Linux: Basic Shell Commands

By Xah Lee. Date: 2012-09-13. Last updated: 2017-04-18.

This is a list of most frequently used linux commands.

These are essential commands. Most of them are used everyday by every linux user.

The code here are based on Ubuntu Linux, but 99% of them work in any unix, including Mac OS X.

Navigate Directory

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
`cd ..`	go up one dir
`pwd`	show the current dir

Many of these command's argument can be either a file name (relative to current directory), or a full file path. For example, ls /usr/local/bin

You can set bash to show current dir path and time in your prompt.

[see Linux: Bash Prompt Setup]

File/Directory Manipulation

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. [see Linux: Show Directory Size: du]

Viewing Files

code	purpose
`cat fname`	display file content
`cat fname \| more`	view a file by page. Type 【`q`】 to exit. Type 【`h`】 for other keys.
`vi fname`	view a file. Type 【`Escape` `:` `q`】 to exit. [see vim Basics]
`head fname`	view the first few lines of a file. (most useful for big files, e.g. log file.)
`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. (For example, text, jpg, png, pdf, ….)

Locating Commands

code	purpose
`type cmd`	show if `cmd` is a shell built-in or standalone program. For example, `type kill`. The command `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 done automatically. Useful only if you just installed bunch of new commands.)

Linux find executable files 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. [see Linux: File Permission System]

Install Program/Package

The following are for Ubuntu Linux.

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.

[see Linux: How to Install/Remove Packages]

To install and compile a new command, here's the typical steps:

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.

[see Linux: Get System 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.

[see Linux: Compression How-to: tar gzip bzip2 xz 7zip rar zip]

Text Processing

Version Control

Fetching and 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. [see Linux: Monitor Processes: top]
`pstree`	show the process parent-child relationship

A better program for monitoring processes than “top” is “htop”. [see Linux: Monitor Processes, “htop”]

Job Control

Linux: Job Control

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. For example, 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`)

[see Linux: File Permissions]

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`

[see Linux: Users and 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`. For example, `alias l="ls -al --color"`

[see Linux: Show Opened Files, lsof]

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 take 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. For example, ls -l `which more`
`cmd &`	run the command `cmd` in background.
`echo $?`	show exit status of previous command.

Bash Keys

Linux: Bash Keys, Terminal Keys, Man Page Keys

Linux {Desktop, Window Manager} Overview

Linux: How to Switch to LXDE, Xfce

Shell Basics

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