[l2h] The latex behaviour of \externalref and \externallabels

Robert Petry Robert Petry <rpetry@scf.sk.ca>
Wed, 08 Mar 2000 16:21:03 -0600

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Hi again,
    Currently \externalref and \externallabels do nothing in a latex
document and hyperref produces ?? in dvi files when references are made
to external documents.  What I was wondering is if we could modify this
behaviour in html.sty so that latex could use these commands to produce
real references in the dvi file to labels, etc. in other documents.
(Where I work we've got several hundred-page documents which are
periodically released for which we would like references to each other
not only in the html docs but in the actual latex dvi files.)
    What I would suggest is the following:
1) modifying \externallabels from \externallabels{}{} to
\externallabels[ filename]{...}{...}
where filename is the pathname to the other document (either  / ...
/file  or  / ... /file.tex   ) from which the labels would be included
when latex-ing.  (For remote documents one would require a copy of the
.aux file locally.)   When latexing, the command would load the labels
from filename.aux, ignoring the other arguments, and when latex2html'ing
the filename optional argument would just be ignored.  Note a change in
html.perl to just ignore this optional argument would be required.

2) modifying \externalref{label} to actually produce a label reference
to such included external labels in the latex dvi file by default, and
add an optional argument (mirroring that of \hyperref) which would do
the following:

\externalref{label}           -->    does a \ref{label} in the latex
\externalref[ref]{label}      -->    does a \ref{label} in the latex
\externalref[page]{label}     -->    does a \pageref{label} in the latex
\externalref[pageref]{label}  -->    does a \pageref{label} in the latex
\externalref[no]{label}       -->    no output in the latex file
\externalref[noref]{label}    -->    no output in the latex file
\externalref[external]{label} -->    prints the label in the latex file

For latex2html \externalref would have the same behaviour it currently

To this end I wrote a style file (attached to this email) called
externlabels.sty (which must be included AFTER latex2html's html.sty if
that package is being used) which does two things.  It implements a
redefinition of \externalref as suggested above which works with my
version of latex2html.  i.e. html.perl ignores the optional argument
okay already.

Secondly the style file defines a command called
which includes labels from another document determined by filename as
discussed above so that they can be used in the current file when
latexing.  This command should go in the preamble.  It reads the .aux
file of the document whose labels are to be included. Though I could
have redefined \externallabels with an optional argument as I wanted to
above, html.perl no longer worked properly on it when running
latex2html.  For that reason I left such a redefinition of
\externallabels commented out in externlabels.sty . See the style file
itself for documentation on how to use the commands, etc.  Note that the
style file should work with latex2e regardless of whether one has
latex2html installed on the system.

What I'd like then, if the powers that be think my suggestion is a good
idea, is for html.sty to be changed so that \externalref and
\externallabels include these optional arguments. (Whether one should
put an \externlabels{filename} command in html.sty is debatable.)  As
well someone has to modify html.perl so that it handles the optional
argument correctly for \externallabels.  Perhaps an \externalpageref{}
command should also be defined to parallel \pageref. \externalpageref
would be the same as \externalref[page].

My tex code in externlabels.sty is really bizarre as I didn't know what
I was doing.  There must be another package out there for taking labels
out of other documents which is more sensible, which could be
implemented.  (For those of you who don't know, labels get placed in the
.aux file.  These must be read in and parsed for the \newlabel commands
which then must be executed in the current document.) If there is such a
package, someone could tell me about it.  Otherwise my bizarre code
could be revised and implemented.  It's got lots of documentation to
show the contortions I went through to trick TeX to do what I want.  My
main point was simply to pose the question of how latex external labels
ought to be implemented to comply with latex2html's usage, not to
demonstrate my lack of TeX ability to the world!

If all this has been discussed and I'm just doing this all the wrong
way, I'd appreciate it if someone would tell me how they work this.
(Placing all my manuals into one big (600+ page) manual or even
rewriting them as segments is not really an option I desire.  Our source
latex documents sit on VMS, I'm just using linux to convert them to

Thanks for listening,

--Robert Petry

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% This style file creates several commands to use labels from other
% latex files in the current document.
% The command
% \externlabels{filename}
% will take out all the labels in filename.aux so that they can be used in
% the current document just as though they had been created in that
% document.  It is preferable not to include the .tex extension on the
% filename.  If it is included AND there is a period anywhere else in the
% name before the extension (due say to a relative pathname) \externlabels
% will fail.
% To use the references, the commands \ref and \pageref could be used, but
% it is preferable to use the following \externalref command (also defined in
% this style package) because 1) it shows the labels are from other documents
% and  2) it makes the reference suitable for use by latex2html.
% \externalref[opt]{label}
% should be used where the optional parameter opt can be any of the
% following:
% \externalref{label}           -->    does a \ref{label} in the latex  file
% \externalref[ref]{label}      -->    does a \ref{label} in the latex file
% \externalref[page]{label}     -->    does a \pageref{label} in the latex file
% \externalref[pageref]{label}  -->    does a \pageref{label} in the latex file
% \externalref[no]{label}       -->    no output in the latex file 
% \externalref[noref]{label}    -->    no output in the latex file
% \externalref[external]{label} -->    prints the label in the latex file
% The name of \externalref has been chosen to mirror the latex2html command
% of the same name, which, provided the LATEX2HTML command \externallabels
% (note the difference with \externlabels above) has been put in the
% current document, will place hyperlinks to the other documents when the
% HTML docs are created. (It is for this reason \externalref[no/noref] are
% defined, because latex2html can use them.) The latex2html commands
% \externalref and \externallabels are defined in html.sty, so if that
% package is being used, then externlabels.sty must be included AFTER that
% package, otherwise \externalref will produce no output in the dvi file.
% (i.e. in html.sty \externalref is essentially what this package now
% defines \externalref[no].  Ultimately it would be desirable if
% \externalref were redefined in the html.sty package to be what it is
% defined here to be (if this revision is considered desirable.)  Note
% that externlabels.sty will be completely ignored by latex2html.
% As a final note, the latex2html command \externallabels{}{} could be
% redefined to have an optional argument which would be filename as above
% which would cause \externallabels[filename]{ ... }{ ... } to behave like
% \externlabels{filename} in latex.  This redefinition is found at the end of
% the file and commented out because the latex2html file html.perl would have
% to first be modified to handle (i.e. ignore) this optional argument. 
% This was written by Robert Petry on March 8, 2000 with limited
% knowledge of the TeXnology, so my apologies for the awkwardness. It
% should be revamped by someone who knows what they are doing!
% The code to define \externalref is essentially the same as that found in
% html.sty package included with latex2html to define \hyperref with a few
% of the arguments removed.
% The following (pseudo)command tells latex2html to ignore these
% definitions.  This is currently unnecessary since latex2html typically
% ignores style files for which it has no perl implementation, but we
% put this just to be safe.
% \externlabels code:
% This creates the command stripextension which takes the filename as
% either file or file.tex and returns file.  Note however it will get
% confused if there is more than one period in the name.
\def\basestripextension #1.#2\par{#1}
\def\stripextension#1{\basestripextension #1.tex\par}
% Create a command \ifneof to test when one is NOT at an end of file.
% There should be an easier way of doing this but it wasn't obvious.
\def\ifneof#1{\ifeof#1 \neofflagfalse \else \neofflagtrue \fi \ifneofflag}
% Next make a copy of the \newlabel command so that we can redefine
% \newlabel to a \dummyfunc function which just produces a \%.  This will
% allow for testing which lines are \newlabel lines in the .aux file since when
% \newlabel is defined as \dummyfunc, it will make \newlabel{...}{...}  appear
% as a \% which can be easily checked.  Note that \% cannot exist normally in
% an .aux file since it produces output and would flag an error.
% Any \%'s will be selected to be executed, but we'll redefine \newlabel back
% to its real definition first so that the labels get executed.  As a final
% note we actually have to check for "\% " because the space gets added
% due to the carriage return at the end of each line in the aux file.
% We define \dummyfunccontents to be the command "\% ".
\def\dummyfunccontents{\% }
% Now the actual command itself.
% Modify the use of the @ symbol so that it won't mess up our program
% when we read in commands which include that symbol which Latex doesn't
% like.
% First try opening the file putting on the extension.
% If this failed, try opening the file stripping off the extension.
% File not found warning if not found.
  \message{Externlabels Warning: Auxilliary file of #1 not found.      }
  \message{If you are using a complicated filename with periods in it, }
  \message{don't use a filename extension in the externlabels command. }
  \message{Also make sure that #1 has been latex'd. External references}
  \message{to #1 will not be included in this pass.                    }
    \read0 to\inline
    % Now get the line's value.  If it's a \label it becomes "\% "
    % If it's a "\% " (i.e. a label) put \newlabel back and execute it.
% Return @ symbol.
% \externref code taken almost entirely from \hyperref definition
% in html.sty
% avoid possible confict with previous definition

 \else\typeout{*** unknown option \next\space to  externalref ***}

% \externallabels code
% The following lines of tex redefine the \externallabels command
% contained in the html.sty package of latex2html to have an optional
% first argument which is the location of external labels to be
% inserted in the latex document.  It just passes the option through
% \externlabels above so see that for details.  Currently the
% redefinition is commented out because html.perl in the latex2html package
% must be modified so that it ignores this latexonly optional argument
% properly. Hence don't use this command yet. If this command is
% implemented remember to change the warning above from externlabels to
% externallabels.
% \def\next{\newcommand}
% \def\next{\renewcommand}

% The following is a pseudo command for latex2html - leave it in.