gistfile1.txt

[~/desktop/test] $ echo "hi" > file
[~/desktop/test] $ git init
Reinitialized existing Git repository in /Users/ivanruizmonjo/Desktop/test/.git/
[~/desktop/test] $ git add file
[~/desktop/test] $ git commit -am "Initial commit"
[master (root-commit) bd5201b] Initial commit
 1 file changed, 1 insertion(+)
 create mode 100644 file
[~/desktop/test] git:master $ git branch -a
* master
[~/desktop/test] git:master $ git checkout -b newBranch
Switched to a new branch 'newBranch'
[~/desktop/test] git:newBranch $ echo "modified by newBranch" > file
[~/desktop/test] git:newBranch $ git checkout master
M	file
Switched to branch 'master'
[~/desktop/test] git:master $ cat file
modified by newBranch
[~/desktop/test] git:master $