Testing

The testing commands shown here are usually used along with if/else control flow statements. Both the string testing function ([[) and the arithmetic testing function ((() return 0 if the test evaluates to a true value, or 1 if the test evaluates to false. This is due to the 0 exit code of commands indicating success, and it is different from other programming languages you might know that typically evaluate a zero value as false. There is no native boolean data type in Bash; the integers 0 and 1 are used in boolean contexts like this one. Sometimes, the variables true and false are initialized and used throughout a script.

Testing operators

Here are some basic boolean operators that you can use to construct statements in Bash – essentially, what you’re used to from other languages:

• ! – not (negation)
• && – and
• || – or

These operators can be used with both string and arithmetic test types:

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