How to resolve "Error: bad index – Fatal: index file corrupt" when using Git

This sounds like a bad clone. You could try the following to get (possibly?) more information:

git fsck --full

If the problem is with the index as the staging area for commits (i.e. .git/index), you can simply remove the index (make a backup copy if you want), and then restore index to version in the last commit:

On OSX/Linux/Windows(With Git bash):

rm -f .git/index
git reset

On Windows (with CMD and not git bash):

del .git\index
git reset

(The reset command above is the same as git reset --mixed HEAD)

You can alternatively use lower level plumbing git read-tree instead of git reset.

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If the problem is with index for packfile, you can recover it using git index-pack.

I had that problem, and I try ti fix with this:

rm -f .git/index
git reset

BUT it did not work. The solution? For some reason I had others .git folders in sub directories. I delete those .git folders (not the principal) and git reset again. Once they were deleted, everything worked again.

You may have accidentally corrupted the .git/index file with a sed on your project root (refactoring perhaps?) with something like:

sed -ri -e "s/$SEACHPATTERN/$REPLACEMENTTEXT/g" $(grep -Elr "$SEARCHPATERN" "$PROJECTROOT")

to avoid this in the future, just ignore binary files with your grep/sed:

sed -ri -e "s/$SEACHPATTERN/$REPLACEMENTTEXT/g" $(grep -Elr --binary-files=without-match "$SEARCHPATERN" "$PROJECTROOT")