./_Man_Solaris_2.5_html/html1/test.1.html

Manual page for if(1)

if, test - evaluate condition(s) or make execution of actions dependent upon the evaluation of condition(s)

SYNOPSIS

/usr/bin/test [condition]

[ condition ]

sh

if condition ; then action ; fi

if condition ; then action ; else action2 ; fi

if condition ; then action ; elif condition2 ; then action2 ; ... ; fi

if condition ; then action ; elif condition2 ; then action2 ; ... ; else action3 ; fi

test condition

[ condition ]

csh

if (condition) then
action
else if (condition2) then
action2
else
action3
endif

if (condition) action

ksh

if condition ; then action ; fi

if condition ; then action ; else action2 ; fi

if condition ; then action ; elif condition2 ; then action2 ; ... ; fi

if condition ; then action ; elif condition2 ; then action2 ; ... ; else action3 ; fi

test condition

[ condition ]

DESCRIPTION

/usr/bin/test

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 second form of the utility, which uses [] rather than test, the square brackets must be separate arguments and condition is optional.

sh

The condition following if is executed and, if it returns a 0 exit status, the action following the first then is executed. Otherwise, the condition2 following elif is executed and, if its value is 0, the action2 following the next then is executed. Failing the if and elif conditions, the else action3 is executed. If no else action or then action is executed, the if command returns a 0 exit status. Any number of elif ... then ... branching pairs are allowed, but only one else.

test evaluates the condition condition and, if its value is true, sets exit status to 0; otherwise, a non-zero (false) exit status is set; test also sets 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 second SYNOPSIS line) must be separate arguments to the test command; normally these items are separated by spaces.

Primitives:

The following primitives are used to construct condition:

-r filename: True if filename exists and is readable.
-w filename: True if filename exists and is writable.
-x filename: True if filename exists and is executable.
-f filename: True if filename 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 filename exists and is (not-a-directory). This is also the default for /usr/bin/csh users.
-d filename: True if filename exists and is a directory.
-h filename: True if filename exists and is a symbolic link. With all other primitives (except -L filename), the symbolic links are followed by default.
-c filename: True if filename exists and is a character special file.
-b filename: True if filename exists and is a block special file.
-p filename: True if filename exists and is a named pipe (fifo).
-u filename: True if filename exists and its set-user-ID bit is set.
-g filename: True if filename exists and its set-group-ID bit is set.
-k filename: True if filename exists and its sticky bit is set.
-s filename: True if filename exists and has a size greater than zero.
-t [ fildes ]: True if the open file whose file descriptor number is fildes (1 by default) is associated with a terminal device.
-z s1: True if the length of string s1 is zero.
-n s1: True if the length of the string s1 is non-zero.
s1 = s2: True if strings s1 and s2 are identical.
s1 != s2: True if strings s1 and s2 are not identical.
s1: True if s1 is not the null string.
n1 -eq n2: True if the integers n1 and n2 are algebraically equal. Any of the comparisons -ne, -gt, -ge, -lt, and -le may be used in place of -eq.
-L filename: True if filename exists and is a symbolic link. With all other primitives (except -h filename), the symbolic links are followed by default.

Operators:

These primaries may be combined with the following operators:

!: Unary negation operator.
-a: Binary and operator.
-o: Binary or operator (-a has higher precedence than -o).
(condition): Parentheses for grouping. Notice also that parentheses are meaningful to the shell and, therefore, must be quoted.

The not-a-directory alternative to the -f option is a transition aid for BSD applications and may not be supported in future releases.

The -L option is a migration aid for users of other shells which have similar options and may not be supported in future releases.

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 correct exit status will be set if you are super-user.

The = and != operators have a higher precedence than the -r through -n operators, and = and != always expect arguments; therefore, = and != cannot be used with the -r through -n operators.

If more than one argument follows the -r through -n operators, only the first argument is examined; the others are ignored, unless a -a or a -o is the second argument.

csh

With the multi-line form of if:

: if condition is true, the action up to the first else or then is executed. Otherwise, if else if condition2 is true, the action2 between the else if and the following else or then is executed. Otherwise, the action3 between the else and the endif is executed.
The if must appear alone on its input line or after an else. Only one endif is needed, but it is required. The words else and endif must be the first nonwhite characters on a line. Any number of else if ... then ... branching pairs are allowed, but only one else.

With the one-line form of if, there are no else, then, or endif keywords:

: if the specified condition evaluates to true, the single action with arguments is executed. Variable substitution on action happens early, at the same time it does for the rest of the if command. action must be a simple command, not a pipeline, a command list, or a parenthesized command list. Note that I/O redirection occurs even if condition is false, when action is not executed (this is a bug).

ksh

The condition following if is executed and, if it returns an exit status of 0, the action following the first then is executed. Otherwise, the condition2 following elif is executed and, if its value is 0, the action2 following the next then is executed. Failing that, the else action3 is executed. If no else action or then action is executed, then the if command returns an exit status of 0. Any number of elif ... then ... branching pairs are allowed, but only one else.

For a description of the test built-in, see the ksh.1 sections "Conditional Expressions" and "Arithmetic Evaluation" as well as the (sh) Bourne shell's test built-in above.

[ condition ] evaluates file attributes, string comparisons, and compound "and" or "or" conditions.

OPERANDS

All operators and elements of primaries must be presented as separate arguments to the test utility.

The following primaries can be used to construct condition:

-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.
-n string: True if the length of string is non-zero.
-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.
-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 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.
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.

These primaries can be combined with the following operator:

! condition: True if condition is false.

The primaries with two elements of the form:

: 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-dependent operators and primary_operator s may be provided by implementations. They will 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 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.

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.

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 condition 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 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 >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"

EXAMPLES

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 3 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

1. Perform a mkdir if a directory does not exist:

: test ! -d tempdir && mkdir tempdir

2. Wait for a file to become non-readable:

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

3. 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

The two forms of the test built-in follow the Bourne shell's if example.

sh

        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

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

csh

        @ 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

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

The Korn shell will also accept the syntax of both the if command and the test command of the Bourne shell.

When using the brackets ([]) within if commands, you must separate both inside ends of the brackets from the inside characters with a space.

ENVIRONMENT

See environ.5 for descriptions of the following environment variables that affect the execution of test: LC_CTYPE, LC_MESSAGES, and NLSPATH.

EXIT STATUS

The following exit values are returned:

0: condition evaluated to true.
1: condition evaluated to false or condition was missing.
>1: An error occurred.

NOTES

Both the Bourne shell, sh, and the Korn shell, ksh, can use the semicolon and the carriage return interchangeably in their syntax of the if, for, and while built-in commands.

Last modified 21/April/97

if, test - evaluate condition(s) or make execution of actions dependent upon the evaluation of condition(s)

SYNOPSIS

sh

csh

ksh

DESCRIPTION

/usr/bin/test

sh

csh

ksh

OPERANDS

USAGE

EXAMPLES

/usr/bin/test

sh

csh

ksh

ENVIRONMENT

EXIT STATUS

SEE ALSO

NOTES