threads / discuss / 45469

Question: xdiff and "pretty" (human readable) diff output

Subject: Question: xdiff and "pretty" (human readable) diff output

## tl;dr

3 messages between Mar 22, 2017 and Mar 22, 2017.

replies: 2people: 2as markdown or json

matthew@giassa.net· Mar 22, 2017, 19:23 UTC · lore

Good day,

I have a question with respect to how git generates "pretty" (ie: human readable) unified diffs. It's to my understanding that git uses its own (simplified/minimized) fork of libxdiff, simply referred to as "xdiff" [1]. Which tool/library is used to take the xdiff output and generate the human-readable equivalent that is rendered to the console? I have a program that I'm maintaining that currently tracks changes to a couple of "sandboxed" files, and I wanted to add a simple console UI that periodically shows the changes to the files over time and/or dumps the "pretty diff" to syslog.

Thank you.

1. "Use a *real* built-in diff generator Â· git/git@3443546",
   <https://github.com/git/git/commit/3443546f6ef57fe28ea5cca232df8e400bfc3883>,
   Accessed 2017-03-22

--Matthew

Stefan Beller· Mar 22, 2017, 19:43 UTC · re: matthew@giassa.net · lore

Re: Question: xdiff and "pretty" (human readable) diff output

On Wed, Mar 22, 2017 at 12:23 PM,  <matthew@giassa.net> wrote:

Show 6 quoted lines

> Good day,
>
> I have a question with respect to how git generates "pretty" (ie: human
> readable) unified diffs. It's to my understanding that git uses its own
> (simplified/minimized) fork of libxdiff, simply referred to as "xdiff"
> [1].

correct.

> Which tool/library is used to take the xdiff output and generate
> the human-readable equivalent that is rendered to the console?

Git itself. Have a look at diff.c (it's only 5k lines of code ;)

Maybe start with fn_out_consume which is a callback (for xdiff) that is responsible for pretty printing the output, i.e. transforming the output of xdiff according to Gits configuration.

Show 5 quoted lines

> I have a
> program that I'm maintaining that currently tracks changes to a couple
> of "sandboxed" files, and I wanted to add a simple console UI that
> periodically shows the changes to the files over time and/or dumps the
> "pretty diff" to syslog.

> over time

So you could use cron for that?

>  "pretty diff" to syslog.

So you want to modify the "pretty diff"? Maybe that can be archived by a custom format (see the git *log* man page) and doesn't require hacking.

Thanks, Stefan

matthew@giassa.net· Mar 22, 2017, 19:47 UTC · re: Stefan Beller · lore

Re: Question: xdiff and "pretty" (human readable) diff output

* Stefan Beller <sbeller@google.com> [2017-03-22 12:43:41 -0700]:

Show 37 quoted lines

>On Wed, Mar 22, 2017 at 12:23 PM,  <matthew@giassa.net> wrote:
>> Good day,
>>
>> I have a question with respect to how git generates "pretty" (ie: human
>> readable) unified diffs. It's to my understanding that git uses its own
>> (simplified/minimized) fork of libxdiff, simply referred to as "xdiff"
>> [1].
>
>correct.
>
>> Which tool/library is used to take the xdiff output and generate
>> the human-readable equivalent that is rendered to the console?
>
>Git itself. Have a look at diff.c (it's only 5k lines of code ;)
>
>Maybe start with fn_out_consume which is a callback (for xdiff)
>that is responsible for pretty printing the output, i.e. transforming the
>output of xdiff according to Gits configuration.
>
>> I have a
>> program that I'm maintaining that currently tracks changes to a couple
>> of "sandboxed" files, and I wanted to add a simple console UI that
>> periodically shows the changes to the files over time and/or dumps the
>> "pretty diff" to syslog.
>
>> over time
>
>So you could use cron for that?
>
>>  "pretty diff" to syslog.
>
>So you want to modify the "pretty diff"?
>Maybe that can be archived by a custom format
>(see the git *log* man page) and doesn't require hacking.
>
>Thanks,
>Stefan

Thank you Stefan. This provides me with everything I need.

Cheers!

-- 
Matthew Giassa
e: matthew@giassa.net