Introduction to basic Unix commands

Overview

Time estimation: 2H

Version: main

Last update: 2025-11-28

Questions

• What is a command shell and why would I use one?

• How can I move around on my computer?

• How can I see what files and directories I have?

• How can I specify the location of a file or directory on my computer?

Objectives

• Describe key reasons for learning shell.

• Navigate your file system using the command line.

• Access and read help files for bash programs and use help files to identify useful command options.

• Demonstrate the use of tab completion, and explain its advantages.

This tutorial will help you develop proficiency in the necessary Unix shell concepts.

What is a command shell?

On Unix, every user has a unique user name. When they log onto the system, they are placed in a home directory, which is a portion of the disk space reserved just for them. When you log onto a Unix system, your main interface to the system is called the Unix Shell. This is the program that presents you with the dollar sign ($) prompt. This prompt means that the shell is ready to accept your typed commands. It is often preceded by the user name as well as the current directory.

Unix commands are strings of characters typed in at the keyboard. To run a command, you just type it in and press the Enter key. We will look at several of the most common commands below. Commands often have parameters, e. g. a file to work on. These are typed in after the command and are separated by spaces, e. g. less pi_results.txt opens the file pi_results.txt for reading.

In addition, Unix extends the power of commands by using special flags or switches. Switches are usually preceded with a dash (-), e. g. ls -lh.

List of commands

Command	Description
pwd	print current (working) directory
ls	list contents of the current directory
⤷ -l	long (detailed) listing
⤷ -h	with human readable numbers
cd	change to another directory
mkdir	make a new directory
mv	move or rename a file or directory
cp	copy file
⤷ -r	copy directory tree (recursively)
file	determine file type
echo	print a line of text
head	View the first 10 lines of a file
sort	Sort lines of text files
less	display contents of a file (press q to quit)
tail	output the last part of a file
⤷ -f	follow appended data as the file grows
grep	list text lines containing a particular string of text
⤷ -v	output only non-matching lines
wc	count lines, words, and bytes in a file
cat	concatenate (combine) two or more files
df	show disk free information
⤷ -h	with human readable numbers
find	find files in a directory tree
man	display program manual for a command
ps -x	list one’s own running programs / processes (extended list)
kill	kill process
⤷ -9	kill process immediately (SIGKILL=9)
rm	remove a file
⤷ -r	remove a directory tree (recursively)
rmdir	remove an empty directory
chmod	change mode (security permissions) of file or directory
⤷ ugo+-rwx	user (owner), group, other (world), add(+), remove(-), read, write, execute
./myprogram	run the local executable file myprogram
sed 's/ab/cd/'	transform text, e. g. replace all occurrences of ‘ab’ with ‘cd’
nano	Command line text file editor
⤷ Ctrl-x	By using the key combination Ctrl-x in the editor, you can exit the editor and optionally save the file.
wget	network downloader (downloads files from the Web)
gzip	compress a file
gunzip	uncompress a file
*	wildcard representing any combination of characters
Places
~	your home directory
.	current directory
..	parent directory
Pipes
>	send output to a file
>>	append (add) output to a file
\|	pipe output from one command as input to another

Download as PDF or separate MarkDown.

Tutorial

During this tutorial you will use many of the commands above. Your task is to identify the correct commands and execute them. Feel free to experiment. Take a look at the solution if absolutely necessary.

This tutorial is based on the tutorial that was created by the de.NBI Cloud Bielefeld administrators. The first two sections (01 and 02) describe how to access the workshop environment for this tutorial. Participants need a web browser and an active ELIXIR account.

{ % include _tutorials/unix-course/main/part1.md %}

{ % include _tutorials/unix-course/main/part2.md %}

{ % include _tutorials/unix-course/main/part3.md %}

Key Points

• The shell gives you the ability to work more efficiently by using keyboard commands rather than a GUI.

• Useful commands for navigating your file system include: ls, pwd, and cd.

• Most commands take options (flags) which begin with a -.

• Tab completion can reduce errors from mistyping and make work more efficient in the shell.

Contributions

Author(s): Christian Henke, Peter Belmann, Jan Krueger, Nils Hoffmann, Sebastian Juenemann, Viktor Rudko