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EXEC(1P)                   POSIX Programmer's Manual                  EXEC(1P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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(1P)