shell – How to Find Broken Symlinks

You could make a tar archive containing the symbolic links only. Assuming GNU utilities (so non-embedded Linux or Cygwin):

cd /some/dir
tar cf symlinks.tar --no-recursion .
find -type l -print0 | xargs -0 tar rf symlinks.tar

Another approach is to generate a shell script that would recreate the symlinks. Here's a Perl approach (while this is doable with only POSIX utilities, it's difficult to handle special characters correctly).

use File::Find;
sub wanted {
    if (-L $_) {
        $link_name = $_;
        $target = readlink($_);
        die $! if !defined $target;
        # protect single quotes from shell expansion
        $link_name =~ s/\x27/\x27\\\x27\x27/;
        $target =~ s/\x27/\x27\\\x27\x27/;
        print "ln -s -- \x27$target\x27 \x27$link_name\x27\n";
    }
}
find({wanted => \&wanted, no_chdir => 1}, ".")

Don't remove the symbolic links. Exclude them from the copy, or make a symlink-less copy of the directory tree, as illustrated in my answer to your other question.

What you're asking for doesn't make much sense in the general case, so it's not surprising that find has no provision for it.

A symlink with a relative target is relative to the path of the symlink. So for instance, if by traversing a directory by following symlinks, find encounters a/b/c/d and a, a/b, a/b/c are all relative or absolute symlinks (or symlinks to paths with symlink components), what should it do?

If you're looking for a find predicate or a GNU -printf % directive that expands to a symlink-free path to the file relative to the current directory or any directory, I'm afraid there's none.

If you're on Linux, you can get the absolute path of those files with:

find -L foo -type f -exec readlink -f {} \;

As you found out, there exists at least one realpath command which accepts more than one path argument which in combination with the standard -exec cmd {} + syntax is going to be a lot more efficient since it's running as few realpath commands as necessary:

find -L foo -type f -exec realpath {} +

find -L foo -type f -print0 | xargs -r0 realpath

might be quicker as if more than one realpath command is needed, find can keep on looking for more files while the first realpath starts working which even on a single processor system might make it more efficient.

-print0 and xargs -r0 are not standard, come from GNU but are found in a number of other implementations like most modern BSDs.

Zsh has builtin support for it:

print -rl foo/***/*(-.:A)

If you don't care about the sorting order, you can disable sorting and make it a bit more efficient with:

print -rl foo/***/*(-.oN:A)

If you want to convert those to relative paths to the current directory, you could have a look at that SO question.

If you know that all those files have an absolute canonical path (whose none of the components are symlinks) inside the current directory, you can simplify it to (still with zsh):

files=(foo/***/*(-.:A))
print -rl -- ${files#$PWD/}

Though short and convenient, and works whatever character filenames contain, I doubt it would faster than find + realpath.

With the Debian realpath and GNU tools, you can do:

cd -P .
find -L foo -type f -exec realpath -z {} + | 
  gawk -v p="$PWD" -v l="${#PWD}" -v RS='\0' -vORS='\0' '
    substr($0, 1, l+1) == p "/" {$0 = substr($0, l+2)}; 1' |
  xargs -r0 whatever you want to do with them

As I realise now, there's now a realpath in recent versions of GNU coreutils, which has the exact feature you're looking for, so it's just a matter of

find -L foo -type f -print0 |
  xargs -r0 realpath -z --relative-base . |
  xargs -r0 whatever you want to do with them

(use --relative-to . instead of --relative-base . if you want relative paths even for files whose symlink free path doesn't reside below the current working directory).