One might want this so as to automatically generate a page header or footer recording what file is being processed. It’s not easy…
TeX retains what it considers the name of the job, only, in
the primitive \jobname; this is the name of the file first
handed to TeX, stripped of its directory name and of any extension
(such as tex). If no file was passed (i.e., you’re using
TeX interactively), \jobname has the value texput
(the name that’s given to log files in this case).
This is fine, for the case of a small document, held in a single file;
most significant documents will be held in a bunch of files, and
TeX makes no attempt to keep track of files input to the
job. So the user has to keep track, himself — the only way
is to patch the input commands and cause them to retain details of the
file name. This is particularly difficult in the case of Plain TeX,
since the syntax of the \input command is so peculiar.
In the case of LaTeX, the input commands have pretty regular
syntax, and the simplest patching techniques can be
used on them. (Note that LaTeX’s \input command is itself a
patch on top of the Plain TeX command. Our patches apply to the
LaTeX version of the command, which is used as \input{file})
%%
%% \def\ThisFile{\jobname}
%% \let\OldInput\input
%% \renewcommand{\input}[1]{%
%% \renewcommand{\ThisFile}{#1}%
%% \OldInput#1%
%% }
%%
%%
%% \documentclass{article}
%% ... (macros above)
%% \begin{document}
%% \input{preamble}
%%
%% \input{postamble}
%% \end{document}
%%
%%
%% \def\ThisFile{\jobname}
%% \newcounter{FileStack}
%% \let\OrigInput\input
%% \renewcommand{\input}[1]{%
%% \stackinput{#1}{\OrigInput}%
%% }
%% \newcommand{\stackinput}[2]{%
%% \stepcounter{FileStack}%
%% \expandafter\let
%% \csname NameStack\theFileStack\endcsname
%% \ThisFile
%% \def\ThisFile{#1}%
%% #2#1%
%% \expandafter\let\expandafter
%% \ThisFile
%% \csname NameStack\theFileStack\endcsname
%% \addtocounter{FileStack}{-1}%
%% }
%%
%%
%% \let\OrigInclude\include
%% \renewcommand{\include}[1]{%
%% \stackinput{#1}{\OrigInclude}%
%% }
%%
It is possible to keep track of the name of the file currently being processed, but it’s surprisingly difficult (these FAQs offered code, for a long time, that just didn’t work in many cases).
The currfile package provides a regular means of keeping
track of the details of the current file (its name in
\currfilename, directory in \currfiledir, as well as the
file ‘base’ name (less its extension) and its extension).
Currfile does this with the help of a second package,
filehook, which spots file operations that use \input,
\InputIfFileExists and \include, as well as package and
class loading.
The FiNK (“File Name Keeper”) package keeps track of the
file name and extension, in a macro \finkfile. FiNK is
now deprecated, in favour of currfile, but remains available
for use in old documents.
%%
%% \def\striptexext#1.tex{#1}
%% ...
%% \edef\ThisFile{\expandafter\stripext\finkfile}
%%
The FiNK bundle includes a fink.el that provides
support under emacs with AUC-TeX.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=filename