modifying system calls
 

i just wanted to know can we make some change in system call used to open a file. i.e how it searches for contents of file. i.e when we try to open a file in any editor what actions are actually taken.

well when you open a file you just give it argument of file path name in the form of a character string and a flag for truncate, append, create. returned you get a file descripter and you can do anything you like with it. File descripters remember their place in the file but there is a call lseek you can use to jump around to positions off_t offset from the beginning if you like.

you mention editor.
editors can use a variety of wrapped methods like from a toolkit or something to access a file or can use syscalls directly.

thanx can u pl tell me which files are actually loaded when i type vi on the command prompt

that would be the executable file vi
most likely /usr/bin/vi