exec(1p) - phpMan

EXEC(P)                                                                EXEC(P)



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 sta-
       tus 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 .



POSIX                                2003                              EXEC(P)

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