One version in the DT is here.

The version I have heard differs but little:

Jock MacGraw

Behold, I am a soldier bold,
and only twenty five years old,
a braver warrior never was seen,
frae Inverness tae Gretna Green.

When I was young, my father said,
he would put me tae a decent trade,
but I did na' like the job at a',
so I went and joined the Forty-Twa.

Chorus:
The wind may blaw, the cock may craw,
the rain may rain and the snaw may snaw,
But you wid'na frighten Jock MacGraw,
he's the stoutest man in the Forty-Twa

The sergeant, when he 'listed me,
he winked his e'e and then says he:
A man like you sae stout and tall,
Can ne'er be killed by a cannonball

The captain then, when he cam round,
he looked me up and looked me down,
Then turning to the sergeant, "Why you scamp,
you've 'listed the bleachfield, out 'n' tramp."

Chorus

At our last fecht, across the sea,
the general, he sends after me,
When I get there, and my big gun,
Of course, the battle, it was won.

The enemy all run awa',
they were feared at the likes o' Jock MacGraw,
A man like me, sae tall and neat,
Ye ken yoursel' he could never be beat.

Chorus

The King then held a grand review,
we numbered a thousand and sixty two,
The Kilty lads come marchin' past,
and Jock MacGraw come marchin' last.

The royal party grab their sticks,
and a' began to stretch their necks,
Crys the king to the colonel, "Upon my soul,
I took that man for a telegraph pole."

Chorus

From "25 Scottish Favorites" (Cassette)
Singer unknown

The most obscure part of this is the line about the bleachfield. A bleachfield is a field where linen was laid out to bleach in the sun, therefore the line simply alludes to a large object.