Terminal (Bash) - Customization (.bashrc)

Every time you create a new terminal the code at the file .bashrc is executed. This allows us to run commands add or change variables and do other types of things.

PATH

PATH is an environment variable. Used by Unix-like operating systems, DOS, OS/2, and even Microsoft Windows. It is used to specify a set of directories where executable programs are located.

To add a directory to the path you just need to redefine the variable with a new value:

PATH=$PATH:<directory_path>

or

PATH=<directory_path>:$PATH

Example, imagine you just downloaded NodeJS and moved it to the "/opt" directory. Then to add NodeJS executables to the PATH, and assuming that those executables are inside the "bin" directory, you just need to add the following line to your .bashrc

PATH=/opt/nodejs/bin:$PATH

Aliases

Aliases allow you to create or override commands so you don't need to type a long sequence of characters. This is very useful and allows you to save a lot of time.

For example, if you want to show the directory files (ls) including the files or directories that start with a '.'.

alias la='ls -a'

You can create all kinds of alias, you just need to make sure you don't use a name already in use. Another good example of use is when you have a project directory and you don't want to remember exactly the location. In that case, you just create an alias that uses the cd command:

alias project1='cd ~/projects/project1'

Usefull aliases

alias	Description
alias ls="ls -CF"	Display files in columns and with a file type indicator
alias lsl="ls -lhFA	less"
alias ..="cd .."
alias fhere="find . -name "	find files in current directory
alias update="sudo apt update && sudo apt upgrade -y"
alias df="df -Tha --total"	Show disk usage
alias free="free -mt"	Free comand with human-readable units
alias ps="ps auxf"	Process table

Prompt

The Bash prompt is stored in the PS1 variable. So to change how the prompt is presented you need to change this variable. Usually there is more than one assign to the variable, for example:

if [ "$color_prompt" = yes ]; then
        PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
else
    PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
fi

Make sure you change the one being executed, in the previous example if the prompt shows up with colours then is the first one (inside the if) you need to change.

Before changing the PS1 variable make sure you create a backup variable with the default value, example:

PS1BACKUP='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

Special characters

As you might have seen there is a lot of weird characters in the PS1. So let's start by understanding what each one does.

Character	Description
\a	A bell character
\d	The date, in "Weekday Month Date" format (e.g., "Tue May 26")
\D{format}	The format is passed to strftime(3) and the result is inserted into the prompt string; an empty format results in locale-specific time representation. The braces are required
\e	An escape character
\h	The hostname, up to the first '.'
\H	The hostname
\j	The number of jobs currently managed by the shell
\l	The basename of the shell’s terminal device name
\n	A newline
\s	The name of the shell, the basename of $0 (the portion following the final slash)
\t	The time, in 24-hour HH:MM:SS format
\A	The time, in 24-hour HH:MM format
\u	The username of the current user
\v	The version of Bash (e.g., 2.00)
\w	The current working directory, with $HOME abbreviated with a tilde (uses the $PROMPT_DIRTRIM variable)
\nnn	The character whose ASCII code is the octal value nnn
\	A backslash
[	Begin a sequence of non-printing characters. This could be used to embed a terminal control sequence into the prompt
]	End a sequence of non-printing characters
Complete List

Text appearence

You can also change the text format, colour and background. The way it works is simple but it makes the string very confusing for anyone that doesn't know what is happening. For example, the previous example:

${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ 

It's easier to read if we split it into blocks, like this:

${debian_chroot:+($debian_chroot)}
\[\033[01;32m\]\u@\h
\[\033[00m\]:
\[\033[01;34m\]\w
\[\033[00m\]\$ 

Let's take a look at the second line. What is happening is that we are defining the text "\u@\h" to be bold and green. The text format is specified between the \[ and \] characters. Inside, we must have either \033[ or \e[ to indicate that the values refer to colour information. Now we can have values for the text format, colour and background colour if none is given the default value is used. At the end of the tag, we must have an m to indicate the end of the colour information.

Structure example:

\[\033[TEXT_FORMAT;COLOR;BACK_COLORm\]

Example:

\[\033[01;33m\]

Tables with values

Text Format

Value	Text Format
0	Normal Text
1	Bold or Light Text
2	Dim Text
4	Underlined Text
5	Blinking Text
7	Reversed Text
8	Hidden Text

Color

Value	Color
30	Black
31	Red
32	Green
33	Yellow
34	Blue
35	Purple
36	Cyan
37	White

Background Color

Value	Background Color
40	Black background
41	Red background
42	Green background
43	Yellow background
44	Blue background
45	Purple background
46	Cyan background
47	White background