How to use regular expressions in StreamDevice.

First, you need the PCRE library.
If it is already installed for your (Linux) system (try: rpm -ql pcre),
set the following variables in your RELEASE file:
PCRE_INCLUDE=<direcrory of pcre.h>
PCRE_LIB=<direcrory of libpcre.so>

For vxWorks, Windows and others you're probably out of luck here.
In that case, download the PCRE package from www.pcre.org and
epics.web.psi.ch/software/streamdevice/pcre/Makefile and compile
PCRE as an EPICS application. Use the variable PCRE in your RELEASE file
to define the location of this application.

If either PCRE or PCRE_INCLUDE or PCRE_LIB are set in the RELEASE file,
StreamDevice is automatically build with regular expression support.

The syntax is %/regexp/. It can only be used in input. It returns the
next string that matches the regexp. Anything before this string is skipped.

To use sub-expressions use %.n/rexexp/ where n is a number from 1 to 9
to match the n-th sub-expression. 

It is possible to limit the input length to the match algorithm like
%m/regexp/ where m is the maximal length.

Example:
in "%100.1/<title>(.*)<\/title>/";
This searches the next 100 bytes and returns the string bewteen
<title> and </title>. Any input before <title> is skipped. Any input
after </title> is left in the buffer (and can by matched by other formats).
Note that the / in </title> must be escaped.

See regexp.cmd, regexp.proto, regexp.db for a working example.