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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 (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  re-
       direction  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 com-
       mand  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  util-
       ity:
           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, 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 Electri-
       cal  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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                             EXEC(1P)