Section: POSIX Programmer's Manual (1P)
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.
--- execute commands and open, close, or copy file descriptors
exec [command [argument...]]
utility shall open, close, and/or copy file descriptors as specified by
any redirections as part of the command.
is specified without
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
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.
See the DESCRIPTION.
The standard error shall be used only for diagnostic messages.
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
, Consequences of Shell Errors),
the shell shall exit with a value in the range 1-125. Otherwise,
shall return a zero exit status.
CONSEQUENCES OF ERRORS
The following sections are informative.
as file descriptor 3 for reading:
exec 3< readfile
as file descriptor 4 for writing:
exec 4> writefile
Make file descriptor 5 a copy of file descriptor 0:
Close file descriptor 3:
Cat the file
by replacing the current shell with the
exec cat maggie
Most historical implementations were not conformant in that:
foo=bar exec cmd
did not pass
, Special Built-In Utilities
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
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