07-18-2007
Help with exec command and file descriptors??
im having trouble with the comprehending the exec command and the use of file descriptors.
given:
#!/bin/sh
exec 4>&1
exec 1>&2
exec 2>&4
exec 4>&-
echo Hello
would the standard output of this script be sent to STDOUT, STDERR or neither and why???
thanks for the help.
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LEARN ABOUT DEBIAN
dh-exec
DH-EXEC(1) dh-exec DH-EXEC(1)
NAME
dh-exec - Debhelper executable file helpers
SYNOPSIS
#! /usr/bin/dh-exec
src/libfoo-*.so.* debian/foo-plugins/usr/lib/foo/${DEB_HOST_MULTIARCH}/
etc/example.conf => debian/foo/etc/foo/foo.conf
DESCRIPTION
dh-exec is a simple program, meant to be used as the interpreter for executable debhelper config files.
It is a wrapper around the various other sub-commands (see below), and will pipe the input file through all of them in turn, using an
ordering that makes most sense in the vast majority of cases.
The order as of now is dh-exec-subst gets run first, followed by dh-exec-install, so that variable expansion happens before files need to
be copied.
ARCHITECTURE
dh-exec is built up from three layers: there is the dh-exec utility, its single entry point, the only thing one will need to call.
Below that, there are the various sub-commands, such as dh-exec-subst, dh-exec-installs and dh-exec-illiterate, which are thin wrappers
around the various dh-exec scripts, that make sure they only run those that need to be run.
And the lowest layer are the various scripts that do the actual work.
One can control which sub-commands to run, or if even more granularity is desired, one can limit which scripts shall be run, too. See below
for the options!
OPTIONS
--with=command[,command ...]
Replace the list of sub-commands to run the input through with a custom list (where entries are separated by whitespace or commas).
This option will always replace the existing list with whatever is specified.
This can be used to explicitly set which sub-commands to use.
The list must not include the dh-exec- prefix.
Defaults to subst,install.
--without=command[,command ...]
Inversely to the option above, this lists all the sub-commands which should not be used.
The list must not include the dh-exec- prefix.
--with-scripts=script[,script ...]
Replace the list of scripts to run the input through with a custom list (where entries are separated by whitespace or commas). This
option will always replace the existing list with whatever is specified.
This can be used to explicitly specify which scripts to use, limiting even beyond what the --with option is capable of.
The list must not include the dh-exec- prefix.
By default it is empty, meaning there is no filtering done, and whatever scripts the sub-commands find, will be run.
--no-act
Do not really do anything, but print the pipeline that would have been run instead.
--list
List the available sub-commands and scripts, grouped by sub-command.
--help, --version
Display a short help or the package version, respectively.
SUB-COMMANDS
dh-exec-subst
Substitutes various variables (either from the environment, or from dpkg-architecture(1)).
dh-exec-install
An extension to dh_install(1), that supports renaming files during the copy process, using a special syntax.
ENVIRONMENT
DH_EXEC_LIBDIR
The directory in which the wrapped sub-commands reside. Defaults to /usr/lib/dh-exec/.
DH_EXEC_SCRIPTDIR
The directory in which the scripts that do the heavy work live. Defaults to /usr/share/dh-exec/.
FILES
$DH_EXEC_LIBDIR/dh-exec-*
The various sub-commands.
$DH_EXEC_SCRIPTDIR/dh-exec-*
The various scripts ran by the sub-commands.
SEE ALSO
debhelper(1), dh-exec-subst(1), dh-exec-install(1)
AUTHOR
dh-exec is copyright (C) 2011-2012 by Gergely Nagy <algernon@madhouse-project.org>.
2012-05-03 DH-EXEC(1)