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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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>
       character:


           eval " $commands"

       or:


           eval " $(some_command)"

EXAMPLES
       foo=10 x=foo
       y='$'$x
       echo $y
       $foo
       eval y='$'$x
       echo $y
       1100

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 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications 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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                              EVAL(1)
