test(P)                                                 test(P)





NAME
       test - evaluate expression

SYNOPSIS
       test [expression]

       [ [expression] ]


DESCRIPTION
       The test utility shall evaluate the expression and indi-
       cate the result of the evaluation by its exit status. An
       exit status of zero indicates that the expression evalu-
       ated 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 Def-
       initions  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 ele-
       ments  of  primaries are presented as separate arguments
       to the test utility.

       The following primaries can be used to construct expres-
       sion:

       -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 Cre-
              ation  . If file is a directory, true shall indi-
              cate 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  algebrai-
              cally 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 evalu-
       ate  the  expression  by resolving the symbolic link and
       using the file referenced by the link.

       These primaries can be combined with the following oper-
       ators:

       !  expression
              True if expression is false.

       (  expression  )
              True  if  expression is true. The parentheses can
              be used to alter the normal precedence and  asso-
              ciativity.


       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  implementa-
       tion-defined operators and primary_operators may be pro-
       vided 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 internationaliza-
              tion 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  cate-
              gories.)

       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 mes-
              sages 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-sup-
       plied 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-confor-
       mant 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  expres-
       sion 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 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 com-
       parison, which shall cause a syntax error when the  sec-
       ond  -d is encountered.  One of the following forms pre-
       vents 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 pre-
       ferred:


              test "X$1" = "Xbat" -a "X$2" = "Xball"
              test "$1" = "bat" && test "$2" = "ball"
              test "X$1" = "Xbat" && test "X$2" = "Xball"

EXAMPLES
       Exit if there are not two or three arguments (two varia-
       tions):


              if [ $# -ne 2 -a $# -ne 3 ]; then exit 1; fi
              if [ $# -lt 2 -o $# -gt 3 ]; then exit 1; fi

       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):


              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 lan-
       guage description in an early proposal. Objections  were
       raised  that the real problem is misuse of the test com-
       mand ( [), 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 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  pri-
       maries 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  expres-
              sion2 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 prece-
              dence than the unary string primary.

              The  ! operator has higher precedence than the -a
              operator, and the -a operator has  higher  prece-
              dence 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 regu-
       lar   file)   was   chosen   for    this    volume    of
       IEEE Std 1003.1-2001  because its use is consistent 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  implemen-
       tations 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  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  Operat-
       ing System Interface (POSIX), The Open Group Base Speci-
       fications Issue 6, Copyright (C) 2001-2003 by the Insti-
       tute  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.open-
       group.org/unix/online.html .



POSIX                         2003                      test(P)
