diff --git a/README.md b/README.md
index 063e246..61d0b30 100644
--- a/README.md
+++ b/README.md
@@ -27,7 +27,6 @@ Below replace "marvin" with your 42 Network login.
 
 ```
 export USER="marvin"
-export MAIL="marvin@student.42lausanne.ch"
 
 ./set_header.sh
 ```
@@ -73,14 +72,15 @@ vim ~/.bashrc
 export USER="marvin"
 export MAIL="marvin@student.42lausanne.ch"
 <ESC> :wq
-. ~/.bashrc
+source ~/.bashrc
 ```
 
 ### **Note**
 
 - Your git username and email will always have the priority over $USER and $MAIL variables.
-- if you are outside a git repo tree, it will use the $USER and $MAIL environement variables.
-- if none of the above, it will default to marvin@student.42lausanne.ch and marvin as username.
+- If you are outside a git repo tree, it will use the $USER and $MAIL environement variables.
+- I none of the above, it will default to marvin@student.42lausanne.ch and marvin as username.
+- Usually you don't want to overwrite $USER as is the logged user and is already defined.
 
 Troubleshooting:
 ```
diff --git a/set_header.sh b/set_header.sh
index 2df8cb7..7312ccb 100755
--- a/set_header.sh
+++ b/set_header.sh
@@ -3,14 +3,27 @@
 
 # Set variables
 
-if [ ! -z "$USER" ]
+if [ -f "~/.zshrc" ]
 then
-    echo 'export USER=`whoami`' >> ~/.zshrc
+	if ! grep -q ' USER=' "~/.zshrc" ] && [ -z "$USER" ]
+	then
+		echo 'export USER=`whoami`' >> ~/.zshrc
+	fi
+	if ! grep -q ' MAIL=' "~/.zshrc" ]
+	then
+		echo 'export MAIL="${USER}@student.42lausanne.ch"' >> ~/.zshrc
+	fi
 fi
-
-if [ ! -z "$MAIL" ]
+if [ -f "~/.bashrc" ]
 then
-    echo 'export MAIL="${USER}@student.42lausanne.ch"' >> ~/.zshrc
+	if ! grep -q ' USER=' "~/.bashrc" ] && [ -z "$USER" ]
+	then
+		echo 'export USER=`whoami`' >> ~/.bashrc
+	fi
+	if ! grep -q ' MAIL=' "~/.bashrc" ]
+	then
+		echo 'export MAIL="${USER}@student.42lausanne.ch"' >> ~/.bashrc
+	fi
 fi
 
 test -d ~/.vim/plugin || mkdir -p ~/.vim/plugin