How do I determine whether a symlink is dangling (broken)?

The documentation on this is fuzzy, but it turns out you can do this with shell builtins:

# Bash
if [[ ( -L $name ) && ( ! -e $name ) ]]
then echo "$name is a dangling symlink"
fi

The Bash man page tells you that "-L" returns "True if file exists and is a symbolic link", and "-e" returns "True if file exists". What might not be clear is that "-L" considers "file" to be the link itself. To "-e", however, "file" is the target of the symlink (whatever the link is pointing to). That's why you need both tests to see if a symlink is dangling; "-L" checks the link itself, and "-e" checks whatever the link is pointing to.

POSIX has these same tests, with similar semantics, so if for some reason you can't use the (preferred) [[ command, the same test can be done using the older [ command:

# POSIX
if [ -L "$name" ] && [ ! -e "$name" ]
then echo "$name is a dangling symlink"
fi