Green’s Dictionary of Slang

grub v.²

(UK Und.) to walk (unsteadily).

1833

‘The Beak and Trap to Roost are Gone’ in Swell!!! or, Slap-Up Chaunter 48: Lush’d heavy coves with queerish stamps, / Grub on their reeling way.

In derivatives

grubbed (adj.)

exhausted, unsteady.

1914

C. Holme Lonely Plough (1931) 121: I can’t help feeling a bit grubbed, but I suppose I can stick it out.

In phrases

grub along (v.)

to subsist, to struggle along.

1888		Daily Tel. 19 Oct. n.p.: When a youth left school to follow the pursuits of life he found that he had to grub along as best he could [F&H].
1925		S. Lewis Arrowsmith 341: Oh – no – gee – I’m just grubbing along, I guess.
1936		N. Marsh Death in Ecstasy 74: Here we go grubbing along – however.