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       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding 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 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  Guideline  10  in  the
       Base Definitions volume of POSIX.1‐2008, 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 pathname
                 True if pathname resolves to en existing directory entry for a block special  file.   False  if
                 pathname  cannot be resolved, or if pathname resolves to an existing directory entry for a file
                 that is not a block special file.

       −c pathname
                 True if pathname resolves to an existing directory entry for a character special  file.   False
                 if  pathname  cannot  be resolved, or if pathname resolves to an existing directory entry for a
                 file that is not a character special file.

       −d pathname
                 True if pathname resolves to an existing directory entry for a  directory.  False  if  pathname
                 cannot  be  resolved, or if pathname resolves to an existing directory entry for a file that is
                 not a directory.

       −e pathname
                 True if pathname resolves to an existing directory entry. False if pathname cannot be resolved.

       −f pathname
                 True if pathname resolves to an existing directory entry for a regular file. False if  pathname
                 cannot  be  resolved, or if pathname resolves to an existing directory entry for a file that is
                 not a regular file.

       −g pathname
                 True if pathname resolves to an existing directory entry for a file that has  its  set-group-ID
                 flag  set.  False  if  pathname  cannot  be  resolved,  or  if pathname resolves to an existing
                 directory entry for a file that does not have its set-group-ID flag set.

       −h pathname
                 True if pathname resolves to an existing directory entry for a symbolic link. False if pathname
                 cannot  be  resolved, or if pathname resolves to an existing directory entry for a file that is
                 not a symbolic link. If the final component of pathname is a symbolic link, that symbolic  link
                 is not followed.

       −L pathname
                 True if pathname resolves to an existing directory entry for a symbolic link. False if pathname
                 cannot be resolved, or if pathname resolves to an existing directory entry for a file  that  is
                 not  a symbolic link. If the final component of pathname is a symbolic link, that symbolic link
                 is not followed.

       −n string True if the length of string is non-zero; otherwise, false.

       −p pathname
                 True if pathname resolves to an existing directory entry for a FIFO. False if  pathname  cannot
                 be  resolved,  or  if pathname resolves to an existing directory entry for a file that is not a
                 FIFO.

       −r pathname
                 True if pathname resolves to an existing directory entry for a file  for  which  permission  to
                 read  from  the  file  will  be  granted,  as defined in Section 1.1.1.4, File Read, Write, and
                 Creation.  False if pathname cannot be  resolved,  or  if  pathname  resolves  to  an  existing
                 directory entry for a file for which permission to read from the file will not be granted.

       −S pathname
                 True if pathname resolves to an existing directory entry for a socket. False if pathname cannot
                 be resolved, or if pathname resolves to an existing directory entry for a file that  is  not  a
                 socket.

       −s pathname
                 True  if  pathname  resolves  to an existing directory entry for a file that has a size greater
                 than zero. False if pathname cannot be  resolved,  or  if  pathname  resolves  to  an  existing
                 directory entry for a file that does not have a size greater than zero.

       −t file_descriptor
                 True if file descriptor number file_descriptor is open and is associated with a terminal. False
                 if file_descriptor is not a  valid  file  descriptor  number,  or  if  file  descriptor  number
                 file_descriptor is not open, or if it is open but is not associated with a terminal.

       −u pathname
                 True  if  pathname  resolves to an existing directory entry for a file that has its set-user-ID
                 flag set. False if pathname cannot  be  resolved,  or  if  pathname  resolves  to  an  existing
                 directory entry for a file that does not have its set-user-ID flag set.

       −w pathname
                 True  if  pathname  resolves  to an existing directory entry for a file for which permission to
                 write to the file will be granted, as  defined  in  Section  1.1.1.4,  File  Read,  Write,  and
                 Creation.   False  if  pathname  cannot  be  resolved,  or  if pathname resolves to an existing
                 directory entry for a file for which permission to write to the file will not be granted.

       −x pathname
                 True if pathname resolves to an existing directory entry for a file  for  which  permission  to
                 execute  the  file  (or search it, if it is a directory) will be granted, as defined in Section
                 1.1.1.4, File Read, Write, and Creation.  False if pathname cannot be resolved, or if  pathname
                 resolves  to an existing directory entry for a file for which permission to execute (or search)
                 the file will not be granted.

       −z string True if the length of string string is zero; otherwise, false.

       string    True if the string string is not the null string; otherwise, false.

       s1 = s2   True if the strings s1 and s2 are identical; otherwise, false.

       s1 != s2  True if the strings s1 and s2 are not identical; otherwise, false.

       n1 −eq n2 True if the integers n1 and n2 are algebraically equal; otherwise, false.

       n1 −ne n2 True if the integers n1 and n2 are not algebraically equal; otherwise, false.

       n1 −gt n2 True if the integer n1 is algebraically greater than the integer n2; otherwise, false.

       n1 −ge n2 True if the integer n1 is algebraically greater than or equal to  the  integer  n2;  otherwise,
                 false.

       n1 −lt n2 True if the integer n1 is algebraically less than the integer n2; otherwise, false.

       n1 −le n2 True if the integer n1 is algebraically less than or equal to the integer n2; otherwise, false.

       expression1 −a expression2
                 True  if  both expression1 and expression2 are true; otherwise, false. 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; otherwise, false. The −o binary  primary  is
                 left associative.

       With  the  exception  of  the −h pathname and −L pathname primaries, if a pathname 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. False if expression is true.

       ( expression )
                 True  if expression is true. False if expression is false. 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_operandprimary_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 arguments presented to test.  (However, when using the "[...]" form,
       the <right-square-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.  On systems that do not support
                       the XSI option, the results are unspecified if $1 is '(' and $3 is ')'.

                    *  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.  On systems  that
                       do not support the XSI option, the results are unspecified if $1 is '(' and $4 is ')'.

                    *  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 POSIX.1‐2008, 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

       The XSI extensions specifying the −a and −o binary primaries and the '('  and  ')'  operators  have  been
       marked  obsolescent. (Many expressions using them are ambiguously defined by the grammar depending on the
       specific expressions being evaluated.) Scripts using these expressions should be converted to  the  forms
       given  below.  Even though many implementations will continue to support these obsolescent forms, scripts
       should be extremely careful when dealing with user-supplied input that could be confused with  these  and
       other primaries and operators. Unless the application developer 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 even on XSI-conformant systems depending on the expressions specified
       by expr1, expr2, and expr3.  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 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 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 ] && [ $# −ne 3 ]; then exit 1; fi
               if [ $# −lt 2 ] || [ $# −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 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 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
       POSIX.1‐2008 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 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 POSIX.1‐2008, 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 Section 2.6.2, 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.

       It is noted that '[' is not part of the portable filename character set; however, since it is required to
       be  encoded by a single byte, and is part of the portable character set, the name of this utility forms a
       character string across all supported locales.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section 1.1.1.4, File Read, Write, and Creation, find

       The Base Definitions volume of POSIX.1‐2008, Chapter 8,  Environment  Variables,  Section  12.2,  Utility
       Syntax Guidelines

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications  Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
       and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .