Originální popis anglicky:
exec - execute commands and open, close, or copy file descriptors
Návod, kniha: POSIX Programmer's Manual
exec [command [argument ...]]
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.
None.
See the DESCRIPTION.
Not used.
None.
None.
Default.
Not used.
The standard error shall be used only for diagnostic messages.
None.
None.
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.
Default.
The following sections are informative.
None.
Open
readfile as file descriptor 3 for reading:
Open
writefile as file descriptor 4 for writing:
Make file descriptor 5 a copy of file descriptor 0:
Close file descriptor 3:
Cat the file
maggie by replacing the current shell with the
cat
utility:
Most historical implementations were not conformant in that:
did not pass
foo to
cmd.
None.
Special Built-In Utilities
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
.
