Fallback for diffFilter.interactive

[pylipp]

Hej, thanks for the amazing tool!
I have a question (about git configuration rather):
How can I have diffFilter.interactive configured in a way that it falls back to the default (colored) output when delta is not installed?

I tried

[interactive]
    diffFilter = delta --color-only --theme='Solarized (light)' || less -RFX

which in combination with git add -p has the non-colored output

sh: 1: delta: not found
Missing filename ("less --help" for help)
diff --git a/gitconfig b/gitconfig
index 46e391b..c301f89 100644
...

Maybe someone has a similar situation :)

[dandavison]

Hi @pylipp, I think the way to do this is with a shell script. This should work on Linux or MacOS but on Windows might need to be changed a little.

So what you'd do is create a file like this, for example saving it at ~/delta-with-fallback-to-less.sh and make it executable (chmod +x ~/delta-with-fallback-to-less.sh):

#!/bin/bash

if which delta > /dev/null 2>&1; then
    exec delta "$@"
else
    exec less -RFX
fi

Then in your ~/.gitconfig you'd do

[interactive]
    diffFilter = ~/delta-with-fallback-to-less.sh --color-only

I tested that quickly but let me know if you have any problems with it!

There are lots of variations one could make to that. For example see #19 (comment) regarding using the same delta options in the main pager command and in diffFilter.

[pylipp]

That does the trick, thanks (I'm on Linux)! Also for combining the two git config options.
I've substituted which by command -v because it's more portable.

What's the advantage of using exec? Not spawning the programs in another process?

[dandavison]

Good!

What's the advantage of using exec? Not spawning the programs in another process?

One reason is to ensure that the exit status is equal to the exit status of the delta process. If there were more lines in the script beyond the if statement (and without using bash's set -e) then there'd be a risk that a non-zero delta exit code would nevertheless result in a zero (success) exit code from the shell script, which could confuse the caller.

[pylipp]

TIL, thank you :)