eval(1p) — Linux manual page

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 1003.1-2017, 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(1P)

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