For "git diff" is there a -U option to show the whole file?

Question

I need to generate a full-context git diff programmatically for a web ui.

A CLI for generating a full-context diff was covered in questions:

The prevalent answer is something like git diff -U99999

With a -U / --unified option with a ridiculously high threshold (e.g. 999,999), doing git diff -U999999:

Makes me suspect that there could be a performance hit
Even worse, it's a correctness issue if my file is larger than 1M lines

Is there a -U option to show the whole file?

Another option is `git diff -U\`wc -l |cut -f 1 -d" "\` HEAD^ ` but you need to run `wc` on the longer version of the file — kdopen, Jul 16 '15 at 16:57
Possible duplicate of [How to get git diff with full context?](https://stackoverflow.com/questions/13627598/how-to-get-git-diff-with-full-context) — rjmunro, Jul 31 '19 at 09:39

score 9 · Accepted Answer · answered Mar 04 '15 at 04:15

9

If you just use a large number with -U, you could choose the large number to be the point at which your application can't handle displaying such a large file (diff).

it's a correctness issue if my file is larger than 1M lines

And to address this issue, you can check the output for more than one @@ ... @@ line to determine whether it's complete — this allows you to avoid silently giving a wrong number.

answered Mar 04 '15 at 04:15

Kevin Reid

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8

Experimentally, I found `git diff -U999999999999999999` gave `Segmentation fault (core dumped)`. However, one digit less, `-U99999999999999999`, worked. Also, adding two or more digits to the first command, `-U999999999999999999999999`, caused it to behave as though the option had actually been `-U0`. – Mr. Lance E Sloan May 03 '16 at 19:47
"-U 999999999" for current OS X (more 9s will fail) – lilalinux Jul 14 '23 at 12:23

score 1 · Answer 2 · answered Feb 27 '15 at 23:14

Frankly, the best option is to use git difftool rather than vanilla git diff. To see which tools your version of git supports, enter

git difftool --tool-help

which, with my version (2.3.0), shows the following

$ git difftool --tool-help
'git difftool --tool=<tool>' may be set to one of the following:
        araxis
        gvimdiff
        gvimdiff2
        gvimdiff3
        meld
        vimdiff
        vimdiff2
        vimdiff3

The following tools are valid, but not currently available:
        bc
        bc3
        codecompare
        deltawalker
        diffmerge
        diffuse
        ecmerge
        emerge
        kdiff3
        kompare
        opendiff
        p4merge
        tkdiff
        xxdiff

I usually use meld, but that's just a personal preference. git difftool takes the same arguments as git diff plus a few to help with the process (I find -y useful to prevent the prompts when moving from one file to the next).

To check out the changes introduced by a specific commit, for example, you can use

git difftool -y -t meld 08f0f82^..08f0f82

obviously replacing 08f0f82 with the correct SHA-1.

My biggest complaint is that it launches the tool for each modified file in sequence (hence specifying the -y option).

If you only wanted to examine the changes to a particular file in that commit, you can just add the filename to the command line.

git difftool -y -t meld 08f0f82^..08f0f82 myfile.c

Obviously, this is for interactive use - not for scripting

I need this for accessing programmatically from a web ui. Sorry did not make it clear right away. — Aleksandr Levchuk, Mar 03 '15 at 18:48
This answer doesn't even address the question of getting a full-context diff without lines removed. — Mr. Lance E Sloan, May 03 '16 at 19:51

For "git diff" is there a -U option to show the whole file?

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