Question

Use of case structure and use of break in shell scripting

Answer 1

Use of case structure and use of break in shell scripting

Case structure

Shell supports case...esac statement which handles exactly this situation, and it does so more efficiently than repeated if...elif statements.

• The case statement allows you to easily check pattern (conditions) and then process a command-line if that condition evaluates to true.
• In other words the $variable-name is compared against the patterns until a match is found.
• *) acts as default and it is executed if no match is found.
• The pattern can include wildcards.
• You must include ;; at the end of each command-n. The shell executes all the statements up to the two semicolons that are next to each other.
• The esac is always required to indicate end of case statement.

Syntax

case word in    pattern1)       Statement(s) to be executed if pattern1 matches       ;;    pattern2)       Statement(s) to be executed if pattern2 matches       ;;    pattern3)       Statement(s) to be executed if pattern3 matches       ;;    *)      Default condition to be executed      ;; esac

Example

echo "Enter a number"  read num  case $num in  [0-9])  echo “you have entered a single digit number”  ;;  [1-9][1-9])  echo “you have entered a two-digit number”  ;;  [1-9][1-9][1-9])  echo “you have entered a three-digit number”  ;;  *)  echo “your entry does not match any of the conditions”  ;;  esac

Output

break statement

break command is used to terminate the execution of for loop, while loop and until loop. It can also take one parameter i.e.[N]. Here n is the number of nested loops to break. The default number is 1.

Example

for i in `seq 1 10` do if(($i ==5)) then break fi echo $i done

Output

 

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