what is mod_unique_id...how can we install it ???????

what is this error code ?

[root@fruits apache2]# /usr/sbin/apxs -cia modsecurity.c
/bin/sh /usr/lib/apr/build/libtool --silent --mode=compile gcc -prefer-pic -O2 -g -pipe -m32 -march=i386 -mtune=pentium4 -DAP_HAVE_DESIGNATED_INITIALIZER -DLINUX=2 -D_REENTRANT -D_GNU_SOURCE -pthread -I/usr/include/apr-0 -I/usr/include/httpd -c -o modsecurity.lo modsecurity.c && touch modsecurity.slo
In file included from modsecurity.h:37,
from modsecurity.c:17:
msc_pcre.h:18:18: pcre.h: No such file or directory
modsecurity.c: In function `is_response_status_relevant':
modsecurity.c:316: error: `PCRE_ERROR_NOMATCH' undeclared (first use in this function)
modsecurity.c:316: error: (Each undeclared identifier is reported only once
modsecurity.c:316: error: for each function it appears in.)
apxs:Error: Command failed with rc=65536

Apache's documentation is all online.

As to the error, "msc_pcre.h:18:18: pcre.h: No such file or directory", it means that you are missing the requisite header files needed to compile. Reference the documenation (usually and INSTALL or README file) to see what you need to install first.