate shells can be nice, but Bash is powerful and always available (learning only zsh, fish, etc., while tempting on your own laptop, restricts you in many situations, such as using existing servers).

Learn at least one text-based editor well. The

nano

editor is one of the simplest for basic editing (opening, editing, saving, searching). However, for the power user in a text terminal, there is no substitute for Vim (

vi

), the hard-to-learn but venerable, fast, and full-featured editor. Many people also use the classic Emacs, particularly for larger editing tasks. (Of course, any modern software developer working on an extensive project is unlikely to use only a pure text-based editor and should also be familiar with modern graphical IDEs and tools.)

Finding documentation:

  • Know how to read official documentation with
    man
    (for the inquisitive,
    man man
    lists the section numbers, e.g. 1 is "regular" commands, 5 is files/conventions, and 8 are for administration). Find man pages with
    apropos
    .
  • Know that some commands are not executables, but Bash builtins, and that you can get help on them with
    help
    and
    help -d
    . You can find out whether a command is an executable, shell builtin or an alias by using
    type command
    .
  • curl cheat.sh/command

    will give a brief "cheat sheet" with common examples of how to use a shell command.

Learn about redirection of output and input using

\>

and

\<

and pipes using

|

. Know

\>

overwrites the output file and

\>\>

appends. Learn about stdout and stderr.

Learn about file glob expansion with

\*

(and perhaps

?

and

[

...

]

) and quoting and the difference between double

"

and single

'

quotes. (See more on variable expansion below.)

Be familiar with Bash job management:

&

, ctrl-z, ctrl-c,

jobs

,

fg

,

bg

,

kill

, etc.

Know

ssh

, and the basics of passwordless authentication, via

ssh-agent

,

ssh-add

, etc.

Basic file management:

ls

and

ls -l

(in particular, learn what every column in

ls -l

means),

less

,

head

,

tail

and

tail -f

(or even better,

less +F

),

ln

and

ln -s

(learn the differences and advantages of hard versus soft links),

chown

,

chmod

,

du

(for a quick summary of disk usage:

du -hs \*

). For filesystem management,

df

,

mount

,

fdisk

,

mkfs

,

lsblk

. Learn what an inode is (

ls -i

or

df -i

).

Basic network management:

ip

or

ifconfig

,

dig

,

traceroute

,

route

.

Learn and use a version control management system, such as

git

.

Know regular expressions well, and the various flags to

grep

/

egrep

. The

-i

,

-o

,

-v

,

-A

,

-B

, and

-C

options are worth knowing.

Learn to use

apt-get

,

yum

,

dnf

or

pacman

(depending on distro) to find and install packages. And make sure you have

pip

to install Python-based command-line tools (a few below are easiest to install via

pip

).

Everyday use

  • In Bash, use Tab to complete arguments or list all available commands and ctrl-r to search through command history (after pressing, type to search, press ctrl-r repeatedly to cycle through more matches, press Enter to execute the found command, or hit the right arrow to put the result in the current line to allow editing).

In Bash, use ctrl-w to delete the last word, and ctrl-u to delete the content from current cursor back to the start of the line. Use alt-b and alt-f to move by word, ctrl-a to move cursor to beginning of line, ctrl-e to move cursor to end of line, ctrl-k to kill to the end of the line, ctrl-l to clear the screen. See

man readline

for all the default keybindings in Bash. There are a lot. For example alt-. cycles through previous arguments, and alt-* expands a glob.

Alternatively, if you love vi-style key-bindings, use

set -o vi

(and

set -o emacs

to put it back).

For editing long commands, after setting your editor (for example

export EDITOR=vim

), ctrl-x ctrl-e will open the current command in an editor for multi-line editing. Or in vi style, escape-v.

To see recent commands, use

history

. Follow with

!n

(where

n

is the command number) to execute again. There are also many abbreviations you can use, the most useful probably being

!$

for last argument and

!!

for last command (see "HISTORY EXPANSION" in the man page). However, these are often easily replaced with ctrl-r and alt-..

Go to your home directory with

cd

. Access files relative to your home directory with the

~

prefix (e.g.

~/.bashrc

). In

sh

scripts refer to the home directory as

$HOME

.

To go back to the previous working directory:

cd -

.

If you are halfway through typing a command but change your mind, hit alt-# to add a

#

at the beginning and enter it as a comment (or use ctrl-a, #, enter). You can then return to it later via command history.

Use

xargs

(or

parallel

). It's very powerful. Note you can control how many items execute per line (

-L

) as well as parallelism (

-P

). If you're not sure if it'll do the right thing, use

xargs echo

first. Also,

-I{}

is handy. Examples:

bash find . -name '\*.py' | xargs grep some\_function cat hosts | xargs -I{} ssh [email protected]{} hostname
  • pstree -p

    is a helpful display of the process tree.

Use

pgrep

and

pkill

to find or signal processes by name (

-f

is helpful).

Know the various signals you can send processes. For example, to suspend a process, use

kill -STOP [pid]

. For the full list, see

man 7 signal
  • Use

nohup

or

disown

if you want a background process to keep running forever.

Check what processes are listening via

netstat -lntp

or

ss -plat

(for TCP; add

-u

for UDP) or

lsof -iTCP -sTCP:LISTEN -P -n

(which also works on macOS).

See also

lsof

and

fuser

for open sockets and files.

See

uptime

or

w

to know how long the system has been running.

Use

alias

to create shortcuts for commonly used commands. For example,

alias ll='ls -latr'

creates a new alias

ll

.

Save aliases, shell settings, and functions you commonly use in

~/.bashrc

, and arrange for login shells to source it. This will make your setup available in all your shell sessions.

Put the settings of environment variables as well as commands that should be executed when you login in

~/.bash\_profile

. Separate configuration will be needed for shells you launch from graphical environment logins and

cron

jobs.

Synchronize your configuration files (e.g.

.bashrc

and

.bash\_profile

) among various computers with Git.

Understand that care is needed when variables and filenames include whitespace. Surround your Bash variables with quotes, e.g.

"$FOO"

. Prefer the

-0

or

-print0

options to enable null characters to delimit filenames, e.g.

locate -0 pattern | xargs -0 ls -al

or

find / -print0 -type d | xargs -0 ls -al

. To iterate on filenames containing whitespace in a for loop, set your IFS to be a newline only using

IFS=$'\n'

.

In Bash scripts, use

set -x

(or the variant

set -v

, which logs raw input, including unexpanded variables and comments) for debugging output. Use strict modes unless you have a good reason not to: Use

set -e

to abort on errors (nonzero exit code). Use

set -u

to detect unset variable usages. Consider

set -o pipefail

too, to abort on errors within pipes (though read up on it more if you do, as this topic is a bit subtle). For more involved scripts, also use

trap

on EXIT or ERR. A useful habit is to start a script like this, which will make it detect and abort on common errors and print a message:

bash set -euo pipefail trap "echo 'error: Script failed: see failed command above'" ERR
  • In Bash scripts, subshells (written with parentheses) are convenient ways to group commands. A common example is to temporarily move to a different working directory, e.g.

bash # do something in current dir (cd /some/other/dir && other-command) # continue in original dir
  • In Bash, note there are lots of kinds of variable expansion. Checking a variable exists:

${name:?error message}

. For example, if a Bash script requires a single argument, just write

input\_file=${1:?usage: $0 input\_file}

. Using a default value if a variable is empty:

${name:-default}

. If you want to have an additional (optional) parameter added to the previous example, you can use something like

output\_file=${2:-logfile}

. If

$2

is omitted and thus empty,

output\_file

will be set to

logfile

. Arithmetic expansion:

i=$(( (i + 1) % 5 ))

. Sequences:

{1..10}

. Trimming of strings:

${var%suffix}

and

${var#prefix}

. For example if

var=foo.pdf

, then

echo ${var%.pdf}.txt

prints

foo.txt

.

Brace expansion using

{

...

}

can reduce having to re-type similar text and automate combinations of items. This is helpful in examples like

mv foo.{txt,pdf} some-dir

(which moves both files),

cp somefile{,.bak}

(which expands to

cp somefile somefile.bak

) or

mkdir -p test-{a,b,c}/subtest-{1,2,3}

(which expands all possible combinations and creates a directory tree). Brace expansion is performed before any other expansion.

The order of expansions is: brace expansion; tilde expansion, parameter and variable expansion, arithmetic expansion, and command substitution (done in a left-to-right fashion); word splitting; and filename expansion. (For example, a range like

{1..20}

cannot be expressed with variables using

{$a..$b}

. Use

seq

or a

for

loop instead, e.g.,

seq $a $b

or

for((i=a; i\<=b; i++)); do ... ; done

.)

The output of a command can be treated like a file via

(known as process substitution). For example, compare local 

/etc/hosts

 with a remote one:

sh diff /etc/hosts

  • When writing scripts you may want to put all of your code in curly braces. If the closing brace is missing, your script will be prevented from executing due to a syntax error. This makes sense when your script is going to be downloaded from the web, since it prevents partially downloaded scripts from executing:

bash { # Your code here }
cat \<<eof input on multiple lines eof></eof>
  • In Bash, redirect both standard output and standard error via:

some-command \>logfile 2\>&1

or

some-command &\>logfile

. Often, to ensure a command does not leave an open file handle to standard input, tying it to the terminal you are in, it is also good practice to add

.
  • Use

man ascii

for a good ASCII table, with hex and decimal values. For general encoding info,

man unicode

,

man utf-8

, and

man latin1

are helpful.

Use

screen

or [

tmux

](https://tmux.github.io/) to multiplex the screen, especially useful on remote ssh sessions and to detach and re-attach to a session.

byobu

can enhance screen or tmux by providing more information and easier management. A more minimal alternative for session persistence only is [

dtach

](https://github.com/bogner/dtach).

In ssh, knowing how to port tunnel with

-L

or

-D

(and occasionally

-R

) is useful, e.g. to access web sites from a remote server.

It can be useful to make a few optimizations to your ssh configuration; for example, this

~/.ssh/config

contains settings to avoid dropped connections in certain network environments, uses compression (which is helpful with scp over low-bandwidth connections), and multiplex channels to the same server with a local control file:

TCPKeepAlive=yes ServerAliveInterval=15 ServerAliveCountMax=6 Compression=yes ControlMaster auto ControlPath /tmp/%[email protected]%h:%p ControlPersist yes
  • A few other options relevant to ssh are security sensitive and should be enabled with care, e.g. per subnet or host or in trusted networks:

StrictHostKeyChecking=no

,

ForwardAgent=yes
  • Consider [

    mosh

    ](https://mosh.mit.edu/) an alternative to ssh that uses UDP, avoiding dropped connections and adding convenience on the road (requires server-side setup).

To get the permissions on a file in octal form, which is useful for system configuration but not available in

ls

and easy to bungle, use something like

sh stat -c '%A %a %n' /etc/timezone

For interaction with files based on the output of another command (like

git

), use

fpp

(PathPicker).

For a simple web server for all files in the current directory (and subdirs), available to anyone on your network, use:

python -m SimpleHTTPServer 7777

(for port 7777 and Python 2) and

python -m http.server 7777

(for port 7777 and Python 3).

For running a command as another user, use

sudo

. Defaults to running as root; use

-u

to specify another user. Use

-i

to login as that user (you will be asked for your password).

For switching the shell to another user, use

su username

or

su - username

. The latter with "-" gets an environment as if another user just logged in. Omitting the username defaults to root. You will be asked for the password of the user you are switching to.

Know about the 128K limit on command lines. This "Argument list too long" error is common when wildcard matching large numbers of files. (When this happens alternatives like

find

and

xargs

may help.)

For a basic calculator (and of course access to Python in general), use the

python

interpreter. For example, ```

2+3 5 ```

Processing files and data

  • To locate a file by name in the current directory,

find . -iname '\*something\*'

(or similar). To find a file anywhere by name, use

locate something

(but bear in mind

updatedb

may not have indexed recently created files).

For general searching through source or data files, there are several options more advanced or faster than

grep -r

, including (in rough order from older to newer) [

ack

](https://github.com/beyondgrep/ack2), [

ag

](https://github.com/ggreer/the_silver_searcher) ("the silver searcher"), and [

rg

](https://github.com/BurntSushi/ripgrep) (ripgrep).

To convert HTML to text:

lynx -dump -stdin
  • For Markdown, HTML, and all kinds of document conversion, try [

    pandoc

    ](http://pandoc.org/). For example, to convert a Markdown document to Word format:

pandoc README.md --from markdown --to docx -o temp.docx
  • If you must handle XML,

xmlstarlet

is old but good.

For Excel or CSV files, csvkit provides

in2csv

,

csvcut

,

csvjoin

,

csvgrep

, etc.

Know about

sort

and

uniq

, including uniq's

-u

and

-d

options -- see one-liners below. See also

comm

.

Know about

cut

,

paste

, and

join

to manipulate text files. Many people use

cut

but forget about

join

.

Know about

wc

to count newlines (

-l

), characters (

-m

), words (

-w

) and bytes (

-c

).

Know about

tee

to copy from stdin to a file and also to stdout, as in

ls -al | tee file.txt

.

Know that locale affects a lot of command line tools in subtle ways, including sorting order (collation) and performance. Most Linux installations will set

LANG

or other locale variables to a local setting like US English. But be aware sorting will change if you change locale. And know i18n routines can make sort or other commands run many times slower. In some situations (such as the set operations or uniqueness operations below) you can safely ignore slow i18n routines entirely and use traditional byte-based sort order, using

export LC\_ALL=C

.

You can set a specific command's environment by prefixing its invocation with the environment variable settings, as in

TZ=Pacific/Fiji date

.

Know basic

awk

and

sed

for simple data munging. See One-liners for examples.

To replace all occurrences of a string in place, in one or more files:

sh perl -pi.bak -e 's/old-string/new-string/g' my-files-\*.txt
rename

command also allows multiple renames, but be careful as its functionality is not the same on all Linux distributions.)

sh # Full rename of filenames, directories, and contents foo -\> bar: repren --full --preserve-case --from foo --to bar . # Recover backup files whatever.bak -\> whatever: repren --renames --from '(.\*)\.bak' --to '\1' \*.bak # Same as above, using rename, if available: rename 's/\.bak$//' \*.bak
  • As the man page says,

rsync

really is a fast and extraordinarily versatile file copying tool. It's known for synchronizing between machines but is equally useful locally. When security restrictions allow, using

rsync

instead of

scp

allows recovery of a transfer without restarting from scratch. It also is among the fastest ways to delete large numbers of files:

sh mkdir empty && rsync -r --delete empty/ some-dir && rmdir some-dir
rsync --progress

, or, for block-level copying,

dd status=progress

.

Use

shuf

to shuffle or select random lines from a file.

Know

sort

's options. For numbers, use

-n

, or

-h

for handling human-readable numbers (e.g. from

du -h

). Know how keys work (

-t

and

-k

). In particular, watch out that you need to write

-k1,1

to sort by only the first field;

-k1

means sort according to the whole line. Stable sort (

sort -s

) can be useful. For example, to sort first by field 2, then secondarily by field 1, you can use

sort -k1,1 | sort -s -k2,2

.

If you ever need to write a tab literal in a command line in Bash (e.g. for the -t argument to sort), press ctrl-v [Tab] or write

$'\t'

(the latter is better as you can copy/paste it).

The standard tools for patching source code are

diff

and

patch

. See also

diffstat

for summary statistics of a diff and

sdiff

for a side-by-side diff. Note

diff -r

works for entire directories. Use

diff -r tree1 tree2 | diffstat

for a summary of changes. Use

vimdiff

to compare and edit files.

For binary files, use

hd

,

hexdump

or

xxd

for simple hex dumps and

bvi

,

hexedit

or

biew

for binary editing.

Also for binary files,

strings

(plus

grep

, etc.) lets you find bits of text.

For binary diffs (delta compression), use

xdelta3

.

To convert text encodings, try

iconv

. Or

uconv

for more advanced use; it supports some advanced Unicode things. For example:

sh # Displays hex codes or actual names of characters (useful for debugging): uconv -f utf-8 -t utf-8 -x '::Any-Hex;' \< input.txt uconv -f utf-8 -t utf-8 -x '::Any-Name;' \< input.txt # Lowercase and removes all accents (by expanding and dropping them): uconv -f utf-8 -t utf-8 -x '::Any-Lower; ::Any-NFD; [:Nonspacing Mark:] \>; ::Any-NFC;' \< input.txt \> output.txt
  • To split files into pieces, see

split

(to split by size) and

csplit

(to split by a pattern).

Date and time: To get the current date and time in the helpful ISO 8601 format, use

date -u +"%Y-%m-%dT%H:%M:%SZ"

(other options are problematic). To manipulate date and time expressions, use

dateadd

,

datediff

,

strptime

etc. from [

dateutils

](http://www.fresse.org/dateutils/).

Use

zless

,

zmore

,

zcat

, and

zgrep

to operate on compressed files.

File attributes are settable via

chattr

and offer a lower-level alternative to file permissions. For example, to protect against accidental file deletion the immutable flag:

sudo chattr +i /critical/directory/or/file
  • Use

getfacl

and

setfacl

to save and restore file permissions. For example:

sh getfacl -R /some/path \> permissions.txt setfacl --restore=permissions.txt
  • To create empty files quickly, use

truncate

(creates sparse file),

fallocate

(ext4, xfs, btrfs and ocfs2 filesystems),

xfs\_mkfile

(almost any filesystems, comes in xfsprogs package),

mkfile

(for Unix-like systems like Solaris, Mac OS).

System debugging

  • For web debugging,

curl

and

curl -I

are handy, or their

wget

equivalents, or the more modern [

httpie

](https://github.com/jkbrzt/httpie).

To know current cpu/disk status, the classic tools are

top

(or the better

htop

),

iostat

, and

iotop

. Use

iostat -mxz 15

for basic CPU and detailed per-partition disk stats and performance insight.

For network connection details, use

netstat

and

ss

.

For a quick overview of what's happening on a system,

dstat

is especially useful. For broadest overview with details, use [

glances

](https://github.com/nicolargo/glances).

To know memory status, run and understand the output of

free

and

vmstat

. In particular, be aware the "cached" value is memory held by the Linux kernel as file cache, so effectively counts toward the "free" value.

Java system debugging is a different kettle of fish, but a simple trick on Oracle's and some other JVMs is that you can run

kill -3 <pid></pid>

and a full stack trace and heap summary (including generational garbage collection details, which can be highly informative) will be dumped to stderr/logs. The JDK's

jps

,

jstat

,

jstack

,

jmap

are useful. SJK tools are more advanced.

For looking at why a disk is full, [

ncdu

](https://dev.yorhel.nl/ncdu) saves time over the usual commands like

du -sh \*

.

The

ab

tool (comes with Apache) is helpful for quick-and-dirty checking of web server performance. For more complex load testing, try

siege

.

Know about

strace

and

ltrace

. These can be helpful if a program is failing, hanging, or crashing, and you don't know why, or if you want to get a general idea of performance. Note the profiling option (

-c

), and the ability to attach to a running process (

-p

). Use trace child option (

-f

) to avoid missing important calls.

Know about

ldd

to check shared libraries etc — but never run it on untrusted files.

Know how to connect to a running process with

gdb

and get its stack traces.

Use

/proc

. It's amazingly helpful sometimes when debugging live problems. Examples:

/proc/cpuinfo

,

/proc/meminfo

,

/proc/cmdline

,

/proc/xxx/cwd

,

/proc/xxx/exe

,

/proc/xxx/fd/

,

/proc/xxx/smaps

(where

xxx

is the process id or pid).

For deeper systems and performance analyses, look at

stap

(SystemTap), [

perf

](https://en.wikipedia.org/wiki/Perf_%28Linux%29), and [

sysdig

](https://github.com/draios/sysdig).

Check what OS you're on with

uname

or

uname -a

(general Unix/kernel info) or

lsb\_release -a

(Linux distro info).

Use

dmesg

whenever something's acting really funny (it could be hardware or driver issues).

If you delete a file and it doesn't free up expected disk space as reported by

du

, check whether the file is in use by a process:

lsof | grep deleted | grep "filename-of-my-big-file"

One-liners

A few examples of piecing together commands:

  • It is remarkably helpful sometimes that you can do set intersection, union, and difference of text files via

sort

/

uniq

. Suppose

a

and

b

are text files that are already uniqued. This is fast, and works on files of arbitrary size, up to many gigabytes. (Sort is not limited by memory, though you may need to use the

-T

option if

/tmp

is on a small root partition.) See also the note about

LC\_ALL

above and

sort

's

-u

option (left out for clarity below).

sh sort a b | uniq \> c # c is a union b sort a b | uniq -d \> c # c is a intersect b sort a b b | uniq -u \> c # c is set difference a - b
  • Pretty-print two JSON files, normalizing their syntax, then coloring and paginating the result:

diff
  • Use

grep . \*

to quickly examine the contents of all files in a directory (so each line is paired with the filename), or

head -100 \*

(so each file has a heading). This can be useful for directories filled with config settings like those in

/sys

,

/proc

,

/etc

.

Summing all numbers in the third column of a text file (this is probably 3X faster and 3X less code than equivalent Python):

sh awk '{ x += $3 } END { print x }' myfile
  • To see sizes/dates on a tree of files, this is like a recursive

ls -l

but is easier to read than

ls -lR

:

sh find . -type f -ls
  • Say you have a text file, like a web server log, and a certain value that appears on some lines, such as an

acct\_id

parameter that is present in the URL. If you want a tally of how many requests for each

acct\_id

:

sh egrep -o 'acct\_id=[0-9]+' access.log | cut -d= -f2 | sort | uniq -c | sort -rn
  • To continuously monitor changes, use

watch

, e.g. check changes to files in a directory with

watch -d -n 2 'ls -rtlh | tail'

or to network settings while troubleshooting your wifi settings with

watch -d -n 2 ifconfig

.

Run this function to get a random tip from this document (parses Markdown and extracts an item):

sh function taocl() { curl -s https://raw.githubusercontent.com/jlevy/the-art-of-command-line/master/README.md | sed '/cowsay[.]png/d' | pandoc -f markdown -t html | xmlstarlet fo --html --dropdtd | xmlstarlet sel -t -v "(html/body/ul/li[count(p)\>0])[$RANDOM mod last()+1]" | xmlstarlet unesc | fmt -80 | iconv -t US }

Obscure but useful

  • expr

    : perform arithmetic or boolean operations or evaluate regular expressions

m4

: simple macro processor

yes

: print a string a lot

cal

: nice calendar

env

: run a command (useful in scripts)

printenv

: print out environment variables (useful in debugging and scripts)

look

: find English words (or lines in a file) beginning with a string

cut

,

paste

and

join

: data manipulation

fmt

: format text paragraphs

pr

: format text into pages/columns

fold

: wrap lines of text

column

: format text fields into aligned, fixed-width columns or tables

expand

and

unexpand

: convert between tabs and spaces

nl

: add line numbers

seq

: print numbers

bc

: calculator

factor

: factor integers

toe

: table of terminfo entries

nc

: network debugging and data transfer

socat

: socket relay and tcp port forwarder (similar to

netcat

)

dd

: moving data between files or devices

file

: identify type of a file

tree

: display directories and subdirectories as a nesting tree; like

ls

but recursive

stat

: file info

time

: execute and time a command

timeout

: execute a command for specified amount of time and stop the process when the specified amount of time completes.

lockfile

: create semaphore file that can only be removed by

rm -f
  • logrotate

    : rotate, compress and mail logs.

watch

: run a command repeatedly, showing results and/or highlighting changes

[

when-changed

](https://github.com/joh/when-changed): runs any command you specify whenever it sees file changed. See

inotifywait

and

entr

as well.

tac

: print files in reverse

comm

: compare sorted files line by line

strings

: extract text from binary files

tr

: character translation or manipulation

iconv

or

uconv

: conversion for text encodings

split

and

csplit

: splitting files

sponge

: read all input before writing it, useful for reading from then writing to the same file, e.g.,

grep -v something some-file | sponge some-file
  • units

    : unit conversions and calculations; converts furlongs per fortnight to twips per blink (see also

    /usr/share/units/definitions.units

    )

apg

: generates random passwords

xz

: high-ratio file compression

ldd

: dynamic library info

nm

: symbols from object files

ab

or [

wrk

](https://github.com/wg/wrk): benchmarking web servers

strace

: system call debugging

cssh

: visual concurrent shell

rsync

: sync files and folders over SSH or in local file system

host

and

dig

: DNS lookups

lsof

: process file descriptor and socket info

dstat

: useful system stats

iostat

: Disk usage stats

mpstat

: CPU usage stats

vmstat

: Memory usage stats

htop

: improved version of top

last

: login history

w

: who's logged on

id

: user/group identity info

ss

: socket statistics

dmesg

: boot and system error messages

sysctl

: view and configure Linux kernel parameters at run time

hdparm

: SATA/ATA disk manipulation/performance

lsblk

: list block devices: a tree view of your disks and disk partitions

lshw

,

lscpu

,

lspci

,

lsusb

,

dmidecode

: hardware information, including CPU, BIOS, RAID, graphics, devices, etc.

lsmod

and

modinfo

: List and show details of kernel modules.

fortune

,

ddate

, and

sl

: um, well, it depends on whether you consider steam locomotives and Zippy quotations "useful"

macOS only

These are items relevant only on macOS.

  • Package management with

brew

(Homebrew) and/or

port

(MacPorts). These can be used to install on macOS many of the above commands.

Copy output of any command to a desktop app with

pbcopy

and paste input from one with

pbpaste

.

  • To enable the Option key in macOS Terminal as an alt key (such as used in the commands above like alt-b, alt-f, etc.), open Preferences -> Profiles -> Keyboard and select "Use Option as Meta key".

To open a file with a desktop app, use

open

or

open -a /Applications/Whatever.app

.

Spotlight: Search files with

mdfind

and list metadata (such as photo EXIF info) with

mdls

.

Be aware macOS is based on BSD Unix, and many commands (for example

ps

,

ls

,

tail

,

awk

,

sed

) have many subtle variations from Linux, which is largely influenced by System V-style Unix and GNU tools. You can often tell the difference by noting a man page has the heading "BSD General Commands Manual." In some cases GNU versions can be installed, too (such as

gawk

and

gsed

for GNU awk and sed). If writing cross-platform Bash scripts, avoid such commands (for example, consider Python or

perl

) or test carefully.

To get macOS release information, use

sw\_vers

.

Windows only

These items are relevant only on Windows.

Ways to obtain Unix tools under Windows

  • Access the power of the Unix shell under Microsoft Windows by installing Cygwin. Most of the things described in this document will work out of the box.

  • On Windows 10, you can use Windows Subsystem for Linux (WSL), which provides a familiar Bash environment with Unix command line utilities.

  • If you mainly want to use GNU developer tools (such as GCC) on Windows, consider MinGW and its MSYS package, which provides utilities such as bash, gawk, make and grep. MSYS doesn't have all the features compared to Cygwin. MinGW is particularly useful for creating native Windows ports of Unix tools.

  • Another option to get Unix look and feel under Windows is Cash. Note that only very few Unix commands and command-line options are available in this environment.

Useful Windows command-line tools

  • You can perform and script most Windows system administration tasks from the command line by learning and using

wmic

.

Native command-line Windows networking tools you may find useful include

ping

,

ipconfig

,

tracert

, and

netstat

.

You can perform many useful Windows tasks by invoking the

Rundll32

command.

Cygwin tips and tricks

  • Install additional Unix programs with the Cygwin's package manager.

Use

mintty

as your command-line window.

Access the Windows clipboard through

/dev/clipboard

.

Run

cygstart

to open an arbitrary file through its registered application.

Access the Windows registry with

regtool

.

Note that a

C:\

Windows drive path becomes

/cygdrive/c

under Cygwin, and that Cygwin's

/

appears under

C:\cygwin

on Windows. Convert between Cygwin and Windows-style file paths with

cygpath

. This is most useful in scripts that invoke Windows programs.

More resources

Disclaimer

With the exception of very small tasks, code is written so others can read it. With power comes responsibility. The fact you can do something in Bash doesn't necessarily mean you should! ;)

License

Creative Commons License

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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