Environment

Environment setup

After user authenticates to the system and before the bash shell prompt displays, the user environment is configured.
When you start a bash shell, bash checks several files for configuration, called environment files (also called startup files)
Can start a shell in 3 ways:
- Default login (login to server w no GUI)
- Interactive shell spawned as subshell (such as from a GUI)
- non-interactive shell, such as when running a script

Environment variables

Store info about the current shell session

# user less pager
set
env
printenv
# view what is stored in env var
$ENVVARNAME

Environment files

Generally populated from the /etc/skel file. Users can edit these files after they are in their user account.
The first file found in the following order is ran, and the rest are ignored:
- .bash_profile
- .bash_login
- .profile
  .bashrc is run from a file in the preceding list. It is also always run when there is a non-interactive shell started

Global files

Global files:

/etc/profile
/etc/profile.d files
/etc/bash or /etc/bash.bashrc file (depends on distro)

Do not change global files. You can create a custom env file with an .sh extension and place it in /etc/profile.d. Files in this directory are run during bash login.

Set default text editor

Ubuntu uses nano by default, change it to vim:

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

Uncomment some lines in the global bash.bashrc file:

sudo vim /etc/bash.bashrc 

# opened file - uncomment if lines
# 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 set-hostname mylittlecloudbox

Set timezone

This is important for scheduling tasks and the timestamps for logs under /var/log:

# view 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)             # current tz
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

# get list of available timezones
timedatectl list-timezones

# set new timezone
sudo timedatectl set-timezone America/New_York

# verify
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 config files. The personal config files are hidden in /home/:

`.bashrc`

Runs every time you open a bash terminal.

You can source .profile from this file. In .profile, you can load other dot config files to keep your env clean.

# if you have a terminal prompt, load profile
[ -n "$PS1" ] && source ~/.profile

`.profile`

Load OS-specific settings or other dot files:

# if file exists and is readable, source it
for file in ~/.{exports,aliases,functions,extra}; do
    [ -r "$file" ] && source "$file"
done
unset file

`.aliases`

File dedicated to aliases only:

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

`.exports`

Set environment variables:

# set GOPATH
export GOPATH="$HOME/go-workspace"

`.vimrc`

vim configuration file. For more info, open vim and enter :help vimrc-intro:

`.gitignore`

Ignore files from git tracking.

Prompt Statement (PS)

Add customizations to .bashrc to make them permanent.

PS1

Default interactive prompt. See this phoenixNap page for a complete list of options.

PS2

Continuation interactive prompt. This is the prompt displayed when you enter a multi-line command:

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

PS3

For select command prompts, it lets you replace the #?. I don’t see a good reason to use this often.

Read this Geek Stuff article for an example.

PS4

Customize the debug mode (set -x) output for shell scripts. By default, it outputs ++ beside each line of the script. You can customize it to output the script name and line number:

# default PS4
+ echo 'PS4 demo script'
PS4 demo script
+ ls -l /etc
+ wc -l
229
+ du -sh /home/linuxuser
1.4G	/home/linuxuser

# custom PS4: export PS4='Line: $LINENO++ '
Line: 7++ echo 'PS4 demo script'
PS4 demo script
Line: 8++ ls -l /etc
Line: 8++ wc -l
229
Line: 9++ du -sh /home/linuxuser
1.4G	/home/linuxuser

PROMPT_COMMAND

Executed right before displaying PS1:

export PROMPT_COMMAND="date +%k:%m:%S"
11:12:35
# next command
ls -1
find-files
...
11:12:43

# display on same line as PS1
export PROMPT_COMMAND="echo -n [$(date +%k:%m:%S)]"k:%m:%S)]"
[11:12:35]user@machine:~$

vim

There are two modes: “normal” and “insert”.

Pres ESC twice to return to normal mode

Editing

Command	Description
`i`	insert mode
`w`	write
`u`	undo
`wq`	write and quit
`q`!	quit without saving

Command	Description
`h`	Move left
`j`	Move down
`k`	Move up
`l`	Move right
`w`	Move to the beginning of the next word
`3w`	move to the 3rd word to the right
`3wd`	delete the 3 words to the right
`b`	Move to the beginning of the previous word
`3b`	move to the 3rd word to the left
`e`	Move to the end of the current word
`0`	Move to the beginning of the line
`$`	Move to the end of the line
`gg`	Go to the first line of the file
`G`	Go to the last line of the file
`Ctrl + u`	Move up half a screen
`Ctrl + d`	Move down half a screen
`(`	next sentence beginning
`)`	prev sentence beginning

Editing

Command	Description
`i`	Insert mode at the cursor
`I`	Insert mode at the beginning of the line
`a`	Append mode after the cursor
`A`	Append mode at the end of the line
`o`	Open a new line below the current line
`O`	Open a new line above the current line
`r`	replace current char with next char you enter
`x`	Delete the character under the cursor
`X`	Delete the character before the cursor
`dd`	Delete the current line
`99dd`	Delete 99 lines
`dw`	Delete from the cursor to the end of the word
`3wd`	Delete the 3 words to the right
`db`	Delete word to the left
`3db`	Delete the 3 words to the left
`d$`	Delete from the cursor to the end of the line
`d0`	Delete from the cursor to the beginning of the line
`das`	Delete current sentence
`yy`	Copy (yank) the current line
`3yy`	copy three lines, starting from the line where the cursor is positioned.
`yw`	Copy (yank) the current word
`yiw`	copy the current word.
`y$`	Copy (yank) to the end of the line
`y%`	copy to the matching character. By default supported pairs are (), {}, and []. Useful to copy text between matching brackets.
`y^`	copy everything from the cursor to the start of the line.
`p`	Paste after the cursor
`5p`	paste 5 times
`P`	Paste before the cursor
`u`	Undo
`Ctrl + r`	Redo

Visual Mode

Command	Description
`v`	Start visual mode
`V`	Start visual line mode
`vjjj`	highlight current line and 3 lines below (number of js)
`vjjjyy`	hightlight and copy three lines
`Ctrl + v`	Start visual block mode
`y`	Yank (copy) the selected text
`d`	Delete the selected text
`>`	Indent the selected text
`<`	Un-indent the selected text

Search and Replace

Command	Description
`/pattern`	Search for pattern
`?pattern`	Search backward for pattern
`n`	Repeat the search in the same direction
`N`	Repeat the search in the opposite direction
`:%s/old/new/g`	Replace all occurrences of old with new in the entire file
`:%s/old/new/gc`	Replace all occurrences with confirmation

Working with Multiple Files

Command	Description
`:e filename`	Open a file
`:w`	Save the current file
`:w filename`	Save as filename
`:q`	Quit Vim
`:wq`	Save and quit
`:q!`	Quit without saving
`:bn`	Go to the next buffer
`:bp`	Go to the previous buffer
`:bd`	Delete a buffer

Useful Commands

Command	Description
`:set nu`	Show line numbers
`:set nonu`	Hide line numbers
`:syntax on`	Enable syntax highlighting
`:syntax off`	Disable syntax highlighting
`:set paste`	Enable paste mode
`:set nopaste`	Disable paste mode
`:set tabstop=4`	Set tab width to 4 spaces
`:set expandtab`	Convert tabs to spaces
`:set shiftwidth=4`	Set indentation width to 4 spaces

Exiting Vim

Command	Description
`:w`	Save the file
`:q`	Quit Vim
`:wq` or `ZZ`	Save and quit
`:q!`	Quit without saving

.`vimrc`

Config file for vim:

In /home/.vimrc, but there is also a system-wide /etc/vimrc

# Start vim without reading .vimrc
vim -u NONE

Environment

Environment setup

Environment variables

Environment files

Global files

Set default text editor

Enable bash completion globally

Change hostname

Set timezone

dot files

.bashrc

.profile

.aliases

.exports

.vimrc

.gitignore

Prompt Statement (PS)

PS1

PS2

PS3

PS4

PROMPT_COMMAND

vim

Editing

Basic Navigation

Editing

Visual Mode

Search and Replace

Working with Multiple Files

Useful Commands

Exiting Vim

.vimrc

`.bashrc`

`.profile`

`.aliases`

`.exports`

`.vimrc`

`.gitignore`

.`vimrc`