Bash Cheat Sheet 2023 - Master Bash Scripting

Bash: CheetSheet

What is Bash ?

Bash is a powerful programming language, one perfectly designed for use on the command line and in shell scripts. Bash can be used to automate software development tasks such as code compilation, debugging source code, change management and software testing.

In this article we will discuss about common Bash Commands and their usase-

Bash Shortcut Commands

BASH Basic Commands

BASH FILE COMMANDS

BASH DIRECTORY COMMANDS

BASH SSH, SYSTEM INFO & NETWORK COMMANDS

BASH VARIABLES

BASH FUNCTIONS

The function refers to passed arguments by position (as if they were positional parameters), that is, $1,$2, and so forth.

$@ is equal to "$1" "$2"... "$N", where N is the number of positional parameters. $# holds the number of positional parameters.

function functname() {
  shell commands
}
unset -f functname  # deletes a function definition
declare -f          # displays all defined functions in your login session

BASH FLOW CONTROLS

BASH STRINGS

BASH FILES

BASH NUMBERS

if condition
then
statements
[elif condition
then statements...]
[else
statements]
fi

for x in {1..10}
do
statements
done

for name [in list]
do
statements that can use $name
done

for (( initialisation ; ending condition ; update ))
do
statements...
done

case expression in
pattern1 )
    statements ;;
pattern2 )
    statements ;;
esac

select name [in list]
do
statements that can use $name
done

while condition; do
statements
done

until condition; do
statements
done

BASH COMMAND-LINE PROCESSING CYCLE

The default order for command lookup is functions, followed by built-ins, with scripts and executables last. There are three built-ins that you can use to override this order: command, builtin and enable.

BASH INPUT/OUTPUT REDIRECTORS

BASH PROCESS HANDLING

To suspend a job, type CTRL+Z while it is running. You can also suspend a job with CTRL+Y. This is slightly different from CTRL+Z in that the process is only stopped when it attempts to read input from terminal. Of course, to interrupt a job, type CTRL+C.

BASH TIPS & TRICKS

• Set an alias

    cd; nano .bash_profile

alias gentlenode='ssh admin@gentlenode.com -p 3404' # add your alias in .bash_profile

• To quickly go to a specific directory

    cd; nano .bashrc
    > shopt -s cdable_vars
    > export websites="/Users/mac/Documents/websites"

    source .bashrc
    cd $websites

DEBUGGING SHELL PROGRAMS IN BASH

• trap 'echo $varname' EXIT - useful when you want to print out the values of variables at the point that your script exits|

  function errtrap {
      es=$?
      echo "ERROR line $1: Command exited with status $es."
  }
  

• trap 'errtrap $LINENO' ERR - is run whenever a command in the surrounding script or function exits with non-zero status

  function dbgtrap {
      echo "badvar is $badvar"
  }
  

• trap dbgtrap DEBUG - causes the trap code to be executed before every statement in a function or script ...section of code in which the problem occurs...

• trap - DEBUG - turn off the DEBUG trap

      function returntrap {
      echo "A return occurred"
  }
  

• trap returntrap RETURN - is executed each time a shell function or a script executed with the . or source commands finishes executing

BASH TEXT COLORS AND BACKGROUNDS

• note: \e or \x1B also work instead of \033

• Color_Off='\033[0m' - Text Reset

• Regular Colors

  Black='\033[0;30m'  # Black
  Red='\033[0;31m'    # Red
  Green='\033[0;32m'  # Green
  Yellow='\033[0;33m' # Yellow
  Blue='\033[0;34m'   # Blue
  Purple='\033[0;35m' # Purple
  Cyan='\033[0;36m'   # Cyan
  White='\033[0;97m'  # White
  

• Additional colors

  LGrey='\033[0;37m'  # Ligth Gray
  DGrey='\033[0;90m'  # Dark Gray
  LRed='\033[0;91m'   # Ligth Red
  LGreen='\033[0;92m' # Ligth Green
  LYellow='\033[0;93m'# Ligth Yellow
  LBlue='\033[0;94m'  # Ligth Blue
  LPurple='\033[0;95m'# Light Purple
  LCyan='\033[0;96m'  # Ligth Cyan
  

• Bold

  BBlack='\033[1;30m' # Black
  BRed='\033[1;31m'   # Red
  BGreen='\033[1;32m' # Green
  BYellow='\033[1;33m'# Yellow
  BBlue='\033[1;34m'  # Blue
  BPurple='\033[1;35m'# Purple
  BCyan='\033[1;36m'  # Cyan
  BWhite='\033[1;37m' # White
  

• Underline

  UBlack='\033[4;30m' # Black
  URed='\033[4;31m'   # Red
  UGreen='\033[4;32m' # Green
  UYellow='\033[4;33m'# Yellow
  UBlue='\033[4;34m'  # Blue
  UPurple='\033[4;35m'# Purple
  UCyan='\033[4;36m'  # Cyan
  UWhite='\033[4;37m' # White
  

• Background

  On_Black='\033[40m' # Black
  On_Red='\033[41m'   # Red
  On_Green='\033[42m' # Green
  On_Yellow='\033[43m'# Yellow
  On_Blue='\033[44m'  # Blue
  On_Purple='\033[45m'# Purple
  On_Cyan='\033[46m'  # Cyan
  On_White='\033[47m' # White
  

• Example of usage

  echo -e "${Green}This is GREEN text${Color_Off} and normal text"
  echo -e "${Red}${On_White}This is Red test on White background${Color_Off}" 
  

  printf "${Red} This is red \n"
  

option -e is mandatory, it enable interpretation of backslash escapes