Linux Tutorial by Example: Most Frequently Used Shell Commands

, 2012-09-13, …, 2014-10-30

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. Let me repeat in a different way: any professional unix sys admin or dev ops, would know every command on this page, by reflex.

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 directory. (careful!)
`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〕

Many of these command's argument can be either a file name (relative to current directory), or a full file path.

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 directory structure, useful for big projects. 〔➤ 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 (vim tutorial)〕
`head fname`	view the first few lines of a (big) file. (most useful for log files.)
`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. Try `type type`
`which cmd`	show full path of a command, useful for checking if a program is installed (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`. (this is doen automatically. Useful only if you just installed bunch of new commands.)

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 derived Linux distro. (Ubuntu is derived from Debian.)

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`	tar up a dir.
`tar xvf filename.tar`	untar.
`zip -r new name.zip dirname`	zip a dir
`unzip filename`	unzip

code	purpose
`gzip filename`	Compress a file.
`gzip -d filename`	Decompress a file.
`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. 〔➤ Linux: Monitor Processes, “top” Tutorial〕
`pstree`	show the process parent-child relationship

A better program for monitoring processes than “top” is “htop”. 〔➤ 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 (aka soft link) of a file. (symbolic link is basically a file path.)
`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 (Gnome, KDE, Xfce, …)