Check out the Exchange, I have done 3 expressions:
regexMatch, isRegexMatch and regexReplace. It is based on the BOOST REGEX lib. There are 3 options of engine: POSIX, POSIX extended and PERL regex.
It is only available for Windows for now, but I am working on compiling the linux version right now.
I tested at a certain extend. If anyone finds some bugs or wants some extra, drop me a line.
There is more explaination in the zip bundle.

Now my question, how can we add help for expressions without modifying the $HFS/houdini/help/exprhelp coming with Houdini distribution? Like for any other DSO. in $HOME/houdiniXXX/config/help for example.
Cheers
Le Monkey

Le_monkey_butt
Now my question, how can we add help for expressions without modifying the $HFS/houdini/help/exprhelp coming with Houdini distribution? Like for any other DSO. in $HOME/houdiniXXX/config/help for example.
Cheers
Le Monkey

Houdini looks for an ‘exprhelp’ file at every HOUDINI_PATH location. So just add stuff to it (in the correct format), and when you do

exhelp <hdkexpression>

the correct help will show.

On a related note, I recommend that rather than making exprhelp one gigantor file, compile it from a bunch of little .funchelp files, i.e. for each .func file, make a corresponding .funchelp, and then just concatenate all of them into the ‘exprhelp’ file. Then in your case, you can have one extra .funchelp that contains the help for the hdk expressions you just wrote.

Cheers
That is what I thought but I may have done a mistake at one point.
Regarding the splitting of the funchelp file, I aggree.

Nice one!