EXEC
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
exec
--- execute commands and open, close, or copy file descriptors
SYNOPSIS
exec [command [argument...]]
DESCRIPTION
The
exec
utility shall open, close, and/or copy file descriptors as specified by
any redirections as part of the command.
If
exec
is specified without
command
or
arguments,
and any file descriptors with numbers greater than 2 are opened with
associated redirection statements, it is unspecified whether those file
descriptors remain open when the shell invokes another utility.
Scripts concerned that child shells could misuse open file descriptors
can always close them explicitly, as shown in one of the following
examples.
If
exec
is specified with
command,
it shall replace the shell with
command
without creating a new process. If
arguments
are specified, they shall be arguments to
command.
Redirection affects the current shell execution environment.
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
command
is specified,
exec
shall not return to the shell; rather, the exit status of the process
shall be the exit status of the program implementing
command,
which overlaid the shell. If
command
is not found, the exit status shall be 127. If
command
is found, but it is not an executable utility, the exit status shall be
126. If a redirection error occurs (see
Section 2.8.1,
Consequences of Shell Errors),
the shell shall exit with a value in the range 1-125. Otherwise,
exec
shall return a zero exit status.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
None.
EXAMPLES
Open
readfile
as file descriptor 3 for reading:
-
exec 3< readfile
Open
writefile
as file descriptor 4 for writing:
-
exec 4> writefile
Make file descriptor 5 a copy of file descriptor 0:
-
exec 5<&0
Close file descriptor 3:
-
exec 3<&-
Cat the file
maggie
by replacing the current shell with the
cat
utility:
-
exec cat maggie
RATIONALE
Most historical implementations were not conformant in that:
-
foo=bar exec cmd
did not pass
foo
to
cmd.
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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