Figure out (using Git) whether a file was updated

Question

I have a few Git repositories that get updated automatically by a script. One of the tasks of the script is to run npm install for every repository (the repositories contain Node.js projects).

From time to time this results in an updated package-lock.json file, and I would like to commit it automatically if it was changed.

Of course I can simply run:

git add package-lock.json
git commit -m 'Update dependencies.'

But this fails, if the file was not updated: While git add simply does nothing and exits with return code 0, the git commit call fails with exit code 1. How can I do this in a way that this only happens if the file was actually updated?

In other words: If the file was not updated, I do not want the git add/git commit part to happen. How could I do this?

`git add && git commit -m `? See https://stackoverflow.com/questions/4510640/what-is-the-purpose-of-in-a-shell-command — evolutionxbox, Jul 04 '18 at 13:35
As said, this then returns with exit code `1`, which I do not want. — Golo Roden, Jul 04 '18 at 13:36
Yes, okay, this works as well – but this is pretty implicit, as it silences *any* error. — Golo Roden, Jul 04 '18 at 14:03

Nils Werner · Accepted Answer · 2018-07-04T13:46:51.383

3

You can use git diff --exit-code --quiet <filename> to check if the file was modified. If the returnvalue is 1, it was changed:

if ! git diff --exit-code --quiet package-lock.json ; then
    git add package-lock.json
    git commit -m 'Update dependencies.'
fi

That being said, there is no need to check the file beforehand and just running the lines

git add package-lock.json
git commit -m 'Update dependencies.' || true

will have the same effect, and a return value of 0

edited Jul 04 '18 at 13:46

answered Jul 04 '18 at 13:38

Nils Werner

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this is actually better than my proposal, as it doesn't involve using another executable to analyse output. I guess you can check for any file being modified with just `git diff --exit-code --quiet` right? – pqnet Jul 04 '18 at 13:50

score 1 · Answer 2 · answered Jul 04 '18 at 13:39

you can use git status --porcelain | grep . >/dev/null and check grep exit state to see if your working tree has modification

It works because git status --porcelain will output all changes, but no output in case the working tree is clean. grep . will exit success if it finds a match, fail if it doesn't, and . is regular expression for "anything"

HRK44 · Answer 3 · 2018-07-04T13:59:02.633

1

You can also use git diff <filename>, this will output the changes (if any) or nothing if no changes.

edited Jul 04 '18 at 13:59

answered Jul 04 '18 at 13:51

HRK44

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AFAIK `git show` would show the changes in the last commit, not in the current working tree compared to the head. `git diff` is probably the command you meant – pqnet Jul 04 '18 at 13:56
1

yes, meant git diff :D Nils werner answer is more complete tho – HRK44 Jul 04 '18 at 13:58

Figure out (using Git) whether a file was updated

3 Answers3