test(1posix)
NAME
test --- evaluate expression
SYNOPSIS
test [expression] [ [expression] ]
DESCRIPTION
The test utility shall evaluate the expression and indicate the result of the evaluation by its exit status. An exit status of zero indicates that the expression evaluated as true and an exit status of 1 indicates that the expression evaluated as false. In the second form of the utility, which uses "[]" rather than test, the application shall ensure that the square brackets are separate arguments.
OPTIONS
The test utility shall not recognize the "" argument in the manner specified by Guideline 10 in the Base Definitions volume of POSIX.12008, Section 12.2, Utility Syntax Guidelines. No options shall be supported.
OPERANDS
The application shall ensure that all operators and elements of
primaries are presented as separate arguments to the test utility.
The following primaries can be used to construct expression:
b pathname
True if pathname resolves to en existing directory entry for
a block special file. False if pathname cannot be resolved,
or if pathname resolves to an existing directory entry for a
file that is not a block special file.
c pathname
True if pathname resolves to an existing directory entry for
a character special file. False if pathname cannot be
resolved, or if pathname resolves to an existing directory
entry for a file that is not a character special file.
d pathname
True if pathname resolves to an existing directory entry for
a directory. False if pathname cannot be resolved, or if
pathname resolves to an existing directory entry for a file
that is not a directory.
e pathname
True if pathname resolves to an existing directory entry.
False if pathname cannot be resolved.
f pathname
True if pathname resolves to an existing directory entry for
a regular file. False if pathname cannot be resolved, or if
pathname resolves to an existing directory entry for a file
that is not a regular file.
g pathname
True if pathname resolves to an existing directory entry for
a file that has its set-group-ID flag set. False if pathname
cannot be resolved, or if pathname resolves to an existing
directory entry for a file that does not have its set-group-
ID flag set.
h pathname
True if pathname resolves to an existing directory entry for
a symbolic link. False if pathname cannot be resolved, or if
pathname resolves to an existing directory entry for a file
that is not a symbolic link. If the final component of
pathname is a symbolic link, that symbolic link is not
followed.
L pathname
True if pathname resolves to an existing directory entry for
a symbolic link. False if pathname cannot be resolved, or if
pathname resolves to an existing directory entry for a file
that is not a symbolic link. If the final component of
pathname is a symbolic link, that symbolic link is not
followed.
n string True if the length of string is non-zero; otherwise, false.
p pathname
True if pathname resolves to an existing directory entry for
a FIFO. False if pathname cannot be resolved, or if pathname
resolves to an existing directory entry for a file that is
not a FIFO.
r pathname
True if pathname resolves to an existing directory entry for
a file for which permission to read from the file will be
granted, as defined in Section 1.1.1.4, File Read, Write, and
Creation. False if pathname cannot be resolved, or if
pathname resolves to an existing directory entry for a file
for which permission to read from the file will not be
granted.
S pathname
True if pathname resolves to an existing directory entry for
a socket. False if pathname cannot be resolved, or if
pathname resolves to an existing directory entry for a file
that is not a socket.
s pathname
True if pathname resolves to an existing directory entry for
a file that has a size greater than zero. False if pathname
cannot be resolved, or if pathname resolves to an existing
directory entry for a file that does not have a size greater
than zero.
t file_descriptor
True if file descriptor number file_descriptor is open and is
associated with a terminal. False if file_descriptor is not a
valid file descriptor number, or if file descriptor number
file_descriptor is not open, or if it is open but is not
associated with a terminal.
u pathname
True if pathname resolves to an existing directory entry for
a file that has its set-user-ID flag set. False if pathname
cannot be resolved, or if pathname resolves to an existing
directory entry for a file that does not have its set-user-ID
flag set.
w pathname
True if pathname resolves to an existing directory entry for
a file for which permission to write to the file will be
granted, as defined in Section 1.1.1.4, File Read, Write, and
Creation. False if pathname cannot be resolved, or if
pathname resolves to an existing directory entry for a file
for which permission to write to the file will not be
granted.
x pathname
True if pathname resolves to an existing directory entry for
a file for which permission to execute the file (or search
it, if it is a directory) will be granted, as defined in
Section 1.1.1.4, File Read, Write, and Creation. False if
pathname cannot be resolved, or if pathname resolves to an
existing directory entry for a file for which permission to
execute (or search) the file will not be granted.
z string True if the length of string string is zero; otherwise,
false.
string True if the string string is not the null string; otherwise,
false.
s1 = s2 True if the strings s1 and s2 are identical; otherwise,
false.
s1 != s2 True if the strings s1 and s2 are not identical; otherwise,
false.
n1 eq n2 True if the integers n1 and n2 are algebraically equal;
otherwise, false.
n1 ne n2 True if the integers n1 and n2 are not algebraically equal;
otherwise, false.
n1 gt n2 True if the integer n1 is algebraically greater than the
integer n2; otherwise, false.
n1 ge n2 True if the integer n1 is algebraically greater than or equal
to the integer n2; otherwise, false.
n1 lt n2 True if the integer n1 is algebraically less than the integer
n2; otherwise, false.
n1 le n2 True if the integer n1 is algebraically less than or equal to
the integer n2; otherwise, false.
expression1 a expression2
True if both expression1 and expression2 are true; otherwise,
false. The a binary primary is left associative. It has a
higher precedence than o.
expression1 o expression2
True if either expression1 or expression2 is true; otherwise,
false. The o binary primary is left associative.
With the exception of the h pathname and L pathname primaries, if a
pathname argument is a symbolic link, test shall evaluate the
expression by resolving the symbolic link and using the file referenced
by the link.
These primaries can be combined with the following operators:
! expression
True if expression is false. False if expression is true.
( expression )
True if expression is true. False if expression is false. The
parentheses can be used to alter the normal precedence and
associativity.
The primaries with two elements of the form:
primary_operator primary_operand
are known as unary primaries. The primaries with three elements in
either of the two forms:
primary_operand primary_operator primary_operand
primary_operand primary_operator primary_operand
are known as binary primaries. Additional implementation-defined
operators and primary_operators may be provided by implementations.
They shall be of the form operator where the first character of
operator is not a digit.
The algorithm for determining the precedence of the operators and the
return value that shall be generated is based on the number of
arguments presented to test. (However, when using the "[...]" form,
the <right-square-bracket> final argument shall not be counted in this
algorithm.)
In the following list, $1, $2, $3, and $4 represent the arguments
presented to test:
0 arguments:
Exit false (1).
1 argument: Exit true (0) if $1 is not null; otherwise, exit false.
2 arguments:
* If $1 is '!', exit true if $2 is null, false if $2 is
not null.
* If $1 is a unary primary, exit true if the unary test
is true, false if the unary test is false.
* Otherwise, produce unspecified results.
3 arguments:
* If $2 is a binary primary, perform the binary test of
$1 and $3.
* If $1 is '!', negate the two-argument test of $2 and
$3.
* If $1 is '(' and $3 is ')', perform the unary test of
$2. On systems that do not support the XSI option, the
results are unspecified if $1 is '(' and $3 is ')'.
* Otherwise, produce unspecified results.
4 arguments:
* If $1 is '!', negate the three-argument test of $2, $3,
and $4.
* If $1 is '(' and $4 is ')', perform the two-argument
test of $2 and $3. On systems that do not support the
XSI option, the results are unspecified if $1 is '('
and $4 is ')'.
* Otherwise, the results are unspecified.
>4 arguments:
The results are unspecified.
On XSI-conformant systems, combinations of primaries and
operators shall be evaluated using the precedence and
associativity rules described previously. In addition, the
string comparison binary primaries '=' and "!=" shall have
a higher precedence than any unary primary.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of test:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions
volume of POSIX.12008, Section 8.2, Internationalization
Variables for the precedence of internationalization
variables used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of
all the other internationalization variables.
LC_CTYPE Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments).
LC_MESSAGES
Determine the locale that should be used to affect the format
and contents of diagnostic messages written to standard
error.
NLSPATH Determine the location of message catalogs for the processing
of LC_MESSAGES.
ASYNCHRONOUS EVENTS
Default.
STDOUT
Not used.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 expression evaluated to true.
1 expression evaluated to false or expression was missing.
>1 An error occurred.
CONSEQUENCES OF ERRORS
Default. The following sections are informative.
APPLICATION USAGE
The XSI extensions specifying the a and o binary primaries and the
'(' and ')' operators have been marked obsolescent. (Many expressions
using them are ambiguously defined by the grammar depending on the
specific expressions being evaluated.) Scripts using these expressions
should be converted to the forms given below. Even though many
implementations will continue to support these obsolescent forms,
scripts should be extremely careful when dealing with user-supplied
input that could be confused with these and other primaries and
operators. Unless the application developer knows all the cases that
produce input to the script, invocations like:
test "$1" a "$2"
should be written as:
test "$1" && test "$2"
to avoid problems if a user supplied values such as $1 set to '!' and
$2 set to the null string. That is, in cases where maximal portability
is of concern, replace:
test expr1 a expr2
with:
test expr1 && test expr2
and replace:
test expr1 o expr2
with:
test expr1 || test expr2
but note that, in test, a has higher precedence than o while "&&" and
"||" have equal precedence in the shell.
Parentheses or braces can be used in the shell command language to
effect grouping.
Parentheses must be escaped when using sh; for example:
test \( expr1 a expr2 \) o expr3
This command is not always portable even on XSI-conformant systems
depending on the expressions specified by expr1, expr2, and expr3. The
following form can be used instead:
( test expr1 && test expr2 ) || test expr3
The two commands:
test "$1"
test ! "$1"
could not be used reliably on some historical systems. Unexpected
results would occur if such a string expression were used and $1
expanded to '!', '(', or a known unary primary. Better constructs are:
test n "$1"
test z "$1"
respectively.
Historical systems have also been unreliable given the common
construct:
test "$response" = "expected string"
One of the following is a more reliable form:
test "X$response" = "Xexpected string"
test "expected string" = "$response"
Note that the second form assumes that expected string could not be
confused with any unary primary. If expected string starts with '',
'(', '!', or even '=', the first form should be used instead. Using the
preceding rules without the XSI marked extensions, any of the three
comparison forms is reliable, given any input. (However, note that the
strings are quoted in all cases.)
Because the string comparison binary primaries, '=' and "!=", have a
higher precedence than any unary primary in the greater than 4 argument
case, unexpected results can occur if arguments are not properly
prepared. For example, in:
test d $1 o d $2
If $1 evaluates to a possible directory name of '=', the first three
arguments are considered a string comparison, which shall cause a
syntax error when the second d is encountered. One of the following
forms prevents this; the second is preferred:
test \( d "$1" \) o \( d "$2" \)
test d "$1" || test d "$2"
Also in the greater than 4 argument case:
test "$1" = "bat" a "$2" = "ball"
syntax errors occur if $1 evaluates to '(' or '!'. One of the
following forms prevents this; the third is preferred:
test "X$1" = "Xbat" a "X$2" = "Xball"
test "$1" = "bat" && test "$2" = "ball"
test "X$1" = "Xbat" && test "X$2" = "Xball"
EXAMPLES
1. Exit if there are not two or three arguments (two variations):
if [ $# ne 2 ] && [ $# ne 3 ]; then exit 1; fi
if [ $# lt 2 ] || [ $# gt 3 ]; then exit 1; fi
2. Perform a mkdir if a directory does not exist:
test ! d tempdir && mkdir tempdir
3. Wait for a file to become non-readable:
while test r thefile
do
sleep 30
done
echo '"thefile" is no longer readable'
4. Perform a command if the argument is one of three strings (two
variations):
if [ "$1" = "pear" ] || [ "$1" = "grape" ] || [ "$1" = "apple" ]
then
command
fi
case "$1" in
pear|grape|apple) command ;;
esac
RATIONALE
The KornShell-derived conditional command (double bracket [[]]) was
removed from the shell command language description in an early
proposal. Objections were raised that the real problem is misuse of the
test command ([), and putting it into the shell is the wrong way to fix
the problem. Instead, proper documentation and a new shell reserved
word (!) are sufficient.
Tests that require multiple test operations can be done at the shell
level using individual invocations of the test command and shell
logicals, rather than using the error-prone o flag of test.
XSI-conformant systems support more than four arguments.
XSI-conformant systems support the combining of primaries with the
following constructs:
expression1 a expression2
True if both expression1 and expression2 are true.
expression1 o expression2
True if at least one of expression1 and expression2 are true.
( expression )
True if expression is true.
In evaluating these more complex combined expressions, the following
precedence rules are used:
* The unary primaries have higher precedence than the algebraic
binary primaries.
* The unary primaries have lower precedence than the string binary
primaries.
* The unary and binary primaries have higher precedence than the
unary string primary.
* The ! operator has higher precedence than the a operator, and the
a operator has higher precedence than the o operator.
* The a and o operators are left associative.
* The parentheses can be used to alter the normal precedence and
associativity.
The BSD and System V versions of f are not the same. The BSD
definition was:
f file True if file exists and is not a directory.
The SVID version (true if the file exists and is a regular file) was
chosen for this volume of POSIX.12008 because its use is consistent
with the b, c, d, and p operands (file exists and is a specific
file type).
The e primary, possessing similar functionality to that provided by
the C shell, was added because it provides the only way for a shell
script to find out if a file exists without trying to open the file.
Since implementations are allowed to add additional file types, a
portable script cannot use:
test b foo o c foo o d foo o f foo o p foo
to find out if foo is an existing file. On historical BSD systems, the
existence of a file could be determined by:
test f foo o d foo
but there was no easy way to determine that an existing file was a
regular file. An early proposal used the KornShell a primary (with the
same meaning), but this was changed to e because there were concerns
about the high probability of humans confusing the a primary with the
a binary operator.
The following options were not included in this volume of POSIX.12008,
although they are provided by some implementations. These operands
should not be used by new implementations for other purposes:
k file True if file exists and its sticky bit is set.
C file True if file is a contiguous file.
V file True if file is a version file.
The following option was not included because it was undocumented in
most implementations, has been removed from some implementations
(including System V), and the functionality is provided by the shell
(see Section 2.6.2, Parameter Expansion.
l string The length of the string string.
The b, c, g, p, u, and x operands are derived from the SVID;
historical BSD does not provide them. The k operand is derived from
System V; historical BSD does not provide it.
On historical BSD systems, test w directory always returned false
because test tried to open the directory for writing, which always
fails.
Some additional primaries newly invented or from the KornShell appeared
in an early proposal as part of the conditional command ([[]]): s1 >
s2, s1 < s2, str = pattern, str != pattern, f1 nt f2, f1 ot f2, and
f1 ef f2. They were not carried forward into the test utility when
the conditional command was removed from the shell because they have
not been included in the test utility built into historical
implementations of the sh utility.
The t file_descriptor primary is shown with a mandatory argument
because the grammar is ambiguous if it can be omitted. Historical
implementations have allowed it to be omitted, providing a default of
1.
It is noted that '[' is not part of the portable filename character
set; however, since it is required to be encoded by a single byte, and
is part of the portable character set, the name of this utility forms a
character string across all supported locales.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 1.1.1.4, File Read, Write, and Creation, find The Base Definitions volume of POSIX.12008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html . Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
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