CASE statements are similir to ELIF statements, use case if elif statements are more than 3.

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

Exactly how you use fi to end if statements, you close a case statement with esac (which is the alphabetic opposite of case, case spelled backwards).

;; marks the end of a statement.

Example:

echo -n "give me a domain: "
read domain

case $domain in
  "google.com" )
    echo "Google, wow!" ;;
  "twitter.com" )
    echo "Twitter -_-" ;;
  "udemy.com" ) 
    echo "Udemy, YES!" ;;
  "aamnah.com" )
    echo "Aamnah.com, brilliant. Let's PING!"
    ping -c3 aamnah.com ;;
esac

case "$1" in
  start) 
    /usr/sbin/sshd
    ;;
  stop)
    kill $(cat /var/run/sshd.pid)
    ;;
esac

In the example above if $1 is equal to start then /usr/sbin/sshd is executed. If $1 is equal to stop then the kill command is executed. If $1 matches neither start nor stop then nothing happens and the script continues after the statement.

Note: case statements (start and stop in the example above) are case-sensitive.

case "$1" in
  start) 
    /usr/sbin/sshd
    ;;
  stop)
    kill $(cat /var/run/sshd.pid)
    ;;
  *)
    echo "Usage start|stop" 
    exit 1
    ;;
esac

In this example, anything other than start or stop will show usage instructions.

wildcards *

*)
  echo "Usage start|stop" 
  exit 1
  ;;

is the same as

*)
  echo "Usage start|stop" ; exit 1
  ;;

check multiple conditions |

You can use pipe | to seperate multiple case statement conditions/options. | servers as OR

case "$1" in
  start|START) 
    /usr/sbin/sshd
    ;;
  stop|STOP)
    kill $(cat /var/run/sshd.pid)
    ;;
  *)
    echo "Usage start|stop" 
    exit 1
    ;;
esac

Character classes []

Character classes are simply a list of characters between brackets []. Like so:

[yY][nN]

A character class matches exactly one character, and a match occurs for any of the including characters in the brackets.

[yY][eE][sS]

will check for all case-sensitive possibilities of yes. yes, Yes, yEs, yeS, YEs, yES, YeS, and so on.. Here’s a code example:

read -p "Enter y or n: " ANSWER

case "$ANSWER" in
  [yY]|[yY][eE][sS] )
    echo "You answered yes." ;;
  [nN]|[nN][oO] )
    echo "You answered no." ;;
  * )
    echo "Invalid answer." ;;
esac
  • https://www.udemy.com/shell-scripting-linux/learn/#/lecture/3351956