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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 redi-
       rections 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  creat-
       ing a new process.  If arguments are specified, they shall be arguments to command.  Redi-
       rection 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					  EXEC(P)
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