- condition evaluation command
test evaluates the expression expression and if its value is true, sets a 0 (TRUE) exit status; otherwise, a non-zero (FALSE) exit status is set; test also sets a non-zero exit status if there are no arguments. When permissions are tested, the effective user ID of the process is used.
All operators, flags, and brackets (brackets used as shown in the second SYNOPSIS line) must be separate arguments to test. Normally these items are separated by spaces.
The following primitives are used to construct expression:
True if filename exists and is readable.
True if filename exists and is writable.
True if filename exists and is executable.
True if filename exists and is a regular file.
True if filename exists and is a directory.
True if filename exists and is a character special file.
True if filename exists and is a block special file.
True if filename exists and is a named pipe (FIFO).
True if filename exists and its set-user-ID bit is set.
True if filename exists and its set-group-ID bit is set.
True if filename exists and its sticky bit is set.
True if filename exists and has a size greater than 0.
True if the open file whose file descriptor number is fildes (1 by default) is associated with a terminal device.
True if the length of string s1 is 0.
True if the length of the string s1 is non-zero.
True if strings s1 and s2 are identical.
True if strings s1 and s2 are not identical.
True if s1 is not the null string.
True if the integers n1 and n2 are algebraically equal. Any of the comparisons -ne, -gt, -ge, -lt, and -le may be used in place of -eq.
These primaries may be combined with the following operators:
Unary negation operator.
Binary and operator.
Binary or operator (-a has higher precedence than -o).
Parentheses for grouping. Notice also that parentheses are meaningful to the shell and, therefore, must be quoted.
See attributes(5) for descriptions of the following attributes:
If you test a file you own (the -r , -w , or -x tests), but the permission tested does not have the owner bit set, a non-zero (false) exit status will be returned even though the file may have the group or other bit set for that permission. The correct exit status will be set if you are super-user.
The = and != operators have a higher precedence than the -r through -n operators, and = and != always expect arguments; therefore, = and != cannot be used with the -r through -n operators.
If more than one argument follows the -r through -n operators, only the first argument is examined; the others are ignored, unless a -a or a -o is the second argument.