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 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

       Special Built-In Utilities

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .