Judging usage in the shell

Source: Internet
Author: User

Test structure:

The test command can be used to test the true and false of the expression condition, and returns0,false, which is not 0;


Test expression

    #expression是一个表达式, the expression can be compared by numbers, strings, text and file attributes, and can be added to various arithmetic, string, text operators, etc.;


#其中 "[" is the command to start the test, but requires a "]" to be paired with it after expression, paying special attention to the spaces before "[" and "]" are necessary.

The #该方式经常与if, case and while statements are used as the judging conditions of the process control statements;

A comparison between integers:

comparators: eq, GT, Lt//equal, greater than, less than

Test "NUM1"-eq "num2"

["Num1"-eq "num2"]

The comparer cannot be used for comparisons between floating-point numbers, remember

A comparison between strings:

String to test whether string is not NULL,

-N string to test whether the string is not empty

-Z String to test if string is empty

Operators for file operations:

Judging usage in the shell

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