Sometimes I run git add . and big files that weren't supposed to get added are added. How can I see which files were added without commiting? And how to 'un-add' those files or all files at once so I can fix the .gitignore?
(Disclaimer : none of the commands below modifies your changes in files, all this is about what's staged or not)
How to...
...display the full list of what's staged at this point. (doc for diff --staged)
git diff --staged --name-only
..."un-add" (unstage) one file
git reset -- path/to/file
...or similarly, unstage a directory with everything in it
git reset -- path/to/dir/
...unstage everything (example in the doc)
git reset
...and last but not least, the "unstage wizard"! (interactive unstaging, which goes chunk by chunk like it does for git add -p)
git reset -p
Finally, about fixing your .gitignore, take a look at git check-ignore -v <path> to know specifically which .gitignore file ignores your path.