PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (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 Section 2.8.1, 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

       Section 2.14, Special Built-In Utilities

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                          EXEC(1POSIX)