On Sun, Sep 27, 2020 at 03:19:17PM -0700, Will McGinnis via rsync
<rsync@lists.samba.org> wrote:
> Hello, A GUI program uses rsync for network transfers. It is able to
> load filters from a file by putting a dot and underscore before it.
> Example:mkdir 1 2; touch 1/a .empty; rsync -f ._empty 1/ 2/
>
> Is the dot underscore specific to rsync or is it a general bash (or
> similar?) feature to load arguments from a file? And is it documented
> anywhere for rsync?
>From the manpage:
FILTER RULES
[...]
Rsync builds an ordered list of filter rules as
specified on the command-line. Filter rules have
the following syntax:
RULE [PATTERN_OR_FILENAME]
RULE,MODIFIERS [PATTERN_OR_FILENAME]
You have your choice of using either short or long
RULE names, as described below. If you use a
short-named rule, the ',' separating the RULE
from the MODIFIERS is optional. The PATTERN or
FILE- NAME that follows (when present) must come
after either a single space or an underscore (_).
Here are the available rule prefixes:
merge, '.'
specifies a merge-file to read for more rules.
So the "." means load rules from a file, and the "_"
is like an alternative to a space for separating the
"." and the filename. It seems that the space isn't
optional when using the short form, like the comma is.
I think this is rsync-specific.
I have seen programs use a convention of an "@" prefix
to an option argument to indicate that the rest of the
option argument is a filename to read the real option
arguments from. And I have seen libraries that provide
command line option functionality with support for
config files for default options.
A general purpose way of getting command line options
from a file, if you have a shell available, is to store
command line options in a file like this:
--optiona ...
--optionb ...
--optionc ...
And then use them with on the command line like this:
cmd `cat cmd-options` args...
cheers,
raf
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