Shell Common Test commands

Pre-defined variables:

Predefined variables are a class of special variables that are predefined by bash programs, and users can only use predefined variables, not create new predefined variables, or assign values directly to predefined variables. The predefined variable is represented by a "$" match and another symbol combination.

$#: Indicates the number of positional parameters in the command.

$*: Represents the contents of all positional parameters.

$?: Represents the return state after the previous command was executed, with a return value of 0 indicating that the execution is correct, and any non-0 value indicates an exception occurred.

$ A: Represents the name of the currently executing script or program.

File test:

The-D test is a catalog (directory).

-e tests whether the directory or file exists (Exist).

The-f test is a file.

-R to test whether the current user has permission to read (read).

-W tests whether the current user has permission to write (write).

-X tests whether there are execute permissions (excute).

Attached:-D parameter Use example: #[-d/tmp/]

#echo $? View the return value of the previous command, 0 indicates that the TMP directory exists.

#[-d/tmp/] && echo "yes"//If the TMP directory is present, print YES on the screen.

Integer value comparison:

-eq 1th number Equals (Equal) 2nd

-ne 1th Number Not equal to (not Equal) 2nd number

-GT 1th number greater than (Greater Than) 2nd number

-LT 1th number less than (Lesser Than) 2nd number

-le 1th number less than or equal to (Lesser or Equal) 2nd number

-ge 1th number greater than or equal to (Greater or Equal) 2nd number

attached:-GT parameters Use Example: #[6-gt 5] && echo "Too many"

string comparison:

= The 1th string is the same as the 2nd string.

! = The 1th string is not the same as the 2nd string, where "! "means to take the opposite."

-Z Checks if the string is empty (Zero), and the variable that is not defined or given a null value is treated as an empty string.

Logic test:

and &&: logical And, meaning "and", only when the two conditions are true, the return value of the entire test command is 0. When testing with the test command, && can be changed to "-a".

or | | Logical OR, meaning "or", as long as there is one of the two conditions, the return value of the entire test command is 0 (the result is set). When testing with the test command, the "| |" Can be changed to "-O".

Non -! : Logical no, means "no", only if the specified condition is not true, the return value of the entire test command is 0 (the result is set).

　　　　　　　

Shell Common Test commands