Why "git reset <file>" returns 1?

Question

Assume that foo.txt is in the index.

Why doing:

git reset foo.txt

returns 1:

$ echo $?
1

?

Answer 1

git reset foo.txt returns zero when foo.txt has no unstaged changes after the reset, and one when it does.

This allows scripting code to determine if the file in question has been modified since the last commit.