I found this by Googling "Irish blessings" and the words are similar but not the same.  They may have changed some of the lines of verse for the movie.

An Old Irish Blessing
May the road rise up to meet you.
May the wind always be at your back.
May the sun shine warm upon your face,
and rains fall soft upon your fields.
And until we meet again,
May God hold you in the palm of His hand.

http://islandireland.com/Pages/folk/sets/bless.html


On Ask.com, I found that someone had already asked where the verse in Blow had originated, and the most popular answer was this, which is the longer version of what I posted up above:


May the road rise to meet you,
May the wind be always at your back.
May the sun shine warm upon your face,
The rains fall soft upon your fields.
And until we meet again,
May God hold you in the palm of his hand.

May God be with you and bless you:
May you see your children's children.
May you be poor in misfortune,
Rich in blessings.
May you know nothing but happiness
From this day forward.

May the road rise up to meet you
May the wind be always at your back
May the warm rays of sun fall upon your home
And may the hand of a friend always be near.

May green be the grass you walk on,
May blue be the skies above you,
May pure be the joys that surround you,
May true be the hearts that love you.