How to fix a metal rail in a gap

I want to put a metal rail between two walls, there might be other bits too but basically a bar across the room fixed at either end.
I found people selling "tube clamp" products which I think is what I want, e.g: https://www.themetalstore.co.uk/key-clamp-fittings/tube-clamp-uk-suppliers



But say the span is 200cm and you have to recess each end in the wall plate... now your pipe is too long as you try to get it in. How do people do this? Similar issue to connecting soil pipes I suppose.
Even if you have a join in the middle you're still going to end up trying to force it, bending pipe that really doesn't want to bend.

Is there a trick to it that's obvious once you know?

When I've done similar, I always make the pipe about 5-10mm shorter than the gap, so you can fit it in.

The gap is covered by the end of the clamp and once the grubber screws are tight, it doesn't move about

The pipe doesn't need to be the size of the gap. You can see where the grub screw fits and so long as the end of the pipe reaches the hole (just past) you're ok.
You can get enough slop in the system to move it into position. Probably easier to drill the holes first and have a friend hold the rail while fixing it with one screw at each end.

Ok thanks guys. I don't have a feel for how much give this material has so it's helpful to hear your experiences.