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EXEC(P)			   POSIX Programmer's Manual		       EXEC(P)

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 re‐
       direction 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 com‐
       mand 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 util‐
       ity:

	      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 .

IEEE/The Open Group		     2003			       EXEC(P)
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