git commit-a

CommandNew filesChanged filesDeleted files
Alice/> git init
Initialized empty Git repository in /home/rene/github/github/git-internals/repos/commit-a/Alice/.git/
snap no: 1
Alice/> echo foo > foo.txt
snap no: 2
Alice/> git add .
snap no: 3
Alice/> git commit -m "foo"
[master (root-commit) 0349c36] foo
 1 file changed, 1 insertion(+)
 create mode 100644 foo.txt
snap no: 4
Alice/> echo foo foo > foo.txt
snap no: 5

Commiting without specifying -a will only commit files that were explicitely added

Alice/> git commit -m "foo foo ?"
On branch master
Changes not staged for commit:
	modified:   foo.txt

no changes added to commit
snap no: 6
Alice/> git status
On branch master
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   foo.txt

no changes added to commit (use "git add" and/or "git commit -a")
snap no: 7

Nothing was commited

This time, the commit goes along with the -a flag, the file will be commited

Alice/> git commit -a -m "foo foo"
[master 7027aab] foo foo
 1 file changed, 1 insertion(+), 1 deletion(-)
snap no: 8
Alice/> git status
On branch master
nothing to commit, working directory clean
snap no: 9