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

#-------------------------------
# TEXT
i # insert mode
w # write
u # undo
wq # write and quit
q! # quit without saving

a # begin typing after the cursor
o # insert new line below and enter text
O # insert new line on current line enter text - existing line moves down
x # delete current character
r # replace current char with next char you enter
dd # delete lines
dw # delete word to the right
3wd # delete the 3 words to the right
db # delete word to the left
3bd # delete the 3 words to the left
99dd # delete 99 lines
d0 # delete to the beginning of the sentence
d$ # delete to the end of the sentence
das # delete current sentence

33dd # delete 33 lines
u # undo

#-------------------------------
# NAVIGATION
gg # go to top of file
G # go to bottom of file
w # skip to next wordj
dw # delete word to the rightkk
3w # move to the 3rd word to the right
3wd # delete the 3 words to the right
b # skip to previous word
db # delete word to the left
3b # move to the 3rd word to the left
3bd # delete the 3 words to the left
( # next sentence beginning
) # prev sentence beginning

#-------------------------------
# SEARCHING
/<pattern> # search file for pattern
n # after search, step forward through <pattern> occurrences
N # after search, step backward through <pattern> occurrences

#-------------------------------
# CUT and PASTE
yy # yank text (copy)
p # after delete, paste the
5p # paste 5 times
yy # copy the current line, including the newline character.
3yy # copy three lines, starting from the line where the cursor is positioned.
y$ # copy everything from the cursor to the end of the line.
y^ # copy everything from the cursor to the start of the line.
yw # copy to the start of the next word.
yiw # copy the current word.
y% # copy to the matching character. By default supported pairs are (), {}, and []. Useful to copy text between matching brackets.

#-------------------------------
# VISUAL MODE
v # highlight current line
V # visual mode, select text by line
CTRL + V # visual mode, select text by char
vjjj # highlight current line and 3 lines below (number of js)
vjjjyy # hightlight and copy three lines

.`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