cat data
This is the header line.
This is the first data line.
This is the second data line.
This is the last line.
tac data
This is the last line.
This is the second data line.
This is the first data line.
This is the header line.
sed -n '{1!G;h;$p}' data
This is the last line.
This is the second data line.
This is the first data line.
This is the header line.