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 redi-
       rection 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 Technol-
       ogy -- 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)