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 differ (con-
       sult 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, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                      EXEC(1P)