The following is relevant when working with documents spread over many files:
grep, search and
query-replace on all files which are part of a
multifile document.TeX-master for AUCTeX or
tex-main-file for the standard Emacs LaTeX mode)
containing the name of the master file. For example, to set
the file variable TeX-master, include something
like the following at the end of each TeX file:
%%% Local Variables: ***
%%% mode:latex ***
%%% TeX-master: "thesis.tex" ***
%%% End: ***
AUCTeX with the setting
(setq-default TeX-master nil)
will actually ask you for each new file about the master file and insert this comment automatically. For more details see the documentation of the AUCTeX (see Multifile), the documentation about the Emacs (La)TeX mode (see TeX Print) and the Emacs documentation on File Variables (see File Variables).