Cat Text to File - EOL - Without opening text editor

To Create a NEW FILE:

Note: Without quotes around EOL it will expand variables vs put them in script!.

cat << 'EOL' >/tmp/filename
echo "this will be the first and only line in /tmp/filename"
EOL

var="this will be the first and only line in /tmp/filename"
cat << EOL >/tmp/filename
echo $VAR
EOL

To Append:

Same thing, but << EOL >> or << 'EOL' >>