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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

Path Purpose
/bin Essential Binaries, available always
/sbin Essential root binaries, available for root always
/usr/bin Non-essential, available for all users, shared with other computers
/usr/sbin Non-essential, for root users, shared with other computers
/usr/local/bin Non-essential, for all user on this hosts
/usr/local/sbin Non-essential, for all root users on the host

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

Option Use
\u Username
\h hostname
\H FQDN
\w Full Path
\W Current Directory
\t time in 24H
\@ time in 12H

Put this PS1 value in .bashrc

how color works in bash

echo ā€œ${TERM}ā€œ

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='\nšŸ–„ļø \h | šŸ‘¤ \u | šŸ•’ \A\nšŸ“ $(pwd | sed "s|^/||; s|/| āž¤ |g")\n\$ '

PS1='\nšŸ‘¤\u@šŸ–„ļø\h:šŸ“$(pwd | sed "s|^/||; s|/| āž¤ |g") |  (šŸ•’\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