posix man page for eval

EVAL(1P)						     POSIX Programmer's Manual							  EVAL(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
       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 delimiter, 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>  charac-
       ter:

	   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
       options supported as an extension (or errors reported for unsupported options), 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, 2013 Edition, Standard for Information Technol-
       ogy -- 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 Stan-
       dard 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 .

IEEE
/The Open Group						       2013								  EVAL(1P)