Shell Script---syntax chapter

1. Condition test

1) test

2) [

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Test command:

[-D dir]: true if Dir exists and is a directory

[-F file]: True if file exists and is a normal file

[-Z string]: True if the length of the string is zero

[-N string]: True if the length of a STRING is nonzero

[STRING1 = STRING2]: True if two strings are the same

[STRING1! = STRING2]: True if the string is not the same

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3) If statement

If the two commands are written in the same line, they need to be separated from each other, and a single command on one line does not need to be written;

But this command is not finished, the shell will automatically continue, the next line is followed by then as a command processing. As with the command, be aware that the command and parameters must be separated by a space. If the parameter of the IF command consists of a sub-command, if the subcommand's exit status is 0 (true), then the subcommands that follow then are executed, and if exit status is not 0 (false), then the subcommands after elif, else, or fi are executed. A subcommand after an if is usually a test command, but it can also be another command. The shell script does not have {} brackets, so use fi to indicate the end of the IF statement block.

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When the condition is established, use: No.

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4) Case statement

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5) For Loop statement

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2. Functions

There are two ways to get the return value of a function:

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3. Arrays

Shell scripts support only one-dimensional arrays, only sequential arrays are supported, associative arrays are not supported

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Shell Script---syntax chapter