Linux Tutorial by Example: Most Frequently Used Shell Commands

, 2012-09-13, …, 2014-01-09

This is a list of most frequently used unix/linux commands. Each is used multiple times per day. To work in Linux efficiently, you should memorize by reflex every command on this page.

The code here are based on Ubuntu Linux, but 99% of them work in any unix, including Mac OS X. (except a few that are specific to Linux or distro.)

File/Directory Manipulation

code	purpose
`ls`	list files in current directory
`ls -al`	list all files in current dir, including dot files
`ls -al \| grep string`	show file name matching `string`
`cd dirpath`	change directory
`cd`	go to `$HOME` dir
`pwd`	show the current dir

You can set bash to show current dir path and time in your prompt. 〔☛ Linux: Bash Shell Prompt Color ＆ Timestamp〕

code	purpose
`touch filename`	create a new file, or update timestamp of the file if it exists already.
`rm filename`	delete a file
`rm -r dirname`	delete a dir
`cp filename new filename`	copy a file
`cp -r dirname new name`	copy a dir
`mkdir new dir name`	create a new dir
`rmdir dirname`	delete a dir only if it is empty
`mv filename new name`	rename file, or move to a diff dir.
`du -sh dirname`	show dir size. 〔☛ Linux: Show Directory Size: du〕

Emacs's dired lets you do these much easier. 〔☛ Emacs: File Management (dired tutorial)〕 But you have to learn emacs first. 〔☛ Xah Emacs Tutorial〕

Also, tree is a nice command for getting sense of dir structure. 〔☛ Linux: View Directory as Tree〕

Viewing Files

code	purpose
`cat fname`	view a file
`cat fname \| more`	view a file by page. Type 【`q`】 to exit. Type 【`h`】 for other keys. `more` can also be `less`; the latter is better.
`vi fname`	view a file. Type 【`Esc` `:` `q`】 to exit. 〔☛ Emergency vi (vi tutorial)〕
`head fname`	view the first few lines of a (big) file. (to get a idea what the heck the file contains)
`tail fname`	view the last few lines of a file.
`tail -f fname`	view the last few lines of a growing file, updated continuously. Typically used on log files.
`file fname`	report what type of file it is.

Locating Commands

code	purpose
`type cmd`	show if `cmd` is a shell built-in or standalone program. ⁖ `type kill`. `type` is a built-in bash command, not a standalone shell util.
`which cmd`	show full path of a command, useful for checking if a program is installed, or if it's in the search path in `$PATH` environment variable.
`man cmd`	view documentation of a command. 【`q`】 to exit. 【`h`】 for help.
`apropos string`	search man pages.
`locate fname`	find a file by name (using the database see `man updatedb`). This is similar to `find dir paths -name "fname"` but much faster.
`updatedb`	update the database used by `locate`

unix find executables by searching the $PATH environment variable. Try echo $PATH. It is a list of dir paths. They are searched in order.

Excutable files must have executable bits on. That is, the “x”. For example, type ls -l /usr/bin to see them. 〔☛ Intro to Linux File Permission System〕

Install Programs/Debian-Package

The following are for Ubuntu and Debian derived Linux distro.

code	purpose
`apt-cache search name`	find package `name` for install by “apt-get”
`apt-cache show name`	describe package `name`
`apt-get install name`	install a new program. (usually used with `sudo` in front)
`apt-get remove name`	remove (un-install) a program.
`apt-get purge name`	remove a program and its config files.
`dpkg -l`	list all installed packages

code	purpose
`apt-get update`	sync package index files from sources. (need to do this regularly)
`apt-get upgrade`	upgrade all installed packages to latest versions (if any).
`apt-get dist-upgrade`	update OS kernel, and others.

〔☛ Linux: Package System {dpkg, apt-get} Tutorial〕

Typical install from source code:

gzip -d filename.tar.gz
tar xvf filename.tar

cd dirname
./configure
make
sudo make install # optional. This basically copy the binary to /usr/local/bin

Example: How to Build Emacs on Linux.

uname -a → print your OS info.
df --si → print disk usage.

〔☛ Linux: How to Find {kernel version, Distro, CPU, RAM, Disk Size} Info〕

Archive, Compression {tar, gzip}

code	purpose
`tar cvf new name.tar dirpath`	archive a folder.
`tar xvf filename.tar`	unarchive.
`gzip filename`	Compress a file.
`gzip -d filename`	Decompress a file.

code	purpose
`bzip2 filename`	Compress a file.
`bzip2 -d filename`	Decompress a file.
`xz filename`	Compress a file.
`xz -d filename`	Decompress a file.

〔☛ Linux: Compression How-to: tar gzip bzip2 xz 7zip rar zip〕

Text Processing

Version Control

Scripting

Fetching ＆ Sync Remote Files: rsync, unison, wget, curl

Managing Process

code	purpose
`ps -ef`	view running processes
`ps -ef \| grep name`	find a particular process
`kill pid`	quit a program that has process id `pid`
`kill -s 9 pid`	force quit a process
`top`	monitor processes with continuous update. `q` to quit.
`pstree`	show the process parent-child relationship

〔☛ Linux: Monitor Processes, “top” Tutorial〕
〔☛ Linux: Monitor Processes, “htop” Tutorial〕

Job Control

Linux: Job Control Tutorial

Sys Admin

code	purpose
`sudo command string`	run a command as “root” (“root” is the name of default admin account.)
`su`	switch to “root”
`sudo su root`	switch to “root”. (useful when root isn't setup as a login account. ⁖ default Ubuntu)

code	purpose
`chmod 664 filename`	change the perm bits. (664 = `rw-rw-r--`; typical text file perm bits)
`chown user name filename`	change owner of a file.
`chgrp group name filename`	change the group of a file.
`ln -s new path existing path`	make a symbolic link of a file. (symbolic link is file who's content is a path of another file.)
`ln new path existing path`	create hard link of a file. (Hard link makes 2 files pointing to the same index in the file system (hard disk).)
`shutdown -r 0`	restart machine now. (power off is `-P`)

〔☛ Linux: File Permission System Tutorial〕

code	purpose
`useradd user name`	create a new user account. (On Debian based Linuxes, there's higher-level “adduser” written in perl.)
`passwd user name`	change password for user.
`id user name`	show the id number of a user, and all groups he belongs to.
`cat /ect/passwd`	list all users
`getent group`	list all groups. See `getent --help`

〔☛ Linux Sys Admin: Managing Users ＆ Groups〕

code	purpose
`date`	show current date and time
`date --rfc-3339=seconds`	show time stamp in this format: “yyyy-mm-dd hh:mm:ss-07:00” the last are time offset to UTC.
`w`	show who is logged in.
`who -a`	list all users that have logged in recently.
`uptime`	show how long the system's been running.
`wc`	count the number of chars, words, lines. useful with `cat`, `grep`

code	purpose
`source fname`	execute a file `fname`. `source fname` is equivalent to `. fname`
`bash`	start a new bash. 【`Ctrl`+`d`】 to exit when done.
`echo $PATH`	View value of a environment variable `PATH`.
`env`	show all environment variables
`alias str="cmd";`	make `str` as shortcut for `cmd`. ⁖ `alias l="ls -al --color"`

〔☛ Linux: Show Open Files, 「lsof」 Tutorial〕

Image Processing

Generic Useful Bash Syntax

code	purpose
`cmd *.txt`	A asterisk “” means any character. `.txt` means all files ending in “.txt”. Can be used for any command that takes list of files or dir. See `man 7 glob`.
`cmd1 \| cmd2`	pass the output of `cmd1` to the input of `cmd2`
`cat filename \| cmd`	feed the content of `filename` to the input of `cmd`
`cmd > filename`	write the output to file
`cmd >> filename`	append output to file
`cat filename1 filename2 > new filename`	join contents of `filename1` `filename2` to `new filename`
`cmd1; cmd2; …`	run several commands.
`cmd1 && cmd2`	run `cmd1`, if success, then run `cmd2` (otherwise stop.) (the `&&` is a logical “and” operator. Unix commands returns 0 if success, else a integer error code.)
… `cmd` …	generate the output of `cmd` and use it in your whole command. ⁖ ls -l `which more`
`… &`	run a command in background.

Bash Keys

Linux: Bash Keys, Terminal Keys, Man Page Keys ⌨

Linux {Desktop, Window Manager} Overview

Intro to Linux Window Manager, Desktop Environment (Gnome, KDE, Xfce, xmonad, …)