TEST(1P)						     POSIX Programmer's Manual							  TEST(1P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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  indi-
       cates 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  argu-
       ments 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  pri-
       mary.

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 portabil-
       ity 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 argu-
       ment 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 syn-
       tax 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 pro-
       posal. 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 logi-
       cals, 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 con-
       sistent 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 por-
       table 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 implemen-
       tations 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  imple-
       mentations 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 Technol-
       ogy -- 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(1P)