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 .