PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       exec — execute commands and open, close, or copy file descriptors

SYNOPSIS         top

       exec [command [argument...]]

DESCRIPTION         top

       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         top

       None.

OPERANDS         top

       See the DESCRIPTION.

STDIN         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       None.

ASYNCHRONOUS EVENTS         top

       Default.

STDOUT         top

       Not used.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       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         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       None.

EXAMPLES         top

       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         top

       Most historical implementations were not conformant in that:

           foo=bar exec cmd

       did not pass foo to cmd.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 2.14, Special Built-In Utilities

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                            EXEC(1P)