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Comparative character writing in UNIX Shell

-eq equals;-ne does not equal

-gt is greater than;-lt is less than

-le less than or equal to;-ge greater than or equal to

-z empty string;-n non-empty string

= two characters are equal;! = two characters are not equal

No matter what programming language is inseparable from conditional judgment. SHELL is no exception.

The general format is as follows:

If list thendo something hereelif list thendo another thing hereelsedo something else herefi is basically the same as any other scripting language. There's not much difference. But it's worth noting that. [] the judgment of the conditions inside. The explanation is as follows: 1 string judgment

Str1 = str2

True str1! = str2 when two strings have the same content and length

True-n str1 when strings str1 and str2 are not equal

True (string is not empty)-z str1 when the length of the string is greater than 0

True (empty string) str1 when string length is 0

True when string str1 is not empty

The judgment of 2 numbers

Int1-eq int2

The equality of two numbers is true int1-ne int2

Two numbers are not equal to true int1-gt int2

True int1-ge int2 if int1 is greater than int2

Int1 greater than or equal to int2 is true int1-lt int2

True int1-le int2 if int1 is less than int2

True that int1 is less than or equal to int2

3 if judgment condition statements related to files

-r file

User readable as true-w file

User can write as true-x file

User executable is true-f file

File is regular file is true-d file

File is directory is true-c file

The file is a character and the special file is true-b file

The file is a block and the special file is true-s file

True if the file size is non-0-t file

True when the device specified by the file descriptor (default is 1) is a terminal

4 complex logic judgment

-an and-o or! Non

Although the syntax is simple, it can implement powerful functions or execution logic when used in SHELL.

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