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 ( 2³¹ 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 will be returned even though the file may 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

True, if file exists. (Not available in sh).

-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. Alternatively, if /usr/bin/sh users specify /usr/ucb before /usr/bin in their PATH environment variable, then test will return true if file exists and is (not-a-directory). The csh test and [ built-ins always use this alternative behavior.

-g file

True if file exists and its set group ID flag is set.

-G file

True if file exists and its group matches the effective group ID of this process. (Not available in sh.)

-h file

True if file exists and is a symbolic link.

-k file

True if file exists and has its sticky bit set.

-L file

True, if file exists and is a symbolic link.

-n string

True if the length of string is non-zero.

-o option

True if option named option is on. (Not available in csh or sh.)

-O file

True if file exists and is owned by the effective user ID of this process. (Not available in sh.)

-p file

True if file 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.

-S file

True if file exists and is a socket. (Not available in sh.)

-t [file_descriptor]

True if the file whose file descriptor number is file_descriptor is open and is associated with a terminal. If file_descriptor is not specified, 1 is used as a default value.

-u file

True if file exists and its set-user-ID flag is set.

-w file

True if file exists and is writable. True will indicate only that the write flag is on. The file will not be writable on a read-only file system even if this test indicates true.

-x file

True if file exists and is executable. True will indicate 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 string is zero.

file1-nt file2

True, if file1 exists and is newer than file2. (Not available in sh.)

file1-ot file2

True, if file1 exists and is older than file2. (Not available in sh.)

file1-ef file2

True, if file1 and file2 exist and refer to the same file. (Not available in sh.)

string

True if the string string is not the null string.

string1 = string2

True if the strings string1 and string2 are identical.

string1 != string2

True if the strings string1 and string2 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.

condition1 -a condition2

True if both condition1 and condition2 are true. The -a binary primary is left associative and has higher precedence than the -o binary primary.

condition1 -o condition2

True if either condition1 or condition2 is true. The -o binary primary is left associative.

These primaries can be combined with the following operators:

! condition

True if condition is false.

( condition )

True if condition is true. The parentheses ( ) can be used to alter the normal precedence and associativity. Notice also that parentheses are meaningful to the shell and, therefore, must be quoted.

The algorithm for determining the precedence of the operators and the return value that will be generated is based on the number of arguments presented to test. (However, when using the [...] form, the right-bracket final argument will not be 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:

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.
• Otherwise, produce unspecified results.

4 arguments:

• If $1 is !, negate the three-argument test of $2, $3, and $4.
• Otherwise, the results are unspecified.

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"

Notice 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 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 will 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:

• if a variable set to 1 is greater than 0,
• if a variable set to 2 is equal to 2, and
• if the word "root" is included in the text file /etc/passwd.

/usr/bin/test

test ! -d tempdir && mkdir tempdir

while test -r thefile
do
   sleep 30
done
echo'"thefile" is no longer readable'

if [ "$1" = "pear" ] || [ "$1" = "grape" ] || [ "$1" = "apple" ]
then
    command
fi
case "$1" in
    pear|grape|apple) command;;
esac

The test 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

csh

ksh

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: LC_CTYPE, LC_MESSAGES, and NLSPATH.

The following exit values are returned:

0

condition evaluated to true.

1

condition evaluated to false or condition was missing.

>1

An error occurred.

See attributes(5) for descriptions of the following attributes:

csh(1), ksh(1), sh(1), test(1B), attributes(5), environ(5), largefile(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.