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



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

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(1)
