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Ubuntu Bash Basics

Introduction​

Bash (Bourne Again SHell) is the default command-line interpreter for Ubuntu and most Linux distributions. It serves as an interface between you and the operating system, allowing you to execute commands, run programs, and automate tasks. Mastering Bash basics is essential for anyone working with Ubuntu or any Linux-based system.

This guide will introduce you to the fundamental concepts and commands of the Bash shell, helping you become comfortable with the command line interface in Ubuntu.

Accessing the Terminal​

Before diving into Bash commands, you need to know how to access the terminal in Ubuntu:

  1. Press Ctrl+Alt+T (keyboard shortcut)
  2. Search for "Terminal" in the Applications menu
  3. Right-click on the desktop and select "Open Terminal" (if available)

When you open the terminal, you'll see a prompt that typically looks like:

username@hostname:~$

This indicates:

  • username: Your user account
  • hostname: Your computer's name
  • ~: Your current directory (~ represents your home directory)
  • $: Indicates you're logged in as a regular user (a # would indicate root user)

Basic Navigation Commands​

Viewing Current Directory​

To see your current location in the file system:

bash
pwd

Output:

/home/username

The pwd command (Print Working Directory) shows your current location in the file system.

Listing Files and Directories​

To view the contents of a directory:

bash
ls

Output:

Documents  Downloads  Music  Pictures  Videos

Common options for ls:

bash
ls -l    # Long format with details

Output:

total 20
drwxr-xr-x 2 username username 4096 Mar 10 15:30 Documents
drwxr-xr-x 2 username username 4096 Mar 10 15:30 Downloads
drwxr-xr-x 2 username username 4096 Mar 10 15:30 Music
drwxr-xr-x 2 username username 4096 Mar 10 15:30 Pictures
drwxr-xr-x 2 username username 4096 Mar 10 15:30 Videos
bash
ls -a    # Show all files (including hidden ones)

Output:

.  ..  .bash_history  .bash_logout  .bashrc  Documents  Downloads  Music  Pictures  Videos
bash
ls -lh   # Human-readable file sizes

Output:

total 20K
drwxr-xr-x 2 username username 4.0K Mar 10 15:30 Documents
drwxr-xr-x 2 username username 4.0K Mar 10 15:30 Downloads
drwxr-xr-x 2 username username 4.0K Mar 10 15:30 Music
drwxr-xr-x 2 username username 4.0K Mar 10 15:30 Pictures
drwxr-xr-x 2 username username 4.0K Mar 10 15:30 Videos

Changing Directories​

To navigate between directories:

bash
cd Documents

No output is shown when the command succeeds.

Useful cd shortcuts:

bash
cd          # Go to home directory
cd ~        # Go to home directory (same as above)
cd ..       # Go up one level
cd ../..    # Go up two levels
cd -        # Go to previous directory

File Operations​

Creating Files and Directories​

To create a new directory:

bash
mkdir my_project

To create a new empty file:

bash
touch myfile.txt

To create multiple directories at once:

bash
mkdir -p projects/web/html

The -p flag creates parent directories if they don't exist.

Copying Files​

Basic syntax:

bash
cp source destination

Example:

bash
cp myfile.txt Documents/

To copy directories recursively:

bash
cp -r my_project backup_project

Moving and Renaming Files​

The mv command is used for both moving and renaming:

bash
mv myfile.txt Documents/    # Move file to Documents directory
mv myfile.txt newname.txt   # Rename file

Removing Files and Directories​

To delete a file:

bash
rm myfile.txt

To delete an empty directory:

bash
rmdir my_project

To delete a directory and all its contents:

bash
rm -r my_project

Warning: Be extremely careful with rm -r and especially rm -rf (which forces deletion without prompting). There's no "recycle bin" or "undo" in the terminal.

Viewing File Content​

Displaying Entire Files​

To display the contents of a file:

bash
cat myfile.txt

Output:

This is the content of my file.
It has multiple lines.

Viewing Large Files​

For large files, use pagers like less to view content one screen at a time:

bash
less myfile.txt

Navigate in less:

  • Press Space or Page Down to go forward
  • Press b or Page Up to go backward
  • Press q to quit

Viewing File Beginnings and Endings​

To see the first few lines of a file:

bash
head myfile.txt

To see the last few lines:

bash
tail myfile.txt

To specify the number of lines:

bash
head -n 5 myfile.txt    # First 5 lines
tail -n 10 myfile.txt   # Last 10 lines

Bash Special Characters​

Bash uses several special characters that have specific meanings:

CharacterDescription
*Wildcard - matches any characters
?Wildcard - matches any single character
>Redirect output to a file (overwrite)
>>Redirect output to a file (append)
``
&Run a command in the background
;Command separator
$Variable expression
\Escape character

Examples of Special Characters​

Using wildcards:

bash
ls *.txt         # List all .txt files
ls document?.txt # Lists document1.txt, documentA.txt, etc.

Redirecting output:

bash
echo "Hello World" > greeting.txt   # Write to file
echo "More text" >> greeting.txt    # Append to file

Using pipes:

bash
ls -l | grep "txt"   # List only files containing "txt"

Environment and Variables​

Checking Environment Variables​

To see all environment variables:

bash
env

To see a specific variable:

bash
echo $HOME

Output:

/home/username

Setting Variables​

Set a temporary variable:

bash
MYVAR="Hello World"
echo $MYVAR

Output:

Hello World

Command History​

Viewing Command History​

To see previously executed commands:

bash
history

Output:

1  pwd
2  ls
3  cd Documents
4  touch file.txt
5  history

Searching Command History​

Press Ctrl+R and type to search through your command history.

Re-executing Commands​

bash
!5        # Execute command number 5 from history
!!        # Execute the last command again
!cd       # Execute the most recent command starting with "cd"

Basic Text Processing​

Searching in Files​

To search for text in files:

bash
grep "search_term" filename.txt

Output:

This line contains the search_term in it.

Common grep options:

bash
grep -i "term" file.txt    # Case-insensitive search
grep -r "term" directory/  # Recursive search through directories
grep -n "term" file.txt    # Show line numbers

Simple Text Editing​

While there are advanced text editors like vim and nano, you can do simple edits with stream editors:

bash
sed 's/old/new/' file.txt  # Replace first occurrence of "old" with "new"
sed 's/old/new/g' file.txt # Replace all occurrences

Process Management​

Viewing Running Processes​

To see currently running processes:

bash
ps

Output:

  PID TTY          TIME CMD
 1234 pts/0    00:00:00 bash
 5678 pts/0    00:00:00 ps

For a more detailed view:

bash
ps aux

For a dynamic, real-time view:

bash
top

Killing Processes​

To terminate a process:

bash
kill 1234    # Kill process with PID 1234

For stubborn processes:

bash
kill -9 1234

Command Chaining​

Bash allows you to chain commands in various ways:

bash
command1 && command2    # Run command2 only if command1 succeeds
command1 || command2    # Run command2 only if command1 fails
command1 ; command2     # Run command1 then command2 regardless

Example:

bash
mkdir project && cd project && touch readme.txt

This creates a directory, changes into it, and creates a file, but only if each previous step succeeds.

Permissions​

Viewing Permissions​

File permissions are shown in the output of ls -l:

bash
ls -l myfile.txt

Output:

-rw-r--r-- 1 username groupname 123 Mar 10 15:30 myfile.txt

The first ten characters represent:

  • File type (1st character): - for regular file, d for directory
  • Owner permissions (2nd-4th): rw- means read and write, no execute
  • Group permissions (5th-7th): r-- means read-only
  • Others permissions (8th-10th): r-- means read-only

Changing Permissions​

To change permissions:

bash
chmod permissions filename

Using symbolic mode:

bash
chmod u+x script.sh    # Add execute permission for the user
chmod go-w file.txt    # Remove write permission for group and others
chmod a+r file.txt     # Add read permission for all

Using octal mode:

bash
chmod 755 script.sh    # rwxr-xr-x
chmod 644 file.txt     # rw-r--r--

Bash Scripting Basics​

While full bash scripting deserves its own tutorial, here's a simple example:

Create a new file called hello.sh:

bash
touch hello.sh

Edit it with a text editor or use this command:

bash
echo '#!/bin/bash
echo "Hello, $USER!"
echo "Today is $(date)"
echo "Current directory: $(pwd)"' > hello.sh

Make it executable:

bash
chmod +x hello.sh

Run it:

bash
./hello.sh

Output:

Hello, username!
Today is Thu Mar 13 10:30:45 UTC 2025
Current directory: /home/username

Working with Archives​

Creating Archives​

To create a tar archive:

bash
tar -cvf archive.tar file1 file2 directory/

To create a compressed tar archive:

bash
tar -czvf archive.tar.gz file1 file2 directory/

Extracting Archives​

To extract a tar archive:

bash
tar -xvf archive.tar

To extract a compressed tar archive:

bash
tar -xzvf archive.tar.gz

Using Man Pages​

The man command displays the manual for a command:

bash
man ls

This opens documentation explaining all options for the ls command.

Navigation in man pages works the same as in less:

  • Press Space to page down
  • Press b to page up
  • Press / followed by a term to search
  • Press q to quit

Command Structure Visualization​

Summary​

This guide has covered the essential Bash commands and concepts that every Ubuntu user should know:

  • Navigating the file system with pwd, ls, and cd
  • Managing files and directories with mkdir, touch, cp, mv, and rm
  • Viewing file content with cat, less, head, and tail
  • Understanding special characters and redirection
  • Working with environment variables
  • Managing command history
  • Basic text processing with grep and sed
  • Process management with ps, top, and kill
  • Chaining commands
  • Understanding and modifying file permissions
  • Basic Bash scripting
  • Working with archives
  • Using man pages for help

Mastering these basics will make you comfortable using the Ubuntu terminal and provide a solid foundation for more advanced shell scripting topics.

Additional Resources and Exercises​

Practice Exercises​

  1. Create a directory structure for a web project with folders for HTML, CSS, and JavaScript files.
  2. Write a simple bash script that creates a backup of a specified directory.
  3. Use grep to find all occurrences of a specific word in all text files in a directory.
  4. Create a compressed archive of your home directory (excluding large subdirectories).
  5. Set up environment variables that you might use in development work.

Further Learning Resources​


If you spot any mistakes on this website, please let me know at [email protected]. I’d greatly appreciate your feedback! :)