Why doesn't git recognize that my file has been changed, therefore git add not working

I had a problem where once upon a time I set the git index to 'assume unchanged' on my file.

You can tell git to stop ignoring changes to the file with:

git update-index --no-assume-unchanged path/to/file

If that doesn't help a reset may be enough for other weird cases.

In practice I found removing the cached file and resetting it to work:

git rm --cached path/to/file
git reset path/to/file

The git rm --cached means to only remove the file from the index, and reset tells git to reload the git index from the last commit.

Check your .gitignore file. You may find that the file, or extension of the file, or path to the file you are trying to work with matches an entry in .gitignore, which would explain why that file is being ignored (and not recognized as a changed file).

This turned out to be the case for me when I had a similar problem.

Sounds crazy, but sometimes you are not in the right repo even though you think you are. For example, you may have moved the parent directory, but forgot to switch repos in your text editor. Or vice versa: you're in the right repo in the text editor but the wrong repo in command line. In the first situation, you make your edits in the right file but it's not the same folder that's open in your command line, so it's actually the wrong file. In the second situation, you actually did edit the right file, but your command line git won't recognize the change because you're not in the correct directory on the command line.

Like it was already discussed, the files were probably flagged with "assume-unchanged", which basicly tells git that you will not modify the files, so it doesnt need to track changes with them. However this may be affecting multiple files, and if its a large workspace you might not want to check them all one by one. In that case you can try: git update-index --really-refresh

according to the docs:

Like --refresh, but checks stat information unconditionally, without regard to the "assume unchanged" setting.

It will basicly force git to track changes of all files regardless of the "assume-unchanged" flags.

well we don't have enough to answer this question so I will give you several guesses:

1) you stashed your changes, to fix type: git stash pop

2) you had changes and you committed them, you should be able to see your commit in git log

3) you had changes did some sort of git reset --hard or other, your changes may be there in the reflog, type git reflog --all followed by checking out or cherry-picking the ref if you ever do find it.

4) you have checked out the same repo several times, and you are in the wrong one.