EVAL
Section: POSIX Programmer's Manual (1P)
Updated: 2013
Index
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PROLOG
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
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
dq--dq
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
10
RATIONALE
This standard allows, but does not require,
eval
to recognize
dq--dq.
Although this means applications cannot use
dq--dq
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 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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- OPERANDS
-
- STDIN
-
- INPUT FILES
-
- ENVIRONMENT VARIABLES
-
- ASYNCHRONOUS EVENTS
-
- STDOUT
-
- STDERR
-
- OUTPUT FILES
-
- EXTENDED DESCRIPTION
-
- EXIT STATUS
-
- CONSEQUENCES OF ERRORS
-
- APPLICATION USAGE
-
- EXAMPLES
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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