In these lines this is nearly always just a vowel being drawn out for effect rather than a piece of grammar: a raspberry sound effect, a whoa, an again, and a trailing-off explanation stretched at the end. Two more lines are false matches where the syllable belongs to another word entirely. Only one line, the order to shut your mouth, shows a real ending, a northern-style command form. The examples do not pin down a single meaning, so this entry stays open.
Register: sound effects and drawn-out speech
The examples below did not fully pin this one down — read them before relying on the entry above.