Tracking Changes in Latex – The Easy Way

February 17, 2016 (Last Modified: March 14, 2020)

Latex has many advantages in comparison to WYSIWYG word processors such as Microsoft Word or Libre Office. Being a text based markup language, Latex allows distraction free writing in a large selection of editors, it scales easily also for large projects with hundreds or thousands of references and images within the text and it produces very clean layouts, which can be exchanged simply by using different document classes. If you use a version control system such as git or svn, also versioning becomes very convenient, every change can be seen in the text file as a simple diff.

Although I am a big fan of latex, there are some things where other processors such as Word do have their advantages as well. Tracking changes is such an advantage, which is solved very nicely and intuitively. Source code management tools such as git and svn can produce a diff of the file and highlight changes, but the changes are not rendered in the document. Tracing changes in a Latex source file is not comfortable, especially if people should be able to see where changes have been made in a document, who are not familiar with the Latex source.

Installing latexdiff

The Perl tool latexdiff provides this missing feature and creates a Latex file as output, which contains the changes made between two revisions of a file. In addition the changes are highlighted in a similar fashion as in graphical text processors. Install the tool with the following apt command:

sudo apt-get install latexdiff

This provides the following tools for various source code management systems, as indicated by the suffix.

latexdiff latexdiff-cvs latexdiff-fast latexdiff-git latexdiff-rcs latexdiff-svn latexdiff-vc

Tracing Changes

After installing the software package, you can start comparing different revisions of the same file. Simply use the following command to highlight changes between two files. Note that this command creates a new Latex document as output, which you then need to compile in order to have a readable PDF with the changes.

# Generate diff with tracked changes
latexdiff Document_Version1.tex Document_Version2.tex > Document_Changes_V1_v2.tex
# Compile the Latex document
pdflatex Document_Changes_V1_v2.tex

This gives the following output, where the blue content has been added from one version to another and the red content has been deleted.

Using Revision Control

If you manage your Latex source with git or any other SCM tool anyways, you can use the same tool for comparing different revisions. Lets have a look at previous revisions in the git log:

stefan@stefan-Linux:~/Gitlab-Workspace/LatexTest$ git log
commit fc894678144569ace27776f82f230cfce0f1f017
Author: Stefan Pröll <sproell@sba-research.org>
Date:   Wed Feb 17 18:40:37 2016 +0100

    revision 2

commit 76bacf74d21f486daa4404a9bf16d2bfd634c38e
Author: Stefan Pröll <sproell@sba-research.org>
Date:   Wed Feb 17 18:36:41 2016 +0100

    revision 1

commit 641053bee12b9e9ecd8312c82925f5a962e5d65a
Author: Stefan Pröll <sproell@sba-research.org>
Date:   Wed Feb 17 17:45:17 2016 +0100

    mandrill init

Suppose we want to track the changes between revision 1 and revision 2, you can use the appropriate lateydiff variant to compare the revisions with eachother.

latexdiff-git -r fc894678144569ace27776f82f230cfce0f1f017 -r 76bacf74d21f486daa4404a9bf16d2bfd634c38e Document.tex

Note that in this case we provide the commit hash for git. This tool automatically writes the output in a new file denoted with the names of the two commit hashes that we provided. In the case of Subversion, you can also provide the revision id.

Limitations

It is important to understand that the Latex tool only considers changes in the printable text. This entails that if you change a picture or even replace an image with a new file (having a new file name), this will not be highlighted.