I have a csh script (although I can change languages if it has any relevance) where I have to:
sed s/AAA/BBB/ file
The problem is that AAA
sed can use any separator instead of / in the s command. Just use something that is not encountered in your paths:
s+AAA+BBB+
and so on.
Alternatively (and if you don't want to guess), you can pre-process your path with sed to escape the slashes:
pwdesc=$(echo $PWD | sed 's_/_\\/_g')
and then do what you need with $pwdesc.