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The structure of the if statement

2025-01-19 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Servers >

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Shulou(Shulou.com)06/02 Report--

The structure of the if statement is in the shell script, and the if statement is the most commonly used flow control method. It is used to judge the result according to specific conditions and perform different operations (if. So.). According to different complexity, the choice structure of if sentence can be divided into three basic types, which are suitable for different applications. 1. A single-branch if statement executes the corresponding code only when the condition is established, otherwise no action is performed. Format: if conditional test operation then (conditions will be executed only) command sequence fi ending process: if followed by conditional judgment, only two results are "true or not". If the condition judgment is established, the command sequence after the then will be executed, and if it is not established, the direct fi termination will not be executed.

two。 The double-branch if structure requires that different operation formats be executed according to the two cases of "condition is established" and "condition is not": ifthen command sequence 1 (condition is established) else command sequence 2 (condition is not valid) fi flow: if judges whether the condition is true, execute "then" command 1 when the condition is established, and execute "else" command sequence 2 if the condition is not true.

3. Multi-branch if structure because the if statement can be established according to the test results, it is not established to perform operations separately, so it can be used in nesting and make multiple judgments. Format: if condition test operation 1then command sequence 1elif condition test operation 2then command sequence 2else command sequence 3fi process: first determine whether the if condition is true, if not, do not rush to exit, and then to determine whether the "elif" condition is true, if it is established, execute "then" command sequence 2, if it is not established, execute "else" command sequence 3 by default.

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