What is the exact function of the 'export' bulliten?

Question

According to the BASH Reference Manual:

export

export [-fn] [-p] [name[=value]]

    Mark each name to be passed to child processes in the environment.

An example I've come across:

PS1=<\u\h \W>\$

export PS1

What I've gleaned from the documentation, and examples, is that export is used to permeate a change in the environment across multiple shells? My confusion comes form the numerous times I have not seen it used in similar circumstances, yet everything remains working as intended.

E.g, I created an environment variable to track the load order of my profile files. Here is an example from my .bashrc file:

PROFILE_ORDER="$PROFILE_ORDER:~/.bashrc"

and it produces this behavior

$ echo $PROFILE_ORDER
/etc/bash.bashrc:~/.bashrc

If my understanding of export is correct, then why didn't I need to use it in creating and modifying $PROFILE_ORDER?

Answer 1

export is used to set variable which is accessible from a shell executed from your current shell.

> x=1
> export y=2
> echo $x $y
1 2
> bash
> echo $x $y
2

.bashrc is executed every time when you open new shell, so if I set y=2 there, it would be known in every new shell without using export