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

PROLOG         top

       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         top

       eval — construct command by concatenating arguments

SYNOPSIS         top

       eval [argument...]

DESCRIPTION         top

       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         top

       None.

OPERANDS         top

       See the DESCRIPTION.

STDIN         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       None.

ASYNCHRONOUS EVENTS         top

       Default.

STDOUT         top

       Not used.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       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         top

       Default.
       The following sections are informative.

APPLICATION USAGE         top

       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         top

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

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       Section 2.14, Special Built-In Utilities

COPYRIGHT         top

       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 .
IEEE/The Open Group                 2013                            EVAL(1P)