Jakub Jankowski <shasta@toxcorp.com> writes:
Friday 08 of April 2011 00:51:23 Balazs Scheidler napisał(a):
On Thu, 2011-04-07 at 15:01 +0200, Jakub Jankowski wrote:
I'd like to implement simple hashing in file() destination, mainly to avoid ext3 32k directories limit, but also for convenience. Is it possible to do something simliar what this shell snippet does: $ NAME=value $ echo ${NAME[*]:0:1} v $ but for macros (especially those coming from parsers)? [...] hmm.... thinking out loud. there are basically two syntactic options:
1) to use the new template function syntax
I had a look at the code yesterday, using Gergely's pointers from the other mail (thanks for that!), but one thing stopped me from doing some pointer arithmetics there myself - I wasn't sure how it'd work for unicode (i.e. multibyte) strings. Also pity that glib doesn't have a g_substr() :)
I wouldn't worry about unicode for now, we could call it $(cut), as Bazsi suggested, and document that it workes on bytes treams, and has no knowledge of unicode. For the vast majority of cases, that's good enough in my opinion. I couldn't think of a case where I would want to split unicode strings in template functions. (Also, there's g_strstr_len() in glib, which is almost like substr)
2) to continue extending our bash-like expansion syntax.
The 1) option would be something like:
$(cut -c 1-10 $NAME)
or
$(substr $NAME 1 10)
As for the syntax - I'd stick with substr <string> <offset> <length>, just like Perl, PHP, or MySQL do.
$(substr $NAME 1 10) is also easier to parse (and syslog-ng does that for us to begin with) than -c 1-10 (which would require a second parse), so I'd vote for the latter too.
The alternative would be to add really simple functions as an addition to the basic template syntax. We currently have the "default" values like this way:
${NAME:-default}
this results in "default" if $NAME is not-defined or empty.
The template function stuff is easier to write (as you can write plugins for that, and there's a whole framework to support it). The bash syntax-like stuff is more difficult to write as the template parser is manually coded, and each expansion mode has to be open-coded, although it has better performance (since we can avoid a copy of $NAME into a temporary buffer).
Efficiency is one of the factors I need to consider, so I'd love to see that ${macro:offset:len} working eventually, but for a starter, having it even as a (slower) template function would be neat too. Do you think syslog-ng could have both implemented $someday?
${macro:offset:len} sounds like a good candidate for a HOWTO! But, I'll knock up $(substr) first (though, due to work commitments, that'll be done later tonight, later than I've planned). I'll post the patch in this thread once it's ready. My offer still stands, nevertheless! -- |8]