~/tmp/git $ git --version
git version 1.8.3.1
~/tmp/git $ bash --version
GNU bash, version 4.2.46(1)-release (x86_64-redhat-linux-gnu)

~/tmp/git $ git init
Initialized empty Git repository in /home/pp/tmp/git/.git/
~/tmp/git $ echo 1 > test
~/tmp/git $ git add test
~/tmp/git $ git commit -m 'line 1
> line 2
> line 3'
[master (root-commit) 10fcfb9] line 1 line 2 line 3
 1 file changed, 1 insertion(+)
 create mode 100644 test
~/tmp/git $ git show
commit 10fcfb96be4be214a5211fb9d1771bc9dfc2bd62
Author: pp <pp@pp.pp>
Date:   Mon Jul 4 19:28:32 2016 +1200

    line 1
    line 2
    line 3

diff --git a/test b/test
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/test
@@ -0,0 +1 @@
+1
~/tmp/git $ echo 2 >> test
~/tmp/git $ git add test
~/tmp/git $ git commit -m 'line 1
> line 2
> line 3'
[master 7745993] line 1 line 2 line 3
 1 file changed, 1 insertion(+)
~/tmp/git $ git show
commit 77459934ddbcd9a557b5ee13bf2d72c43b4829fc
Author: pp <pp@pp.pp>
Date:   Mon Jul 4 19:29:56 2016 +1200

    line 1
    line 2
    line 3

diff --git a/test b/test
index d00491f..1191247 100644
--- a/test
+++ b/test
@@ -1 +1,2 @@
 1
+2