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The Bash shell (Bourne Again SHell) is a widely used command-line interpreter for Unix-like operating systems. It provides a powerful interface for users to interact with the system, execute commands, and run scripts.

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Identifying the Bash Shell

/bin/bash is very popular because it offers a rich set of features, including command history, tab completion, and scripting capabilities.
To check which shell you’re currently using, run the following command: 
karchunt@kcserver:~$ echo $SHELL
/bin/bash
You can also use the env command to confirm the current shell: 
karchunt@kcserver:~$ env | grep SHELL
SHELL=/bin/bash

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Changing the Default Shell

If you want to change your default shell to Bash, use the chsh (change shell) command. 
karchunt@kcserver:~$ chsh
Password:
Changing the login shell for karchunt
Enter the new value, or press ENTER for the default
        Login Shell [/bin/bash]: /bin/sh
After running chsh, you need to log out and log back in for the shell change to take effect.

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Bash Features

Bash supports command auto-completion, which lets you quickly complete commands and file names by pressing the Tab key.
karchunt@kcserver:~$ ls folder
folder1/ folder3/
Pressing Tab after typing folder will auto-complete to the available matching directory names. If there is no ambiguity, it completes automatically.
Bash maintains a history of commands you’ve executed. Access it with the history command or by pressing the Up and Down arrow keys to cycle through previous commands.
karchunt@kcserver:~$ history
  1  ls
  2  cd folder1
  3  nano file.txt
  4  history
Bash allows you to create shortcuts for frequently used commands using the alias command.
karchunt@kcserver:~$ alias ll='ls -la'
karchunt@kcserver:~$ ll
To see all currently defined aliases, run alias with no arguments:
karchunt@DESKTOP-CCAQ09F:~$ alias
alias alert='notify-send --urgency=low -i "$([ $? = 0 ] && echo terminal || echo error)" "$(history|tail -n1|sed -e '\''s/^\s*[0-9]\+\s*//;s/[;&|]\s*alert$//'\'')"\''
alias egrep='egrep --color=auto'
alias fgrep='fgrep --color=auto'
alias grep='grep --color=auto'
alias l='ls -CF'
alias la='ls -A'
alias ll='ls -la'
alias ls='ls --color=auto'
To make an alias permanent, add its definition to your ~/.bashrc file.

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Customizing the Bash Prompt

When you log in to a Bash shell, you typically see ~$ as your prompt. You can customize this by modifying the PS1 variable in your ~/.bashrc file. Check the current value of PS1: 
karchunt@kcserver:~$ echo $PS1
\[\e]0;\u@\h: \w\a\]${debian_chroot:+(${debian_chroot})}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$
Common escape sequences for prompt customization:
SequenceDescription
\uUsername
\hHostname
\wCurrent working directory
\dDate
\tCurrent time
Example — set a custom prompt directly in the terminal: 
karchunt@kcserver:~$ PS1="\d \u@\h:\w\$"
Thu Jan 29 karchunt@kcserver:~$
To make prompt changes permanent, add the PS1 assignment to your ~/.bashrc file so it applies on every new shell session.

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