Setup

Shell environment

When you log in, bash configures your environment before displaying the prompt. It reads a series of configuration files called environment files or startup files. Bash starts in one of three ways:

• Default login: a text-only login with no GUI
• Interactive shell: a subshell spawned from a GUI terminal
• Non-interactive shell: a shell started to run a script

Environment variables

Environment variables store information about the current shell session, such as the current user, home directory, and default editor. View them with any of the following commands:

Environment files

User environment files are copied from /etc/skel at account creation. Users can edit them afterward. Bash reads these files in order and stops at the first one it finds:

1. .bash_profile
2. .bash_login
3. .profile

.bashrc is not read directly by bash at login. Instead, one of the files above sources it explicitly. For example, a typical .bash_profile contains:

if [ -f ~/.bashrc ]; then
    . ~/.bashrc
fi

This means .bashrc runs at every interactive login. It also runs automatically when a non-interactive shell starts, making it the right place for aliases, functions, and environment settings you want available in every session.

Global files

Global environment files apply to all users on the system:

• /etc/profile
• /etc/profile.d/ (individual .sh files, run during login)
• /etc/bash or /etc/bash.bashrc (varies by distribution)

sudo vim /etc/profile.d/custom-path.sh

export PATH="$PATH:/opt/myapp/bin"

Set default text editor

Ubuntu sets nano as the default editor. Run update-alternatives to select a different one. The command presents a numbered list of installed editors. Enter the number for your preferred editor and press Enter:

sudo update-alternatives --config editor
There are 4 choices for the alternative editor (providing /usr/bin/editor).

  Selection    Path                Priority   Status
------------------------------------------------------------
  0            /bin/nano            40        auto mode
  1            /bin/ed             -100       manual mode
  2            /bin/nano            40        manual mode
* 3            /usr/bin/vim.basic   30        manual mode
  4            /usr/bin/vim.tiny    15        manual mode

Press <enter> to keep the current choice[*], or type selection number:

Enable bash completion globally

Bash completion is often disabled by default in /etc/bash.bashrc. To enable it for all users, uncomment the following block in that file:

sudo vim /etc/bash.bashrc

# enable bash completion in interactive shells
if ! shopt -oq posix; then
  if [ -f /usr/share/bash-completion/bash_completion ]; then
    . /usr/share/bash-completion/bash_completion
  elif [ -f /etc/bash_completion ]; then
    . /etc/bash_completion
  fi
fi

Change hostname

hostnamectl sets the system hostname. The change takes effect immediately and persists across reboots:

hostnamectl set-hostname mylittlecloudbox

Set timezone

The system timezone affects scheduled tasks and timestamps in /var/log. Use timedatectl to view and change it.

View the current timezone:

timedatectl
               Local time: Sun 2024-12-01 17:15:21 UTC
           Universal time: Sun 2024-12-01 17:15:21 UTC
                 RTC time: Sun 2024-12-01 17:15:21
                Time zone: Etc/UTC (UTC, +0000)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

List available timezones:

timedatectl list-timezones

Set a new timezone and verify:

sudo timedatectl set-timezone America/New_York

timedatectl
               Local time: Sun 2024-12-01 12:15:57 EST
           Universal time: Sun 2024-12-01 17:15:57 UTC
                 RTC time: Sun 2024-12-01 17:15:57
                Time zone: America/New_York (EST, -0500)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

Dot files

Dot files are hidden configuration files stored in your home directory. Their names begin with ., which causes them to be hidden from standard directory listings. Run ls -a to view them. Common dot files:

.bashrc

.bashrc runs every time you open an interactive bash terminal. A common pattern is to source .profile from .bashrc, then load other dot files from .profile to keep each file focused on one concern.

Source .profile only when an interactive terminal is present:

[ -n "$PS1" ] && source ~/.profile

.profile

.profile runs at login and is a good place to load OS-specific settings or source other dot files. The following pattern sources each dot file only if it exists and is readable:

for file in ~/.{exports,aliases,functions,extra}; do
    [ -r "$file" ] && source "$file"
done
unset file

.aliases

.aliases keeps all shell aliases in one place, separate from .bashrc. It is sourced by .profile at login. For example, a set of git shorthand aliases:

alias gs="git status"
alias gb="git branch"
alias gc="git commit -am"
alias gp="git push"

.exports

.exports stores environment variable definitions, keeping them separate from other configuration. It is sourced by .profile at login. For example, set the Go workspace path:

export GOPATH="$HOME/go-workspace"

.vimrc

.vimrc stores your personal vim configuration. Settings here apply every time you open vim. For a full reference, open vim and run :help vimrc-intro. See the vim page for common settings.

.gitignore

.gitignore lists file patterns that git should not track. Place it in the root of a repository. For example, ignore compiled binaries and environment files:

*.out
.env

Chain dot files together

At login, bash reads .bashrc, which sources .profile. .profile then sources each specialized dot file if it exists. This keeps each file focused on one concern.

.bashrc sources .profile:

# ~/.bashrc
[ -n "$PS1" ] && source ~/.profile

.profile sources the specialized dot files:

# ~/.profile
for file in ~/.{exports,aliases,functions,extra}; do
    [ -r "$file" ] && source "$file"
done
unset file

.exports defines environment variables:

# ~/.exports
export GOPATH="$HOME/go-workspace"
export PATH="$PATH:$GOPATH/bin"

.aliases defines shorthand commands:

# ~/.aliases
alias gs="git status"
alias gb="git branch"
alias gc="git commit -am"
alias gp="git push"

Prompt Statement (PS)

The Prompt Statement variables control how bash displays prompts. Add customizations to .bashrc to make them permanent across sessions.

PS1

PS1 is the default interactive prompt displayed before every command. It supports escape sequences for dynamic content such as the username, hostname, and current directory. For a complete list of options, see the phoenixNap bash prompt guide.

PS2

PS2 is the continuation prompt displayed when a command spans multiple lines. The default value is >. Set a custom value to make multi-line input easier to read:

export PS2="continue-> "
ls /etc/ \
continue-> line 2 \
continue-> line 3 \
continue-> end;

PS3

PS3 customizes the prompt shown by the select command, replacing the default #?. For a practical example, see the Geek Stuff bash prompt guide.

PS4

PS4 customizes the prefix printed by debug mode. Debug mode runs a script with set -x, which causes bash to print each command before executing it. This is useful for tracing what a script does line by line. The default prefix is +. Set PS4 to include the line number to make the output easier to follow.

Default output:

+ echo 'PS4 demo script'
PS4 demo script
+ ls -l /etc
+ wc -l
229

Set a custom PS4 and compare the output:

export PS4='Line: $LINENO++ '

Line: 7++ echo 'PS4 demo script'
PS4 demo script
Line: 8++ ls -l /etc
Line: 8++ wc -l
229

PROMPT_COMMAND

PROMPT_COMMAND holds a command that bash runs before displaying PS1. Use it to show dynamic information such as the current time before every prompt.

Print the time before each prompt on its own line:

export PROMPT_COMMAND="date +%k:%M:%S"
11:12:35
user@machine:~$ ls
...
11:12:43

Print the time on the same line as PS1:

export PROMPT_COMMAND="echo -n [$(date +%k:%M:%S)]"
[11:12:35]user@machine:~$