Repository files navigation

🌍Čeština ∙Deutsch ∙Ελληνικά ∙English ∙Español ∙Français ∙Indonesia ∙Italiano ∙日本語 ∙한국어 ∙polski ∙Português ∙Română ∙Русский ∙Slovenščina ∙Українська ∙简体中文 ∙繁體中文

Note: I'm planning to revise this and looking for a new co-author to help with expanding this into a more comprehensive guide. While it's very popular, it could be broader and a bit deeper. 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. Thank you!

• Meta
• Basics
• Everyday use
• Processing files and data
• System debugging
• One-liners
• Obscure but useful
• macOS only
• Windows only
• More resources
• Disclaimer

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 ofmany authors and translators.Some of thisoriginallyappearedonQuora,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!

Scope:

• This guide is for both beginners and experienced users. The goals arebreadth (everything important),specificity (give concrete examples of the most common case), andbrevity (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. Useapt,yum,dnf,pacman,pip orbrew (as appropriate) to install new programs.
• UseExplainshell to get a helpful breakdown of what commands, options, pipes etc. do.

• Learn basic Bash. Actually, typeman 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 (learningonly 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. Thenano 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 withman (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 withapropos.
  • Know that some commands are not executables, but Bash builtins, and that you can get help on them withhelp andhelp -d. You can find out whether a command is an executable, shell builtin or an alias by usingtype 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.

• Knowssh, and the basics of passwordless authentication, viassh-agent,ssh-add, etc.

• Basic file management:ls andls -l (in particular, learn what every column inls -l means),less,head,tail andtail -f (or even better,less +F),ln andln -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 ordf -i).

• Basic network management:ip orifconfig,dig,traceroute,route.

• Learn and use a version control management system, such asgit.

• Know regular expressions well, and the various flags togrep/egrep. The-i,-o,-v,-A,-B, and-C options are worth knowing.

• Learn to useapt-get,yum,dnf orpacman (depending on distro) to find and install packages. And make sure you havepip to install Python-based command-line tools (a few below are easiest to install viapip).

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

• In Bash, usectrl-w to delete the last word, andctrl-u to delete the content from current cursor back to the start of the line. Usealt-b andalt-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. Seeman readline for all the default keybindings in Bash. There are a lot. For examplealt-. cycles through previous arguments, andalt-* expands a glob.

• Alternatively, if you love vi-style key-bindings, useset -o vi (andset -o emacs to put it back).

• For editing long commands, after setting your editor (for exampleexport EDITOR=vim),ctrl-xctrl-e will open the current command in an editor for multi-line editing. Or in vi style,escape-v.

• To see recent commands, usehistory. Follow with!n (wheren 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 withctrl-r andalt-..

• Go to your home directory withcd. Access files relative to your home directory with the~ prefix (e.g.~/.bashrc). Insh 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, hitalt-# to add a# at the beginning and enter it as a comment (or usectrl-a,#,enter). You can then return to it later via command history.

• Usexargs (orparallel). 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, usexargs echo first. Also,-I{} is handy. Examples:

      find. -name'*.py'| xargs grep some_function      cat hosts| xargs -I{} ssh root@{} hostname

• pstree -p is a helpful display of the process tree.

• Usepgrep andpkill to find or signal processes by name (-f is helpful).

• Know the various signals you can send processes. For example, to suspend a process, usekill -STOP [pid]. For the full list, seeman 7 signal

• Usenohup ordisown if you want a background process to keep running forever.

• Check what processes are listening vianetstat -lntp orss -plat (for TCP; add-u for UDP) orlsof -iTCP -sTCP:LISTEN -P -n (which also works on macOS).

• See alsolsof andfuser for open sockets and files.

• Seeuptime orw to know how long the system has been running.

• Usealias to create shortcuts for commonly used commands. For example,alias ll='ls -latr' creates a new aliasll.

• Save aliases, shell settings, and functions you commonly use in~/.bashrc, andarrange 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 andcron 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."$FOO". Prefer the-0 or-print0 options to enable null characters to delimit filenames, e.g.locate -0 pattern | xargs -0 ls -al orfind / -print0 -type d | xargs -0 ls -al. To iterate on filenames containing whitespace in a for loop, set your IFS to be a newline only usingIFS=$'\n'.

• In Bash scripts, useset -x (or the variantset -v, which logs raw input, including unexpanded variables and comments) for debugging output. Use strict modes unless you have a good reason not to: Useset -e to abort on errors (nonzero exit code). Useset -u to detect unset variable usages. Considerset -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 usetrap 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:

set -euo pipefailtrap"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.

# 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:${name:?error message}. For example, if a Bash script requires a single argument, just writeinput_file=${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 likeoutput_file=${2:-logfile}. If$2 is omitted and thus empty,output_file will be set tologfile. Arithmetic expansion:i=$(( (i + 1) % 5 )). Sequences:{1..10}. Trimming of strings:${var%suffix} and${var#prefix}. For example ifvar=foo.pdf, thenecho ${var%.pdf}.txt printsfoo.txt.

• Brace expansion using{...} can reduce having to re-type similar text and automate combinations of items. This is helpful in examples likemv foo.{txt,pdf} some-dir (which moves both files),cp somefile{,.bak} (which expands tocp somefile somefile.bak) ormkdir -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}. Useseq or afor loop instead, e.g.,seq $a $b orfor((i=a; i<=b; i++)); do ... ; done.)

• The output of a command can be treated like a file via<(some command) (known as process substitution). For example, compare local/etc/hosts with a remote one:

      diff /etc/hosts<(ssh somehost cat /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:

{# Your code here}

• A "here document" allowsredirection of multiple lines of input as if from a file:

cat <<EOFinputon multiple linesEOF

• In Bash, redirect both standard output and standard error via:some-command >logfile 2>&1 orsome-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</dev/null.

• Useman ascii for a good ASCII table, with hex and decimal values. For general encoding info,man unicode,man utf-8, andman latin1 are helpful.

• Usescreen ortmux 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 isdtach.

• 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/%r@%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

• Considermosh 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 inls and easy to bungle, use something like

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

• For interactive selection of values from the output of another command, usepercol orfzf.

• For interaction with files based on the output of another command (likegit), usefpp (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) andpython -m http.server 7777 (for port 7777 and Python 3).

• For running a command as another user, usesudo. Defaults to running as root; use-u to specify another user. Use-i to login as that user (you will be asked foryour password).

• For switching the shell to another user, usesu username orsu - 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 passwordof the user you are switching to.

• Know about the128K limit on command lines. This "Argument list too long" error is common when wildcard matching large numbers of files. (When this happens alternatives likefind andxargs may help.)

• For a basic calculator (and of course access to Python in general), use thepython interpreter. For example,

>>> 2+35

• To locate a file by name in the current directory,find . -iname '*something*' (or similar). To find a file anywhere by name, uselocate something (but bear in mindupdatedb may not have indexed recently created files).

• For general searching through source or data files, there are several options more advanced or faster thangrep -r, including (in rough order from older to newer)ack,ag ("the silver searcher"), andrg (ripgrep).

• To convert HTML to text:lynx -dump -stdin

• For Markdown, HTML, and all kinds of document conversion, trypandoc. 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 JSON, usejq. For interactive use, also seejid andjiq.

• For YAML, useshyaml.

• For Excel or CSV files,csvkit providesin2csv,csvcut,csvjoin,csvgrep, etc.

• For Amazon S3,s3cmd is convenient ands4cmd is faster. Amazon'saws and the improvedsaws are essential for other AWS-related tasks.

• Know aboutsort anduniq, including uniq's-u and-d options -- see one-liners below. See alsocomm.

• Know aboutcut,paste, andjoin to manipulate text files. Many people usecut but forget aboutjoin.

• Know aboutwc to count newlines (-l), characters (-m), words (-w) and bytes (-c).

• Know abouttee to copy from stdin to a file and also to stdout, as inls -al | tee file.txt.

• For more complex calculations, including grouping, reversing fields, and statistical calculations, considerdatamash.

• Know that locale affects a lot of command line tools in subtle ways, including sorting order (collation) and performance. Most Linux installations will setLANG 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 runmany 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, usingexport LC_ALL=C.

• You can set a specific command's environment by prefixing its invocation with the environment variable settings, as inTZ=Pacific/Fiji date.

• Know basicawk andsed for simple data munging. SeeOne-liners for examples.

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

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

• To rename multiple files and/or search and replace within files, tryrepren. (In some cases therename command also allows multiple renames, but be careful as its functionality is not the same on all Linux distributions.)

# 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, usingrsync instead ofscp allows recovery of a transfer without restarting from scratch. It also is among thefastest ways to delete large numbers of files:

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

• For monitoring progress when processing files, usepv,pycp,pmonitor,progress,rsync --progress, or, for block-level copying,dd status=progress.

• Useshuf to shuffle or select random lines from a file.

• Knowsort's options. For numbers, use-n, or-h for handling human-readable numbers (e.g. fromdu -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 usesort -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), pressctrl-v[Tab] or write$'\t' (the latter is better as you can copy/paste it).

• The standard tools for patching source code arediff andpatch. See alsodiffstat for summary statistics of a diff andsdiff for a side-by-side diff. Notediff -r works for entire directories. Usediff -r tree1 tree2 | diffstat for a summary of changes. Usevimdiff to compare and edit files.

• For binary files, usehd,hexdump orxxd for simple hex dumps andbvi,hexedit orbiew for binary editing.

• Also for binary files,strings (plusgrep, etc.) lets you find bits of text.

• For binary diffs (delta compression), usexdelta3.

• To convert text encodings, tryiconv. Oruconv for more advanced use; it supports some advanced Unicode things. For example:

# 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, seesplit (to split by size) andcsplit (to split by a pattern).

• Date and time: To get the current date and time in the helpfulISO 8601 format, usedate -u +"%Y-%m-%dT%H:%M:%SZ" (other optionsareproblematic). To manipulate date and time expressions, usedateadd,datediff,strptime etc. fromdateutils.

• Usezless,zmore,zcat, andzgrep to operate on compressed files.

• File attributes are settable viachattr 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

• Usegetfacl andsetfacl to save and restore file permissions. For example:

   getfacl -R /some/path> permissions.txt   setfacl --restore=permissions.txt

• To create empty files quickly, usetruncate (createssparse 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).

• For web debugging,curl andcurl -I are handy, or theirwget equivalents, or the more modernhttpie.

• To know current cpu/disk status, the classic tools aretop (or the betterhtop),iostat, andiotop. Useiostat -mxz 15 for basic CPU and detailed per-partition disk stats and performance insight.

• For network connection details, usenetstat andss.

• For a quick overview of what's happening on a system,dstat is especially useful. For broadest overview with details, useglances.

• To know memory status, run and understand the output offree andvmstat. 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 runkill -3 <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'sjps,jstat,jstack,jmap are useful.SJK tools are more advanced.

• Usemtr as a better traceroute, to identify network issues.

• For looking at why a disk is full,ncdu saves time over the usual commands likedu -sh *.

• To find which socket or process is using bandwidth, tryiftop ornethogs.

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

• For more serious network debugging,wireshark,tshark, orngrep.

• Know aboutstrace andltrace. 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 aboutldd to check shared libraries etc — butnever run it on untrusted files.

• Know how to connect to a running process withgdb 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 (wherexxx is the process id or pid).

• When debugging why something went wrong in the past,sar can be very helpful. It shows historic statistics on CPU, memory, network, etc.

• For deeper systems and performance analyses, look atstap (SystemTap),perf, andsysdig.

• Check what OS you're on withuname oruname -a (general Unix/kernel info) orlsb_release -a (Linux distro info).

• Usedmesg 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 bydu, check whether the file is in use by a process:lsof | grep deleted | grep "filename-of-my-big-file"

A few examples of piecing together commands:

• It is remarkably helpful sometimes that you can do set intersection, union, and difference of text files viasort/uniq. Supposea andb 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 aboutLC_ALL above andsort's-u option (left out for clarity below).

      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 <(jq --sort-keys . < file1.json) <(jq --sort-keys . < file2.json) | colordiff | less -R

• Usegrep . * to quickly examine the contents of all files in a directory (so each line is paired with the filename), orhead -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):

      awk'{ x += $3 } END { print x }' myfile

• To see sizes/dates on a tree of files, this is like a recursivels -l but is easier to read thanls -lR:

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

      egrep -o'acct_id=[0-9]+' access.log| cut -d= -f2| sort| uniq -c| sort -rn

• To continuously monitor changes, usewatch, e.g. check changes to files in a directory withwatch -d -n 2 'ls -rtlh | tail' or to network settings while troubleshooting your wifi settings withwatch -d -n 2 ifconfig.

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

functiontaocl() {        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      }

• 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 andjoin: 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 andunexpand: convert between tabs and spaces

• nl: add line numbers

• seq: print numbers

• bc: calculator

• factor: factor integers

• gpg: encrypt and sign files

• toe: table of terminfo entries

• nc: network debugging and data transfer

• socat: socket relay and tcp port forwarder (similar tonetcat)

• slurm: network traffic visualization

• dd: moving data between files or devices

• file: identify type of a file

• tree: display directories and subdirectories as a nesting tree; likels 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 byrm -f

• logrotate: rotate, compress and mail logs.

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

• when-changed: runs any command you specify whenever it sees file changed. Seeinotifywait andentr 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 oruconv: conversion for text encodings

• split andcsplit: 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 orwrk: benchmarking web servers

• strace: system call debugging

• mtr: better traceroute for network debugging

• cssh: visual concurrent shell

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

• wireshark andtshark: packet capture and network debugging

• ngrep: grep for the network layer

• host anddig: DNS lookups

• lsof: process file descriptor and socket info

• dstat: useful system stats

• glances: high level, multi-subsystem overview

• 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

• sar: historic system stats

• iftop ornethogs: network utilization by socket or process

• 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 andmodinfo: List and show details of kernel modules.

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

These are items relevantonly on macOS.

• Package management withbrew (Homebrew) and/orport (MacPorts). These can be used to install on macOS many of the above commands.

• Copy output of any command to a desktop app withpbcopy and paste input from one withpbpaste.

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

• To open a file with a desktop app, useopen oropen -a /Applications/Whatever.app.

• Spotlight: Search files withmdfind and list metadata (such as photo EXIF info) withmdls.

• Be aware macOS is based on BSD Unix, and many commands (for exampleps,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 asgawk andgsed for GNU awk and sed). If writing cross-platform Bash scripts, avoid such commands (for example, consider Python orperl) or test carefully.

• To get macOS release information, usesw_vers.

These items are relevantonly on Windows.

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

• On Windows 10, you can useWindows 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, considerMinGW and itsMSYS 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 isCash. Note that only very few Unix commands and command-line options are available in this environment.

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

• Native command-line Windows networking tools you may find useful includeping,ipconfig,tracert, andnetstat.

• You can performmany useful Windows tasks by invoking theRundll32 command.

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

• Usemintty as your command-line window.

• Access the Windows clipboard through/dev/clipboard.

• Runcygstart to open an arbitrary file through its registered application.

• Access the Windows registry withregtool.

• Note that aC:\ Windows drive path becomes/cygdrive/c under Cygwin, and that Cygwin's/ appears underC:\cygwin on Windows. Convert between Cygwin and Windows-style file paths withcygpath. This is most useful in scripts that invoke Windows programs.

• awesome-shell: A curated list of shell tools and resources.
• awesome-osx-command-line: A more in-depth guide for the macOS command line.
• Strict mode for writing better shell scripts.
• shellcheck: A shell script static analysis tool. Essentially, lint for bash/sh/zsh.
• Filenames and Pathnames in Shell: The sadly complex minutiae on how to handle filenames correctly in shell scripts.
• Data Science at the Command Line: More commands and tools helpful for doing data science, from the book of the same name

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

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