Fish is “a smart and user-friendly command line shell for Linux, macOS, and the rest of the family.”

set

scoping

-f --function    # function-scoped
-l --local       # block-scoped (or function-scoped)
-g --global      # current shell session
-U --universal   # persistent, available immediately to all fish sessions

exporting

-u --unexport    # do not export to child processes
-x --export      # export to child processes

lists

-a --append      # append to list
-p --prepend     # prepend to list