SPUG: modify the include files depending up on instructions in it

[Sachin Chaturvedi]

i am having a file in all directories names as include.cfg
inside this file i am havinf a number of include statements like
#include "../comm.cfg"
#include "../ext.frg"
#include "../mem.cmd"
i have changed my script, which uses this file in such a way that i need to modify my file so that now it looks like this

#ifdef SYM
#include "$INCLUDE_DIR/ext.frg"
#else
#include "../include/ext.frg"
#endif
#ifdef SYM
#include "$INCLUDE_DIR/mem.cmd"
#else
#include "../include/mem.cmd"
#endif
this code is to be added for each include statements in the file. can any one help me with this how can i do. i am not a expert 
of perl, just learning things.