How much does an airliner cabin elongate at altitude?
We can identify three effects that have an effect on cabin length:

Stretching due to the bulkhead pulling on the end of the fuselage;
Shortening due to the fuselage expanding in diameter (Poisson effect)
Shrinkage due to temperature

These are simple solid mechanics problems. Given an airplane with length $l$, diameter $d$, wall thickness $t$ made with a material with Young's modulus $E$ and Poisson ratio $\nu$ and linear expansion coefficient $\alpha$ pressurised to a pressure differential $p$, cooled to a temperature differential $\Delta T$....
$$\Delta L = \dfrac{d p L}{ 4 t E} - \dfrac{\nu d p L}{2 t E} - \alpha \Delta T l$$
$$\Delta L = \dfrac{d p L(1-2\nu)}{ 4 t E} - \alpha \Delta T l$$
Let's have a wall thickness of 3mm, diameter of 4m, length of 40m subjected to 0.5bar and 70°C temperature difference. Aluminium $E=$70GPa, $\nu=0.33$, $\alpha=25\mu m/m°C$. Filling in the numbers, we obtain $$\Delta L=3.2mm-70mm\approx-67mm$$
So thermal expansion definitely has the upper hand here, shrinking the fuselage by a few centimetres in total, whereas pressurising the fuselage can only expand it by a few millimetres. The numbers here are very much approximate but the order of magnitude will not change much with &quot;real&quot; numbers.