Conditions in the shell determine if and test

(a) Conditions to determine if the meaning of-Z to-D

[-A file] is true if file exists.

[-B file] True if file exists and is a block special file.

[-C file] True if file exists and is a special file of a word .

　　[-D file] True if file exists and is a directory .

　　[-E File] True if file exists .

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

[-G file] True if file exists and Sgid has been set.

[-H file] True if file exists and is a symbolic connection.

[-K file] True if file exists and the sticky bit has been set.

[-P file] True if file exists and is a pipe.

　　[-R File] True if file exists and is readable.

　　[-S file] True if file exists and the size is not 0.

[-T FD] true if the file descriptor FD is open and points to a terminal.

[-u file] True if file exists and suid is set.

　　[-W file] True if file exists and is writable.

　　[-X file] True if file exists and is executable .

[-o file] True if file exists and is a valid user ID.

[-G file] True if file exists and is a valid user group.

[-L file] True if file exists and is a symbolic connection.

[-S file] True if file exists and is a socket.

(ii) Condition testing

　　Use the "test" or "[]" command :

If Test-f file.c

Then ...

Fi

Or:

If [-F file.c]

Then ...

Fi

　　Note : When you use square brackets "[]" to test the condition, the square brackets leave a space between the test conditions.

　　

Test condition Classification:

　　　　string comparison class \ Arithmetic comparison class \ file-related condition test class

1. String comparison class:

string1 = string2 If two strings are the same , the result is true

String1! = string2 If the two strings are different, the result is true

　　- N String If the string is not empty , the result is true

　　- Z String If the string is empty , the result is true

　　note that when comparing equal or unequal, both sides of the =/!= must have a space character separated from the two strings to be compared.

　　2. Arithmetic Comparison class:

Expression1–eq expression2 #如果两个表达式equal , the result is true Expression1–ne expression2 #如果两个表达式range , The result is true expression1–gt expression2 #如果前一个表达式 is greater than the last expression, the result is true Expression1–ge expression2 #如果前一个表达式greater than or equal to After an expression, the result is true expression1–lt expression2 #如果前一个表达式less than the last expression, the result is true Expression1–le expression2 #如果前一个表达式 Less than or equal to the latter expression, the result is true! Expression #取表达式的非, which is false , the result is true

3. file Comparison class:

[File1-nt FILE2] If FILE2 is older than FILE1, or if FILE1 exists and FILE2 does not true.

[File1-ot FILE2] If FILE1 is older than FILE2, or FILE2 exists and FILE1 does not exist, it is true.

[File1-ef FILE2] True if FILE1 and FILE2 point to the same device and node number.

　　

　　

Conditions in the shell determine if and test