Environment Management

Shell is outer layer

Env variables

written in upper case

List environment variables env

PWD , OLDPWD,

Create new env variable

export VAR="VALUE"

Environment variable PATH

echo $PATH

/home/azureuser/.local/bin:/home/azureuser/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin

higher priority for left ones

Modify the path

PATH="${PATH}:/opt/app/bin"

Find binaries

which <binary-name>

Environment variable SHELL

echo $SHELL, chsh -s /bin/bash, cat /etc/shells,

Persistant env variables

~/.bashrc, ~/.bash_profile, ~/.profile,

1. interactive login shell (ssh/tty)
2. interactive non login shell (terminal on gui/shell insde interactive shell)
3. non interactive login shell ()
4. non interactive non login shell (script.sh)

Bash startup files

login into interactive login shell

• /etc/profile
  • ~/.bash_profile
  • ~/.bash_login
  • ~/.profile

Login into interactive non-login shell

• ~/.bashrc

Alias

alias gohome='cd ~'

Configuring shell

enable feature set -[feature]

disable feature set +[feature]

set -x # enable debug feature in shell

set +x #disable debug feature in shell

List of features available at https://www.gnu.org/software/bash/manual/html_node/The-Set-Builtin.html

enable configuration option

shopt -s [optname]

disable configuration option

shopt -u [optname]

https://www.gnu.org/software/bash/manual/html_node/The-shopt-Builtin.html

Bash Prompt customize

PS1 variable

In PS1

Put this PS1 value in .bashrc

how color works in bash

echo “${TERM}“

toe or toe -a

infocmp

tput command

tput clear, tput cup 5 20, tput bold, tput sgr0, tput smul, tput setaf 4, tput setab 5,

to list colors

for i in {0..15}; do echo "$(tput setab ${i}) color: ${i}$(tput sgr0)"; done

tput lines, tput cols, tput colors,

https://www.gnu.org/software/bash/manual/html_node/Controlling-the-Prompt.html

PS1

PS1='\n🖥️ \h | 👤 \u | 🕒 \A\n📁 $(pwd | sed "s|^/||; s|/| ➤ |g")\n\$ '

PS1='\n👤\u@🖥️\h:📁$(pwd | sed "s|^/||; s|/| ➤ |g") |  (🕒\A)\n\$ '

Shell expansions

ls * , ls ?.txt, ls ~,

Variable expansion

$HOME, ${HOME},

Print part of variable from starting point and length

${VARIABLE:start:length}

Print variable with replacing path

${VARIABLE/pattern/replace}

cat $PWD/*.txt will expand variable and regex

single quotes will not expand anything

double quotes will expand variables but not the eregex

Escaping in shell

brace expansion

echo data.{csv,txt} is equal to

no qutes for brace expansion