EVAL(1POSIX)               POSIX Programmer's Manual              EVAL(1POSIX)

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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
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NAME
       eval -- construct command by concatenating arguments

SYNOPSIS
       eval [argument...]

DESCRIPTION
       The eval utility shall construct a command by  concatenating  arguments
       together,  separating  each  with a <space> character.  The constructed
       command shall be read and executed by the shell.

OPTIONS
       None.

OPERANDS
       See the DESCRIPTION.

STDIN
       Not used.

INPUT FILES
       None.

ENVIRONMENT VARIABLES
       None.

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
       If there are no arguments, or only null arguments, eval shall return  a
       zero  exit  status;  otherwise,  it shall return the exit status of the
       command defined by the string of concatenated  arguments  separated  by
       <space>  characters,  or  a  non-zero  exit status if the concatenation
       could not be parsed as a command and  the  shell  is  interactive  (and
       therefore did not abort).

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       Since  eval is not required to recognize the "--" end of options delim-
       iter, in cases where the argument(s) to eval might begin with '-' it is
       recommended  that  the first argument is prefixed by a string that will
       not alter the commands to be executed, such as a <space> character:

           eval " $commands"

       or:

           eval " $(some_command)"

EXAMPLES
       foo=10 x=foo
       y='$'$x
       echo $y
       $foo
       eval y='$'$x
       echo $y
       10

RATIONALE
       This standard allows, but does not require,  eval  to  recognize  "--".
       Although this means applications cannot use "--" to protect against op-
       tions supported as an extension (or errors reported for unsupported op-
       tions),  the nature of the eval utility is such that other means can be
       used to provide this protection (see APPLICATION USAGE above).

FUTURE DIRECTIONS
       None.

SEE ALSO
       Section 2.14, Special Built-In Utilities

COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por-
       table Operating System Interface (POSIX), The Open Group Base  Specifi-
       cations  Issue  7, 2018 Edition, Copyright (C) 2018 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 .

       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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                  2017                         EVAL(1POSIX)

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