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test - evaluate condition(s)
/usr/bin/test [condition]
[ [condition] ]
test [condition]
[ [condition] ]
test [condition]
[ [condition] ]
test [condition]
[ [condition] ]
test [condition]
[ [condition] ]
The test utility evaluates the condition and indicates the result of the evaluation by its exit status. An exit status of zero indicates that the condition evaluated as true and an exit status of 1 indicates that the condition evaluated as false.
In the first form of the utility shown using the SYNOPSIS:
test [condition]
the square brackets denote that condition is an optional operand and are not to be entered on the command line.
In the second form of the utility shown using the SYNOPSIS:
[ [ condition ] ]
the first open square bracket, [, is the required utility name. condition is optional, as denoted by the inner pair of square brackets. The final close square bracket, ], is a required operand.
See largefile(5) for the description of the behavior of test when encountering files greater than or equal to 2 Gbyte (2^31 bytes).
The test and [ utilities evaluate the condition condition and, if its value is true, set exit status to 0. Otherwise, a non-zero (false) exit status is set. test and [ also set a non-zero exit status if there are no arguments. When permissions are tested, the effective user ID of the process is used.
All operators, flags, and brackets (brackets used as shown in the last SYNOPSIS line) must be separate arguments to these commands. Normally these arguments are separated by spaces.
The primaries listed below 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.
If any file operands except for -h and -L primaries refer to symbolic links, the symbolic link is expanded and the test is performed on the resulting file.
If you test a file you own (the -r -w or -x tests), but the permission tested does not have the owner bit set, a non-zero (false) exit status is returned even though the file can have the group or other bit set for that permission.
The = and != primaries have a higher precedence than the unary primaries. The = and != primaries always expect arguments; therefore, = and != cannot be used as an argument to the unary primaries.
The following primaries can be used to construct condition:
-a file
-b file
-c file
-d file
-e file
-f file
-g file
-G file
-h file
-k file
-L file
-n string
-o option
-O file
-p file
-r file
-s file
-S file
-t [file_descriptor]
-u file
-w file
-x file
-z string
file1 -nt file2
file1 -ot file2
file1 -ef file2
string
string1 = string2
string1 != string2
n1 -eq n2
n1 -ne n2
n1 -gt n2
n1 -ge n2
n1 -lt n2
n1 -le n2
condition1 -a condition2
condition1 -o condition2
These primaries can be combined with the following operators:
! condition
( condition )
The algorithm for determining the precedence of the operators and the return value that is generated is based on the number of arguments presented to test. (However, when using the [...] form, the right-bracket final argument is not counted in this algorithm.)
In the following list, $1, $2, $3 and $4 represent the arguments presented to test as a condition, condition1, or condition2.
0 arguments:
1 argument:
2 arguments:
3 arguments:
4 arguments:
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 notice 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 condition were used and $1 expanded to !, (, or a known unary primary. Better constructs are, respectively,
test -n "$1" test -z "$1"
Historical systems have also been unreliable given the common construct:
test "$response" = "expected string"
One of the following is a more reliable form:
test "X$response" = "Xexpected string" test "expected string" = "$response"
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 marked extensions, any of the three comparison forms is reliable, given any input. (However, observe 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 >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 causes a syntax error when the second -d is encountered. 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 >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"
In the if command examples, three conditions are tested, and if all three evaluate as true or successful, then their validities are written to the screen. The three tests are:
Example 1 Using /usr/bin/test
Perform a mkdir if a directory does not exist:
test ! -d tempdir && mkdir tempdir
Wait for a file to become non-readable:
while test -r thefile do sleep 30 done echo'"thefile" is no longer readable'
Perform a command if the argument is one of three strings (two variations), using the open bracket version [ of the test command:
if [ "$1" = "pear" ] || [ "$1" = "grape" ] || [ "$1" = "apple" ] then command fi case "$1" in pear|grape|apple) command;; esac
Example 2 Using /usr/bin/test for the -e option
If one really wants to use the -e option in sh, use /usr/bin/test, as in the following:
if [ ! -h $PKG_INSTALL_ROOT$rLink ] && /usr/bin/test -e $PKG_INSTALL_ROOT/usr/bin/$rFile ; then ln -s $rFile $PKG_INSTALL_ROOT$rLink fi
The two forms of the test built-in follow the Bourne shell's if example.
Example 3 Using the sh built-in
ZERO=0 ONE=1 TWO=2 ROOT=root
if [ $ONE -gt $ZERO ]
[ $TWO -eq 2 ]
grep $ROOT /etc/passwd >&1 > /dev/null # discard output
then
echo "$ONE is greater than 0, $TWO equals 2, and $ROOT is" \
"a user-name in the password file"
else
echo "At least one of the three test conditions is false"
fi
Example 4 Using the test built-in
Examples of the test built-in:
test `grep $ROOT /etc/passwd >&1 /dev/null` # discard output echo $? # test for success [ `grep nosuchname /etc/passwd >&1 /dev/null` ] echo $? # test for failure
Example 5 Using the csh built-in
@ ZERO = 0; @ ONE = 1; @ TWO = 2; set ROOT = root
grep $ROOT /etc/passwd >&1 /dev/null # discard output
# $status must be tested for immediately following grep
if ( "$status" == "0" && $ONE > $ZERO && $TWO == 2 ) then
echo "$ONE is greater than 0, $TWO equals 2, and $ROOT is" \
"a user-name in the password file"
endif
Example 6 Using the ksh built-in
ZERO=0 ONE=1 TWO=$((ONE+ONE)) ROOT=root
if ((ONE > ZERO)) # arithmetical comparison
[[ $TWO = 2 ]] # string comparison
[ `grep $ROOT /etc/passwd >&1 /dev/null` ] # discard output
then
echo "$ONE is greater than 0, $TWO equals 2, and $ROOT is" \
"a user-name in the password file"
else
echo "At least one of the three test conditions is false"
fi
See environ(5) for descriptions of the following environment variables that affect the execution of test: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, and NLSPATH.
The following exit values are returned:
0
1
>1
See attributes(5) for descriptions of the following attributes:
| ||||||||||||
| |||||||||
csh(1), ksh(1), ksh93(1), sh(1), test(1B), attributes(5), environ(5), largefile(5), standards(5)
The not-a-directory alternative to the -f option is a transition aid for BSD applications and may not be supported in future releases.
When comparing file timestamps, the ksh93 test built-in handles high-resolution timestamps of up to nanosecond granularity, for file systems which support them.
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Created 1996-2024 by Maxim Chirkov Добавить, Поддержать, Вебмастеру |