exec






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.


exec — execute commands and open, close, or copy file
descriptors



exec [command [argument...]]

The utility shall open, close, and/or copy file descriptors
as specified by any redirections as part of the command.  If
is specified without or 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 is specified
with it shall replace the shell with without creating a new
process. If are specified, they shall be arguments to
Redirection affects the current shell execution environment.

None.

See the DESCRIPTION.

Not used.

None.

None.

Default.

Not used.

The standard error shall be used only for diagnostic
messages.

None.

None.

If is specified, shall not return to the shell; rather, the
exit status of the process shall be the exit status of the
program implementing which overlaid the shell. If is not
found, the exit status shall be 127. If is found, but it is
not an executable utility, the exit status shall be 126. If
a redirection error occurs (see the shell shall exit with a









                             ‐2‐


value in the range 1−125. Otherwise, shall return a zero
exit status.

Default.


None.

Open as file descriptor 3 for reading:

     exec 3< readfile
Open 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 by replacing the current shell with the
utility:

     exec cat maggie

Most historical implementations were not conformant in that:

     foo=bar exec cmd
did not pass to

None.



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 .