NAME
test
, [
—
condition evaluation utility
SYNOPSIS
test |
expression |
[ |
expression ] |
DESCRIPTION
Thetest
utility evaluates
expression and, if it evaluates to true, returns a zero
(true) exit status; otherwise it returns 1 (false). If
expression is not given, test
also returns 1 (false).
All operators and flags are separate arguments to the
test
utility.
The following primaries are used to construct expression:
-b
file- True if file exists and is a block special file.
-c
file- True if file exists and is a character special file.
-d
file- True if file exists and is a directory.
-e
file- True if file exists (regardless of type).
-f
file- True if file exists and is a regular file.
-g
file- True if file exists and its set group ID flag is set.
-h
file- True if file exists and is a symbolic link.
-k
file- True if file exists and its sticky bit is set.
-n
string- True if the length of string is nonzero.
-p
file- True if file exists and is a named pipe (FIFO).
-r
file- True if file exists and is readable.
-s
file- True if file exists and has a size greater than zero.
-t
file_descriptor- True if the file whose file descriptor number is file_descriptor is open and is associated with a terminal.
-u
file- True if file exists and its set user ID flag is set.
-w
file- True if file exists and is writable. True indicates only that the write flag is on. The file is not writable on a read-only file system even if this test indicates true.
-x
file- True if file exists and is executable. True indicates only that the execute flag is on. If file is a directory, true indicates that file can be searched.
-z
string- True if the length of string is zero.
-L
file- True if file exists and is a symbolic link. This
operator is retained for compatibility with previous versions of this
program. Do not rely on its existence; use
-h
instead. -O
file- True if file exists and its owner matches the effective user id of this process.
-G
file- True if file exists and its group matches the effective group id of this process.
-S
file- True if file exists and is a socket.
- file1
-nt
file2 - True if file1 exists and is newer than file2.
- file1
-ot
file2 - True if file1 exists and is older than file2.
- file1
-ef
file2 - True if file1 and file2 exist and refer to the same file.
- string
- True if string is not the null string.
- s1
=
s2 - True if the strings s1 and s2 are identical.
- s1
!=
s2 - True if the strings s1 and s2 are not identical.
- s1
<
s2 - True if string s1 comes before s2 based on the ASCII value of their characters.
- s1
>
s2 - True if string s1 comes after s2 based on the ASCII value of their characters.
- n1
-eq
n2 - True if the integers n1 and n2 are algebraically equal.
- n1
-ne
n2 - True if the integers n1 and n2 are not algebraically equal.
- n1
-gt
n2 - True if the integer n1 is algebraically greater than the integer n2.
- n1
-ge
n2 - True if the integer n1 is algebraically greater than or equal to the integer n2.
- n1
-lt
n2 - True if the integer n1 is algebraically less than the integer n2.
- n1
-le
n2 - True if the integer n1 is algebraically less than or equal to the integer n2.
These primaries can be combined with the following operators:
!
expression- True if expression is false.
- expression1
-a
expression2 - True if both expression1 and expression2 are true.
- expression1
-o
expression2 - True if either expression1 or expression2 is true.
(
expression)
- True if expression is true.
The -a
operator has higher precedence than
the -o
operator.
Note that all file tests with the exception of
-h
and -L
follow symbolic
links and thus evaluate the test for the file pointed at.
EXIT STATUS
The test
utility exits with one of the
following values:
- 0
- expression evaluated to true.
- 1
- expression evaluated to false or was missing.
- >1
- An error occurred.
STANDARDS
The test
utility implements a superset of
the IEEE Std 1003.2 (“POSIX.2”)
specification.
HISTORY
A test
utility appeared in
Version 7 AT&T UNIX.
CAVEATS
The test
grammar is inherently ambiguous.
In order to assure a degree of consistency, the cases described in
IEEE Std 1003.2 (“POSIX.2”) section
4.62.4, are evaluated consistently according to the rules specified in the
standards document. All other cases are subject to the ambiguity in the
command semantics.
This means that test
should not be used
with more than 4 operands (where the terminating ]
in the case of the [
command does not count as an
operand,) and that the obsolete -a
and
-o
options should not be used. Instead invoke
test
multiple times connected by the
“&&” and “||” operators from
sh(1).
When those operators are not used, there is no need for the parentheses as
grouping symbols, so those should also be avoided. Using
sh(1)'s
!
command instead of the equivalent operator from
test
can also protect the script from future test
enhancements.
Most expressions with 3 or less operands will evaluate as
expected, though be aware that with 3 operands, if the second is a known
binary operator, that is always evaluated, regardless of what the other
operands might suggest had been intended. If, and only if, the middle
operand is not a defined binary operator is the first operand examined to
see if it is !
in which case the remaining operands
are evaluated as a two operand test, and the result inverted. The only other
defined three operand case is the meaningless degenerate case where
parentheses (1st and 3rd operands) surround a one operand expression.
With 4 operands there are just two defined cases, the first where
the first operand is !
in which case the result of
the three operand test on the remaining operands is inverted, and the second
is similar to the 3 operand case, the degenerate case of parentheses
surrounding an (in this case) 2 operand test expression.