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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 IEEE Std 1003.1-2001, 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 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.
-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.
-L file
True if file exists and is a symbolic link.
-n string
True if the length of string is non-zero.
-p file
True if file is a FIFO.
-r file
True if file exists and is readable. True shall indicate that permission to read from file will be
granted, as defined in File Read, Write, and Creation .
-S file
True if file exists and is a socket.
-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 shall indicate that permission to write from file will
be granted, as defined in File Read, Write, and Creation .
-x file
True if file exists and is executable. True shall indicate that permission to execute file will be
granted, as defined in File Read, Write, and Creation . If file is a directory, true shall
indicate that permission to search file will be granted.
-z string
True if the length of string string is zero.
string True if the string 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.
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.
expression1 -a expression2
True if both expression1 and expression2 are true. 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. The -o binary primary is left associative.
With the exception of the -h file and -L file primaries, if a file 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.
( expression )
True if expression is true. 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-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.
* 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.
* 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 IEEE Std 1003.1-2001, 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
Scripts should be careful when dealing with user-supplied input that could be confused with primaries and
operators. Unless the application writer 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 outside XSI-conformant systems. 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 -a $# -ne 3 ]; then exit 1; fi
if [ $# -lt 2 -o $# -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
IEEE Std 1003.1-2001 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 IEEE Std 1003.1-2001, 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 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.
FUTURE DIRECTIONS
None.
SEE ALSO
File Read, Write, and Creation , find
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. 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.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 TEST(P)