Test (Unix)

From Wikipedia, the free encyclopedia

The correct title of this article is test. The initial letter is shown capitalized due to technical restrictions.

test is a Unix command that evaluates conditional expressions.

1 Syntax
2 Description
3 Functions
4 Exit Status
5 Examples
6 External links
7 See also

[edit] Syntax

test Expression or [ Expression ]

[edit] Description

The test command evaluates the expression parameter, and if the expression value is true, it returns a zero (True) exit value. Otherwise, the test command returns a nonzero (false) exit value. The test command also returns a nonzero exit value if there are no parameters.

Notes: 1. In the second form of the command, the [ ] (brackets) must be surrounded by blank spaces. 2. You must test explicitly for file names in the C shell. File-name substitution (globbing) causes the shell script to exit.

Functions and operators are treated as separate parameters by the test command. The expression parameter refers to a statement that is checked for a true or false condition.

[edit] Functions

The following functions are used to construct this parameter:

-b Filename -- Returns a True exit value if the specified FileName exists
   and is a block special file.

Note: All remaining functions return true if the object (file or string) exists, and the condition specified is true.

-c FileName -- Filename is a character special file.
-d FileName -- FileName is a directory.
-e FileName -- FileName exists.
-f FileName -- FileName is a regular file.
-g FileName -- FileName's Set Group ID bit is set.
-h FileName -- FileName is a symbolic link.
-k FileName -- FileName's sticky bit is set.
-L FileName -- FileName is a symbolic link.
-p FileName -- FileName is a named pipe (FIFO).
-r FileName -- FileName is readable by the current process.
-s FileName -- FileName has a size greater than 0.
-t FileDescriptor -- FileDescriptor is open and associated with a terminal.
-u FileName -- FileName's Set User ID bit is set.

-w FileName -- FileName's write flag is on. However, the FileName will
not be writable on a read-only file system even if test indicates true.

-x FileName -- FileName's execute flag is on.
If the specified file exists and is a directory, the True exit value indicates
that the current process has permission to search in the directory.

[edit] String functions

-n String1 -- the length of the String1 variable is nonzero.
-z String1 -- the length of the String1 variable is 0 (zero).
String1 = String2 -- String1 and String2 variables are identical.
String1 != String2 -- String1 and String2 variables are not identical.
String1 -- String1 variable is not a null string.

[edit] Number functions

Integer1 -eq Integer2 -- Integer1 and Integer2 variables are algebraically
equal. Any of the following comparisons can be used in place of -eq.
-ne (not equal)
-gt (greater than)
-ge (greater or equal)
-lt (less than)
-le (less or equal)

file1 -nt file2 -- file1 is newer than file2.
file1 -ot file2 -- file1 is older than file2.
file1 -ef file2 -- file1 is another name for file2. (symbolic link)

[edit] Operators

These functions can be combined with the following operators:

! -- Unary negation operator
-a -- Binary AND operator
-o -- Binary OR operator (the -a operator has higher precedence 
      than the -o operator)
\(Expression\) -- Parentheses for grouping must be escaped with a backslash (\).

The -a and -o operators, along with parentheses for grouping, are XSI extensions^[1] and are therefore not portable. In portable shell scripts, the same effect may be achieved by connecting multiple invocations of test together with the && and || operators and parentheses.

[edit] Exit Status

This command returns the following exit values:

0 The Expression parameter is true.

1 The Expression parameter is false or missing.

>1 An error occurred.

[edit] Examples

1. To test whether a file exists and is not empty, type:

if test ! -s "$1"
then
  echo $1 does not exist or is empty.
fi

If the file specified by the first positional parameter to the shell procedure, $1, does not exist, the test command displays an error message. If $1 exists and has a size greater than 0, the test command displays nothing.

Note: There must be a space between the -s function and the file name.

The quotation marks around $1 ensure that the test works properly even if the value of $1 is a null string. If the quotation marks are omitted and $1 is the empty string, the test command displays the error message

test: argument expected.

2. To do a complex comparison, type:

if [ $# -lt 2 -o ! -e "$1" ]
then
  exit
fi

If the shell procedure is given fewer than two positional parameters or the file specified by $1 does not exist, then the shell procedure exits. The special shell variable $# represents the number of positional parameters entered on the command line that starts this shell procedure.