cat test.sh
#!/bin/sh -x
mkdir test_git
cd  test_git
git init
touch a
git add a
git commit -a -m 'initial commit'
git checkout -b 'new_branch'
echo test >a;
git commit -a -m 'test changed'
git checkout master
echo test2 >a
git checkout new_branch
git branch


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$ ./test.sh
+ mkdir test_git
+ cd test_git
+ git init
Initialized empty Git repository in /tmp/test_git/.git/
+ touch a
+ git add a
+ git commit -a -m 'initial commit'
[master (root-commit) db718c0] initial commit
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 a
+ git checkout -b new_branch
Switched to a new branch 'new_branch'
+ echo test
+ git commit -a -m 'test changed'
[new_branch c4037f9] test changed
 1 file changed, 1 insertion(+)
+ git checkout master
Switched to branch 'master'
+ echo test2
+ git checkout new_branch