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Linux 2.6 - man page for test (linux section 1posix)

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

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  guide-
       line 10 in the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syn-
       tax 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  exe-
	      cute  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  prece-
	      dence 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  pri-
       mary_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, Inter-
	      nationalization 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  interna-
	      tionalization 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  argu-
	      ments).

       LC_MESSAGES
	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic 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 pro-
       duce 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  pri-
       mary.  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 con-
       sidered 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  individ-
       ual  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  vol-
       ume  of IEEE Std 1003.1-2001 because its use is consistent with the -b, -c, -d, and -p op-
       erands ( 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 imple-
       mentations 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 pro-
       posal 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					  TEST(P)


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