How to git commit a single file/directory

If you are in the folder which contains the file

git commit -m 'my notes' ./name_of_file.ext

Your arguments are in the wrong order. Try git commit -m 'my notes' path/to/my/file.ext, or if you want to be more explicit, git commit -m 'my notes' -- path/to/my/file.ext.

Incidentally, Git v1.5.2.1 is 4.5 years old. You may want to update to a newer version (1.7.8.3 is the current release).

Use the -o option.

git commit -o path/to/myfile -m "the message"

-o, --only commit only specified files

Try:

git commit -m 'my notes' path/to/my/file.ext 

of if you are in the current directory, add ./ to the front of the path;

git commit -m 'my notes' ./path/to/my/file.ext