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The case statement is equivalent to a multi-branch if/elif/else statement, and using case makes the script look simpler and neat. In the case statement, the program compares the obtained values with the conditions in the case expression one by one, executes the corresponding statement if it matches, and stops execution when it encounters a double semicolon (;;). If no match is found, execute the statement that follows *), which is equivalent to the default function in other languages.

Basic grammar

Case "var" in

Value 1)

Statement

Value 2)

Statement

Value n)

Statement

*)

Statement

Esac

The last branch statement, that is, before esac, can omit the double semicolon

Case example

[root@localhost Test] # cat case.sh

#! / bin/bash

Astatine 1

Case "${a}" in

1)

Echo "input number is 1"

2)

Echo "input number is 2"

3)

Echo "input number is 3"

*)

Echo "case default value"

Esac

[root@localhost Test] # bash case.sh 1

Input number is 1 # matching condition 1

[root@localhost Test] # bash case.sh 3

Input number is 3 # matching condition 3

[root@localhost Test] # bash case.sh a

Case default value # does not match the condition

The same effect can be achieved by using if statements.

[root@localhost Test] # cat caseif.sh

#! / bin/bash

Astatine 1

If [${a}-eq 1]

Then

Echo "input number is 1"

Elif [${a}-eq 2]

Then

Echo "input number is 2"

Elif [${a}-eq 3]

Then

Echo "input number is 3"

Else

Echo "case default value"

Fi

[root@localhost Test] # bash caseif.sh 1

Input number is 1

[root@localhost Test] # bash caseif.sh 3

Input number is 3

[root@localhost Test] # bash caseif.sh a

Caseif.sh: line 3: [: a: expect an integer expression

Caseif.sh: line 6: [: a: expect an integer expression

Caseif.sh: line 9: [: a: expect an integer expression

Case default value

Summary of case statements

1. The case statement is more suitable for a fixed set of numbers or strings with fewer variables.

2. Case is often used to write startup scripts for services, etc.

3. If takes values for judgment and comparison, and its application is wider than that of case, and most case statements can be replaced by if.

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