Create file without replacing variables:

cat <<'EOF' > /path/file
============================
My name is ${0}
I was input via user data
============================
EOF

If you check /path/file you will see exactly the content above. Create file REPLACING the variables while creating:

cat <<EOF > /path/file
============================
My name is ${0}
I was input via user data
============================
EOF

In this example, the variable ${0} will be replaced during the creation of the file, hence the content will display your username.