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