`git diff`doesn't show changes you have in work tree relative commit -

i found image graphically show work of diff command. http://images.abizern.org.s3.amazonaws.com/365git/march10/gitdiffsimple.png

git diff head 

show changes have in working tree relative head, if run script

mkdir test_git cd test_git git init echo 'one_file.txt' >> one_file.txt git add . git commit -m "my first commit" echo 'second_file.txt' >> second_file.txt git diff head 

then diff don't show diff of seconrd_file.txt. why?

the git diff command provides relative difference between current working directory or current index respect head. in example above creating new file have not added index or committed it. in terms of head new file not exist , not tracked there no difference. staging file in index git add second_file.txt introduce new file repository , yield diff when executing git diff --cached command.

the process of tracking changes explained in detail in freely available in pro git - 2.2 git basics.