bionic (1) exec.1posix.gz

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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


       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 .