Utility to Strip Comments from LaTeX Source

Question

I've a LaTeX source.
I'm ready %for submission
%But first I would like
to strip its comments.

So I hope there are
100\% auto
ways to get this done.

\begin{comment}
   Because there are subtle ways to mess it up.
\end{comment}

Is there a utility which will eliminate all these comments?

Yes, I could do it by hand, but that seems needlessly laborious, has the potential for mistakes, and makes maintenance difficult. I could also use sed, but there's a potential for mistakes. Besides, it is an axiom of the whole GNU/Linux thing that if you can think of it, someone's probably already made a utility for it.

Answer 1

I'm not sure how to do this. So, I'm posting a new solution. The code I posted yesterday will eat comments from within a verbatim environment.

Here's a new example file to be cleaned:

I've a LaTeX source.
I'm ready %for submission
%But first I would like
to strip its comments.

So I hope there are
100\% auto
ways to get this done.

\begin{comment}
   Because there are subtle ways to mess it up.
\end{comment}

\begin{verbatim}
        next two lines should not be lost
        % don't lose this line
% this line should stay too
\end{verbatim}

According to the verbatim package documentation verbatim and comment environments should not be nested. The following code (similar to what I posted yesterday) will not eat commented lines that appear within a verbatim environment.

Here is the corrected Perl code:

#!/usr/bin/perl
use strict 'vars';
&MAIN(@ARGV);
sub MAIN {
   my ($filehandle) = @_;

   open FILE, "<$filehandle";
   my @doc = <FILE>;
   close FILE;

   &removeComments(\@doc);

   foreach my $line ( @doc ){
      print $line;
    }

   return 1;
}

sub removeComments {
   my ($docarray) = @_;

   my $isCommentEnvironment  = "no";
   my $isVerbatimEnvironment = "no";

   my @newdoc;

   foreach my $line ( @{$docarray} ){
      $isVerbatimEnvironment = "yes" if ( $line =~ /^\\begin{verbatim}/ );
      $isCommentEnvironment  = "yes" if ( $line =~ /^\\begin{comment}/ );
      if ( ($isVerbatimEnvironment eq "no") && ($isCommentEnvironment eq "no") ){
     next if ($line =~ /^%/);
     ## Temporarily replace "%" that you want to keep with a dummy string
     ## that does not appear elsewhere in your document.  Then, remove remainder
     ## of lines that still contain "%".
     if ( $line =~ /\\%/){
        $line =~ s/\\%/TMP::PERCENT/g;
        $line =~ s/%.*//;
        $line =~ s/TMP::PERCENT/\\%/g;
      } else {
         $line =~ s/%.*//;
       }
     push @newdoc, $line;
       }
      push @newdoc, $line if ( $isVerbatimEnvironment eq "yes" );

      $isVerbatimEnvironment = "no" if ( $line =~ /^\\end{verbatim}/ );
      $isCommentEnvironment  = "no" if ( $line =~ /^\\end{comment}/ );
    }

   @{$docarray} = @newdoc;
   return 1;
 }  

Answer 2

The following Perl script should do the trick: it expects to receive the name of the file you want stripped of comments and prints to console the modified document.

#!/usr/bin/perl
use strict 'vars';
&MAIN(@ARGV);
sub MAIN {
   my ($filehandle) = @_;
   open FILE, "<$filehandle";
   my @doc = <FILE>;
   close FILE;
   &removeComments(\@doc);

   foreach my $line ( @doc ){
      print $line;
    }
   return 1;
}
sub removeComments {
   my ($docarray) = @_;
   my $isCommentEnvironment = "no";
   my @newdoc;

   foreach my $line ( @{$docarray} ){
      $isCommentEnvironment = "yes" if ( $line =~ /^\\begin{comment}/ );
      if ( $isCommentEnvironment eq "no" ){
     next if ($line =~ /^%/);
     ## Temporarily replace "%" that you want to keep with a dummy string
     ## that does not appear elsewhere in your document.  Then, remove remainder
     ## of lines that still contain "%".
     if ( $line =~ /\\%/){
        $line =~ s/\\%/TMP::PERCENT/g;
        $line =~ s/%.*//;
        $line =~ s/TMP::PERCENT/\\%/g;
      } else {
         $line =~ s/%.*//;
       }
     push @newdoc, $line;
       }
      $isCommentEnvironment = "no" if ( $line =~ /^\\end{comment}/ );
    }

   @{$docarray} = @newdoc;
   return 1;
 }  

The only thing I'm uncertain about is any contraints on using \begin{comment} and \end{comment}. For example, I don't know whether---like with the verbatim environment---you are restricted on what else may appear on those lines.