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 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
Special Built-In Utilities
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 http://www.opengroup.org/unix/online.html .