On Debian-based systems and derivatives, use readlink.
Some useful options from the man page:
-f,--canonicalize
canonicalize by following every symlink in every component of the given name recursively; all but the last component must exist
-e,--canonicalize-existing
canonicalize by following every symlink in every component of the given name recursively, all components must exist
-m,--canonicalize-missing
canonicalize by following every symlink in every component of the given name recursively, without requirements on components existence
Note that this follows symlinks, so it’s not suitable for every use.