Commands

Guides> linux > commands

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Introduction

This page enumerates, categorizes, and very briefly describes a bunch of Linux command-line programs that you may find useful. The documentation provided here is (intentionally) insufficient to actually use them; recall that you can use the man command to read the online manual page (arrow keys and pgup/pgdn scroll, 'q' to exit). Therefore, to read about all the options accepted by the ls program, run

$ man ls

Some of the programs below are standard, as part of the "coreutils" and "util-linux" packages in Arch Linux; others will need to be installed separately.

Vocabulary

Only one right now.

• Recursive refers to an operation that descends into child directories,

their children, their children's children, and so forth. Therefore,

applying the '-r' parameter to grep will cause it to search not only the

files in the current directory, but also all files within and below it.

Commands

The single most important one

• man: access the online manual

The second most important one, for system administration

• sudo: run a program with temporarily-increased privileges

Get me outta here

• exit: terminate the terminal session
• logout: terminate the terminal session
• Ctrl-d: terminate the terminal session (only when no other characters have

been entered at the prompt; otherwise behaves as Enter)

Basic filesystem stuff

• pwd: report the current working directory
• ls: list information about files
• cd: change to a different directory
• mkdir: create a directory
• mv: move a file (equivalent to renaming it, even if its new name puts it

in a new directory)

• cp: copy a file
• rm: remove a file
• rmdir: remove a directory
• touch: create a file or, if the file exists, update its modification

time

• chmod: change permissions of a file
• chown: change ownership (user/group) of a file
• ln: create a (symbolic) link

Text analysis

• grep: search inside file(s)
• wc: count characters/words/lines in a file
• echo: output a string to the terminal
• cat: output the contents of a file to the terminal
• head: print lines from the beginning of a file
• tail: print lines from the end of a file
• diff: compare the contents of files
• less: allow keyboard-based scrolling through a file (manpages are run

through less, thus the same navigation commands apply)

Text manipulation

• sort: you'll never guess
• uniq: filter out consecutive duplicate lines from a file
• cut: combine files line by line
• paste: separate files line by line
• sed: modify files, line by line, according to regular expressions
• awk: lightweight programming language for modifying files line by line
• fold: break long lines into paragraphs
• fmt: more complex version of fold
• column: neatly format text into evenly-spaced columns

More complex file stuff

• find: locate files based on metadata (eg, name, size, modification time)
• xargs: often used to send the results of find to other programs
• tar: create an archive containing multiple files
• gzip: compress a file (historically ubiquitous)
• xz: compress a file (more recently popular)
• stat: report metadata information about a file
• dd: copy file contents (more tweakable than cp, useful for copying from

raw devices, eg, /dev/urandom)

Measuring and monitoring

• du: measure sizes of files/directories
• time: measure the runtime of a program
• ps: list running processes (instant snapshot)
• top: list running processes (updates repeatedly)

Random

• date: report the date
• sleep: pause for a configurable duration
• history: list recently-run commands
• clear: clear the terminal screen
• reset: clear the terminal screen with extreme prejudice (useful if you want to

erase the scrollback buffer or reverse text corruption when playing with, eg, customized fonts/colors in your shell)

Network

• ifconfig: report information about network interface configuration

(classic tool)

• ip: report information about network interface configuration (newer tool)
• route: manipulate routing table
• netstat: report information about network configuration
• ping: check reachability of machines over the Internet
• traceroute: trace the route to another machine on the Internet
• mtr: trace the route to another machine on the Internet (my preferred choice)
• netcat: the Swiss Army Knife of the Internet
• wget: save web pages as files
• curl: save web pages as files (alternate)

More complex

• ssh: log into a machine over the Internet
• rsync: efficiently copies files (even across the Internet)
• tmux: resumable terminal sessions
• script: record the results of a terminal session in a file
• cron: schedule programs to be run at certain times
• bc: do math