# Colorized Diffs

The oldest and most widely compatible method to get colorized diffs in
Fossil is to use its web UI:

    fossil ui --page '/vdiff?from=2024-04-01&to=trunk'

That syntax is admittedly awkward, and it doesn’t work where “from” is
the current checkout.  Fortunately, there are many other methods to get
colorized `diff` output from Fossil.


<a id="ui"></a>
## `fossil diff -b`

This produces a graphical diff in HTML format and sends it to the
user’s default web browser for viewing.



<a id="ui"></a>
## `fossil diff -tk`

You may be surprised to learn that the prior feature doesn’t use any of
the skinning or chrome from Fossil UI. This is because it is meant as a
functional replacement for an older method of getting colorized diffs,
“`fossil diff -tk`”. The feature was added after Apple stopped shipping
Tcl/Tk in macOS, and the third-party replacements often failed to work
correctly. It’s useful on other platforms as well.


<a id="git"></a>
## Delegate to Git

It may be considered sacrilege by some, but the most direct method for
those who want Git-like diff behavior may be to delegate diff behavior
to Git:

    fossil set --global diff-command 'git diff --no-index'

The flag permits it to diff files that aren’t inside a Git repository.


<a id="diffutils"></a>
## GNU Diffutils

If your system is from 2016 or later, it may include [GNU Diffutils][gd]
3.4 or newer, which lets you say:

    fossil set --global diff-command 'diff -dwu --color=always'

You might think you could give `--color=auto`, but that fails with
commands like “`fossil diff | less`” since the pipe turns the output
non-interactive from the perspective of the underlying `diff` instance.

This use of unconditional colorization means you will then have to
remember to add the `-i` option to `fossil diff` commands when producing
`patch(1)` files or piping diff output to another command that doesn’t
understand ANSI escape sequences, such as [`diffstat`][ds].

[ds]: https://invisible-island.net/diffstat/
[gd]: https://www.gnu.org/software/diffutils/


<a id="bat"></a>
## Bat, the Cat with Wings

We can work around the `--color=auto` problem by switching from GNU less
as our pager to [`bat`][bat], as it can detect GNU diff output and
colorize it for you:

    fossil set --global diff-command 'diff -dwu --color=auto'
    fossil diff -i | bat

In this author’s experience, that works a lot more reliably than GNU
less’s ANSI color escape code handling, even when you set `LESS=-R` in
your environment.

[bat]: https://github.com/sharkdp/bat


<a id="colordiff"></a>
## Colordiff

A method that works on systems predating GNU diffutils 3.4 or the
widespread availability of `bat` is to install [`colordiff`][cd], as
it is included in [many package systems][cdpkg], including ones for
outdated OSes. That then lets you say:

    fossil set --global diff-command 'colordiff -dwu'

The main reason we list this alternative last is that it has the same
limitation of unconditional color as [above](#diffutils).

[cd]: https://www.colordiff.org/

There is only one sub-feature of `git rebase` that is philosophically
compatible with Fossil yet which currently has no functional equivalent.
We [covered this and the workaround for its lack](#comsplit) above.

[3]: ./rebaseharm.md


<a id="cdiff"></a>
## Colorized Diffs

When you run `git diff` on an ANSI X3.64 capable terminal, it uses color
to distinguish insertions, deletions, and replacements, but as of this
writing, `fossil diff` produces traditional uncolored [unified diff
format][udiff] output, suitable for producing a [patch file][pfile].



There are [many methods](./colordiff.md) for solving this.




























Viewed this way, Fossil doesn’t lack colorized diffs, it simply has
*one* method where they *aren’t* colorized.

[cdpkg]: https://repology.org/project/colordiff/versions
[pfile]: https://en.wikipedia.org/wiki/Patch_(Unix)
[udiff]: https://en.wikipedia.org/wiki/Diff#Unified_format

The `--numstat` output is a bit cryptic, so we recommend delegating
this task to [the widely-available `diffstat` tool][dst], which gives
a histogram in its default output mode rather than bare integers:

    fossil diff -i -v --from 2020-04-01 | diffstat

We gave the `-i` flag in both cases to force Fossil to use its internal
diff implementation, bypassing [your local `diff-command` setting][dcset]
since the `--numstat` option has no effect when you have an external diff
command set.


If you leave off the `-v` flag in the second example, the `diffstat`
output won’t include info about any newly-added files.


[dcset]: https://fossil-scm.org/home/help?cmd=diff-command
[dst]:   https://invisible-island.net/diffstat/diffstat.html


<a id="btnames"></a>
## Branch and Tag Names

  chat.md {Fossil Chat}
  checkin_names.wiki {Check-in And Version Names}
  checkin.wiki {Check-in Checklist}
  childprojects.wiki {Child Projects}
  chroot.md {Server Chroot Jail}
  ckout-workflows.md {Check-Out Workflows}
  co-vs-up.md {Checkout vs Update}
  colordiff.md {Colorized Diffs}
  copyright-release.html {Contributor License Agreement}
  concepts.wiki {Fossil Core Concepts}
  contact.md {Developer Contact Information}
  containers.md {OCI Containers}
  contribute.wiki {Contributing Code or Documentation To The Fossil Project}
  css-tricks.md {Fossil CSS Tips and Tricks}
  customgraph.md {Theming: Customizing the Timeline Graph}

<li><a href="serverext.wiki">CGI Server Extensions</a></li>
<li><a href="checkin_names.wiki">Check-in And Version Names</a></li>
<li><a href="checkin.wiki">Check-in Checklist</a></li>
<li><a href="ckout-workflows.md">Check-Out Workflows</a></li>
<li><a href="foss-cklist.wiki">Checklist For Successful Open-Source Projects</a></li>
<li><a href="co-vs-up.md">Checkout vs Update</a></li>
<li><a href="childprojects.wiki">Child Projects</a></li>
<li><a href="colordiff.md">Colorized Diffs</a></li>
<li><a href="build.wiki">Compiling and Installing Fossil</a></li>
<li><a href="contribute.wiki">Contributing Code or Documentation To The Fossil Project</a></li>
<li><a href="copyright-release.html">Contributor License Agreement</a></li>
<li><a href="private.wiki">Creating, Syncing, and Deleting Private Branches</a></li>
<li><a href="customskin.md">Custom Skins</a></li>
<li><a href="custom_ticket.wiki">Customizing The Ticket System</a></li>
<li><a href="antibot.wiki">Defense against Spiders and Robots</a></li>