如何在Shell脚本中获取git diff命令的output

Question

I am trying to perform Git diff in two branches with the same file. I want to get the difference of two files.

• If there is a fatal error
• If there is a difference/ not matched
• If there is NO difference/ matched

I tried saving the command in a variable to get the result. Example: GIT_DIFF=$(git diff RB_202005:/test.txt RB_202006:/test.txt) and then printing the variable (Example: echo $GIT_DIFF) but nothing is being returned.

Answer 1

Since you are only interested in the cases "no diff", "diff", "error", I would run a

git diff --exit-code --quiet .....

--exit-code sets the exit code in the way the normal diff would do.

--quiet suppresses the output.

If the exit code is 0, you don't have differences.

If the exit code is 1, you have differences.

If the exit code is 2 or 128, you have fatal errors.

UPDATED As the OP pointed out in the comment, git-diff --exit-code produces status code 128, if the file to be compared does not exist. According to the man-page, it should produce the same exit code as the standard diff , which would be 2. Hence it is best to treat any exit code larger than 1 as standard error. This would also catch the case that git itself is not found (in which case the shell would likely report exit code 127).

Answer 2

This would not always work with the new (Git 2.30, Q1 2021) git diff -I , should you want to ignore a diff pattern.

" git diff -I<pattern> -exit-code ^{( man )} " should exit with 0 status when all the changes match the ignored pattern, but it didn't.

See commit 50f0439 (16 Dec 2020) by Junio C Hamano ( gitster ) .
^{(Merged by Junio C Hamano -- gitster -- in commit 59fcf74 , 18 Dec 2020)}

diff : correct interaction between --exit-code and -I<pattern>

Just like " git diff -w --exit-code " ^{( man )} should exit with 0 when ignoring whitespace differences results in no changes shown, if ignoring certain changes with " git diff -I<pattern> --exit-code ^{( man )} " result in an empty patch, we should exit with 0.

The test suite did not cover the interaction between " --exit-code " and " -w "; add one while adding a new test for " --exit-code " + " -I ".