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 corresponding
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NAMEeval — construct command by concatenating arguments
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.
See the DESCRIPTION.
The standard error shall be used only for diagnostic messages.
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
The following sections are informative.
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"
eval " $(some_command)"
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).
Section 2.14, Special Built-In Utilities
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 Electri‐
cal 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 .
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IEEE/The Open Group 2013 EVAL(1P)