Getting Started with Bash#

Since Bash is the default shell on every system, the first thing you need to do to start using the bash shell is:

• Log into the system if it’s a server
• Open a terminal if it’s a laptop/computer

When you first open the terminal, you will see a prompt (usually $ or #).

How do you know if your shell is bash? Try typing the command echo $SHELL in your terminal. If you get /bin/bash, then you are using bash, or try typing help and press enter.

See? We just asked bash to execute the help command. This command will display the version of bash you are using, as well as a list of available commands in bash.

More often than not, you will never use the list of available commands in bash help, unless you are writing bash scripts. But, it will be useful if you want to know what you can do in bash.

99% of the time, you will use bash to navigate files and directories and run commands like ls, cd, and other common utility commands.

Navigating the File System#

To navigate the file system, you will use the ls command, which is available under /bin/ls. Since bash has the /bin folder in $PATH, you can run the ls command without typing /bin/ls.

ls is the command to list the contents of a directory. If you do not specify a directory, it will list the contents of the current directory.

You usually start in the /home or /Users folder on macOS. My home folder is currently /home/memet.

memet@zxce3 ~ $ ls
Desktop  Documents  Downloads  Music  Pictures  Public  Templates  Videos

To navigate to another directory, you can use the cd (change directory) command. If you want to go back to the previous directory, you can use the cd - command.

memet@zxce3 ~ $ cd Desktop
memet@zxce3 ~/Desktop $ cd -
memet@zxce3 ~ $ 

cd .. will take you to the parent directory, and cd ../.. will take you two levels up.

memet@zxce3 ~ $ cd ..
memet@zxce3 /home $ cd ../..
memet@zxce3 / $ 

Depending on your Bash configuration, you will see the current folder in the prompt (symbol $). If you are using a simpler prompt, you can use the pwd command to see the current directory.

memet@zxce3 ~ $ pwd
/home/memet

pwd stands for print working directory

Command Editing#

When you type a command in the terminal, you can use several keyboard shortcuts to edit the command you typed. You can use the arrow keys to move the cursor, and the backspace key to delete characters before the cursor. If you want to delete the entire command, you can use the Ctrl + u command. Pressing enter will execute the command you typed.

This is normal and acceptable, but something that wowed early UNIX/Linux users.

Keyboard shortcuts help you edit the command you typed, and this is very useful when you want to edit a long command without using the arrow keys.

• Ctrl + a will move the cursor to the beginning of the command
• Ctrl + e will move the cursor to the end of the command
• Ctrl + f will move the cursor one character to the right
• Ctrl + b will move the cursor one character to the left
• Ctrl + k will delete all characters after the cursor
• Ctrl + u will delete all characters before the cursor
• Ctrl + d will delete the character in front of the cursor

There are many more keyboard shortcuts you can use to edit the command you typed.

Autocomplete#

One of the most useful features in bash is autocompletion. It helps you type commands quickly and avoid typos. Try typing cd Doc and pressing tab. Bash will complete the command for you. If there are multiple options for the characters you typed, you can type more characters and press tab again.

memet@zxce3 ~ $ cd Do
Documents/  Downloads/
memet@zxce3 ~ $ cd Doc
memet@zxce3 ~ $ cd Documents/
memet@zxce3 ~/Documents $ 

Autocompletion also works for file and directory names. Try typing ls Doc and pressing tab. Bash will complete the directory name for you.

memet@zxce3 ~ $ ls Doc
Documents/  Downloads/
memet@zxce3 ~ $ ls Documents/
image.png  image2.png  image3.png

Autocompletion also works for commands

Shell Commands#

Using the shell, we can run commands available on our system. We can prefix commands with the full path (e.g., /bin/ls or /usr/bin/ls to list files and directories), but the shell has the concept of path, so we just need to type ls, and it will look for the command in the specified paths.

Commands accept arguments. For example, ls /bin will list all files in the /bin folder.

Parameters start with a dash (-) and can be combined. For example, ls -a will list all files, including hidden files (those starting with a dot .). ls -l will list files in a detailed format.

Commonly Used Commands#

There are many built-in commands on all systems, and they vary depending on whether it’s Linux/Unix or macOS or even the Linux distribution you are using.

However, let’s cover the most common and widely used ones.

When you encounter problems, such as not knowing a command or how to use it, you can use the man command to view the documentation for that command.

Here is a list of commonly used system commands:

Every file in Unix has permissions, and you can use the chmod command to change them (not covered here). The chown command changes the file owner.

cat, tail, and grep are very useful commands for files. cat displays the contents of a file, tail shows the end of a file, and grep searches for a string in a file.

find and locate are commands to search for files. find searches for files in the current directory, and locate searches for files across the entire system.

tar and gzip are commands to compress files. tar compresses files, and gzip compresses already compressed files.

pico, nano, vim, and emacs are commonly installed and used editors.

whereis and which are commands to find the location of commands. whereis finds the location of commands, and which finds the location of commands that will be executed.

There are many more commands you can use on your system, and these are some of the commands you will likely use frequently.

Running Commands#

The cd and ls commands, as explained above, are found in the /bin folder. You can execute any file as long as it is an executable file by typing the full path, for example, /bin/pwd. Commands do not require the /bin folder, and you can execute files in the current folder with the ./ path indicator.

For example, if you have a file yamete in the /home/memet/scripts folder, you can run:

cd /home/memet/scripts

Then run ./yamete to execute the file.

Or you can run /home/memet/scripts/yamete from Bash, regardless of the current folder.

Jobs#

When you run any command, if it is a long-running program, your shell is taken over by that program. You can stop the command by pressing ctrl + c.

You can run commands in the background by adding & at the end of the command. For example, sleep 1000 & will run the sleep command for 1000 seconds in the background.

You can see a list of running commands with the jobs command. You can stop commands with the kill and killall commands.

memet@zxce3:~$ sleep 1000 &
[1] 1234
memet@zxce3:~$ jobs
[1]+  Running                 sleep 1000 &
memet@zxce3:~$ kill 1234
memet@zxce3:~$ jobs
[1]+  Terminated              sleep 1000 &

Background commands will stop if you close your shell.

Another useful command is ps to see a list of running processes.

memet@zxce3:~$ ps
  PID TTY          TIME CMD
  123 pts/0    00:00:00 bash
  456 pts/0    00:00:00 ps

And top to see a real-time list of running processes.

A job process can be stopped using kill <PID>.

Command History#

Pressing the up arrow key will show the commands you previously ran. This is a shell feature. Pressing the down arrow key will help you navigate back to the most recently run commands. Pressing enter will run the command again.

This is quick access to the commands you previously ran. Running the history command will display a list of all the commands you previously ran.

memet@zxce3:~$ history
    1  ls
    2  cd /home/memet
    3  ls
    4  cd /home/memet/scripts
    5  ls
    6  history

When you start typing a command, Bash can autocomplete the command you previously ran by referencing the commands you previously ran. Try pressing esc and then tab.

Honestly, I found the implementation of the fish shell to be better and easier. Maybe I’ll discuss it later.

Setting the Default Shell#

There are many shells besides Bash, such as Fish, Zsh, TCSH, and others. Each user on the system can choose the shell they want. You can change the default shell with the chsh command.

memet@zxce3:~$ chsh
Changing shell for memet.
Password:
New shell [/bin/bash]: /bin/zsh
memet@zxce3:~$ echo $SHELL
/bin/zsh

Customizing Bash#

As mentioned earlier, you may (or may not) see the current directory in the bash prompt. Where is this determined? In the Bash configuration file!

There is some confusion here because Bash uses different configuration files for different scenarios, and it also reads multiple configuration files.

Let’s discuss this confusion one by one. First, there is a big difference between whether Bash is initialized as a login shell or a non-login shell. A login shell means that the system is not running in a GUI (Graphical User Interface) and you log into the system through the shell. This is in the context of a server, for example.

In this case, Bash reads the /etc/profile configuration file.

And look in the user’s home folder, there are configuration files.

~/.bash_profile
~/.bash_login
~/.profile

Where ~ is the user’s home folder (this is automatically translated by Bash).

This means that if there are .bash_profile, ~/.bash_login, and ~/.profile files in the user’s home folder, Bash will read these files. If there are .bash_profile and ~/.bash_login files in the user’s home folder, Bash will read the .bash_profile file first.

If Bash is run as a non-login shell, Bash will read the ~/.bashrc configuration file.

Environment Variables#

Sometimes you have programs that use environment variables. These are values that can be set outside the program, and the program can access them. An API key, for example. Or a path you need to run the program.

You can set an environment variable with syntax like this.

VARIABLE_NAME=VALUE

The value can contain spaces and special characters by using quotes.

VARIABLE_NAME="THIS IS THE VALUE"

Bash scripts can use variables with the syntax $VARIABLE_NAME.

memet@zxce3:~$ VARIABLE_NAME="THIS IS THE VALUE"
memet@zxce3:~$ echo $VARIABLE_NAME
THIS IS THE VALUE

Bash also provides some variables you can use, such as:

• $HOME for the user’s home folder
• $PATH for the path accessible by programs
• $SHELL for the currently running shell
• $USER for the username

You can see the contents of these variables using the echo command.

memet@zxce3:~$ echo $HOME
/home/memet
memet@zxce3:~$ echo $SHELL
/bin/bash

Special Environment Variable: $PATH#

$PATH is a variable that contains a list of paths accessible by programs. The shell will look at this when you type a command. Folders are separated by colons : and are ordered from left to right - Bash will look at the first one, search for the command there, and if not found, look at the second one, and so on.

My current path is like this.

memet@zxce3:~$ echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin/:/bin:/usr/sbin:/usr/bin:/usr/games:/usr/local/games:

You can edit this in the ~/.bashrc file by adding the path you want.

PATH=$PATH:/home/memet/scripts

Aliases#

Aliases are shortcuts for commands you frequently use. For example, you can create an alias for git status with gst.

memet@zxce3:~$ alias gst='git status'
memet@zxce3:~$ gst
On branch master
Your branch is up to date with 'origin/master'.

To define an alias, use the syntax like this.

alias <alias>=<command>

If you want to create an alias for a long command, you can use quotes.

alias <alias>="<command>"

You can also define aliases in the ~/.bashrc file.

Be careful with quotes if you have variables in the command: using double quotes will resolve the variable at definition time, using single quotes will resolve the variable at call time. These are different.

alias lsnow="ls $PWD"
alias lslater='ls $PWD'

$PWD refers to the current folder, and if you type lsnow and lslater, you will get different results. lsnow will display the contents of the current folder, while lslater will display the contents of the folder where you defined the alias.

Advanced Command Line Features#

memet@zxce3:~$ ls a*
a.txt ab.txt  abc.txt

memet@zxce3:~$ ls *.txt
a.txt ab.txt  abc.txt

memet@zxce3:~$ ls *b* *c*
a.txt ab.txt  abc.txt

ls 1> output.txt 2> error.txt
ls > output.txt 2> error.txt

ls &> output.txt

ls 1> output.txt 2>&1

memet@zxce3:~$ top &
[1] 1234

memet@zxce3:~$ ps
  PID TTY          TIME CMD
 1234 pts/0    00:00:00 top
 1235 pts/0    00:00:00 bash
 1236 pts/0    00:00:00 ps
memet@zxce3:~$ fg 1234
top

memet@zxce3:~$ sleep 5; echo "done"
done

memet@zxce3:~$ echo "hello" > output.txt
memet@zxce3:~$ wc < output.txt
1 1 6 output.txt

memet@zxce3:~$ echo "hello" | wc
1 1 6

memet@zxce3:~$ false && echo "success"
memet@zxce3:~$ true && echo "success"
success

memet@zxce3:~$ false || echo "success"
success
memet@zxce3:~$ true || echo "success"
memet@zxce3:~$

memet@zxce3:~$ !true
false
memet@zxce3:~$ !false
true

memet@zxce3:~$ (true && false) || true
true
memet@zxce3:~$ ! (true && false) || true
false

#!/bin/bash
echo "hello"

#!/usr/bin/fish
echo "hello"