Dash: double the distance you can walk
this turn.
Disengage: your movement
this turn does not provoke AoAs.
Dodge: if you are attacked at any time
from now until the start of your next turn that attack roll has disadvantage.
Attack: you may execute the attacks that you have
from now until the end of this turn.
Hide: you become hidden
until your Stealth check is beaten, your cover goes away, or you do something to end your hidden condition.
There are two ways to view when an action ends:-
1) 'taking an action' is an instantaneous event, but the
effects of that action (movement, not provoking, dodging, executing your attacks, being hidden) have a duration.
2) 'taking an action' is the same thing as the action itself, which means the action itself has a duration, and the action has not ended until that duration expires. Dash, Disengage, Attack start when you 'take the action' and only end when your turn ends. Dodge starts when you take the action and only ends at the start of your next turn. Hide starts when you take the Hide action and only ends when you are discovered, your cover goes away, or if you do something to end it.
If 1) is true, then yes, 'actions are indivisible', but not because there is any such rule but because 'taking an action' is an instantaneous event and you cannot divide 'instantaneous'. However, the
effects of that action have a duration, and nothing prevents those effects being divided. This means that your bonus action shove has been generated as soon as you 'took the attack action' and you are now free to use that bonus action whenever you want, even between attacks or before you execute your first attack.
If 2) is true, then the question of whether or not 'actions are indivisible' becomes relevant.
2a) Actions ARE divisible: this means you can cast a bonus action spell
while you are in the middle of an action. So you can
misty step after you take the Dash action, the Disengage action, the Dodge action,
the Attack action, the Hide action, etc. This means that you definitely can take the bonus action shield bash between attacks, and arguably before you execute the first attack.
2b) Actions are NOT divisible: this means that you
cannot cast a bonus action spell while you are in the middle of an action. So you could not
misty step after you take the Dash action! The Disengage action! The Dodge action! The Attack action! OR the Hide action!
It also means that a rogue who uses Cunning Action to Dash or Disengage as a bonus action before he uses his action for anything, now
cannot take his actual action for anything at all!
Actions are indivisible, so because his Dash or Disengage started when he took that bonus action and will not end until the end of his turn, his turn is already over before he can use his action for anything!
Also, since some posters are fond of asserting that you can only move between attacks is because there is a clause which says you can, and without such a clause then you could not, this means that you cannot move
during any action
except the Attack action! If 2b) is true AND that assertion is true, then after you take the Dash, Disengage or Dodge actions,
you are not allowed to move!
I contend that 2b) is absurd. There is no reason at all to suppose that you cannot take a bonus action after you Dash, Disengage, Hide or Dodge, and there is no excuse for treating the Attack action differently without a written rule which says so; if you do, that is the fallacy of Special Pleading.
It is also absurd to imagine you cannot move after you take the Dash or Disengage actions! They would become meaningless! This shows that the clause which says you can move between attacks is not a rules exception, it just reminds us that the ability to divide your move is not restricted by multiple attacks, important for players of previous editions who would assume the opposite.
If 2b) is absurd, this leaves either 2a), which certainly allows a bonus action between attacks and arguably allows it before the first attack, and 1) which certainly allows the bonus action between attacks or before your first attack.
Easy!
