How Does Pwd Operate?
gclv.es
gclv.es
Since there is so much history I often find it hard to see why things work the way they do, just by looking at how they work.
If one is ready to "cheat" on the question and look at a ready made answer this one is quite good: https://unix.stackexchange.com/questions/413204/how-does-uni...
I would summarise the reasons behind common UNIX shell implementation(s) of this as "directory names are not stable over the lifetime of a process" and "$PWD cannot be trusted".
This type of simple, clever design is what’s prompted me to pick up “the unix programming environment”, though I’m sure most of what it talks about it outdated. It’s been a fun read so far!