Linux in a Nutshell, Fourth Edition

Name

test

Synopsis

                  test 
                  expression 
[expression]

Evaluate an expression and, if its value is true, return a zero exit status; otherwise, return a nonzero exit status. In shell scripts, you can use the alternate form [ expression ]. This command is generally used with conditional constructs in shell programs. Also exists as a built-in in most shells.

File testers

The syntax for all of these options is test option file. If the specified file does not exist, they return false. Otherwise, they test the file as specified in the option description.

-b

Is the file block special?

-c

Is the file character special?

-d

Is the file a directory?

-e

Does the file exist?

-f

Is the file a regular file?

-g

Does the file have the set-group-ID bit set?

-k

Does the file have the sticky bit set?

-L

Is the file a symbolic link?

-p

Is the file a named pipe?

-r

Is the file readable by the current user?

-s

Is the file nonempty?

-S

Is the file a socket?

-t [file-descriptor]

Is the file associated with file-descriptor (or 1, standard output, by default) connected to a terminal?

-u

Does the file have the set-user-ID bit set?

-w

Is the file writable by the current user?

-x

Is the file executable?

-O

Is the file owned by the process’s effective user ID?

-G

Is the file owned by the process’s effective group ID?

File comparisons

The syntax for file comparisons is test file1 option file2. A string by itself, without options, returns true if it’s at least one character long.

-nt

Is file1 newer than file2? Check modification ...