This is a much-anthologized poem; Google Book Search has the complete text of 38 books that contain it. These lyrics were copied from The Complete Poetical Works of Thomas Campbell edited by J. Logie Robertson, 1907. I have boldfaced the differences between this text and the one posted by Sorcha above.

THE HARPER
Thomas Campbell, 1799

On the green banks of Shannon, when Sheelah was nigh,
No blithe Irish lad was so happy as I;
And no harp like my own could so cheerily play,
And wherever I went was my poor dog Tray.

When at last I was forced from my Sheelah to part,
She said (while the sorrow was big at her heart),
'Oh! remember your Sheelah when far, far away;
And be kind, my dear Pat, to our poor dog Tray.'

Poor dog! he was faithful and kind, to be sure,
And he constantly loved me, although I was poor;
When some sour-looking folk sent me heartless away,
I had always a friend in my poor dog Tray.

When the road was so dark and the night was so cold,
And Pat and his dog were grown weary and old,
How snugly we slept in my old coat of gray,
And he licked me for kindness—my poor dog Tray.

Though my wallet was scant I remembered his case,
Nor refused my last crust to his pitiful face;
But he died at my feet on a cold winter day,
And I played a sad lament for my poor dog Tray.

Where now shall I go, forsaken and blind?
Can I find one to guide me so faithful and kind?
To my dear native village, so far, far away,
I can never return with my poor dog Tray.

---

Click to play (The Harper-My Poor Dog Tray)