It's a good solution, but I can think of two limitations.

• That will work for symbolic links (on most devices), but not for hard links (other than "." and "..").

  $ echo foo > a
  
  $ ln a b
  
  $ cat b
  foo
  
  $ perl -MCwd=abs_path -E'say abs_path($_) for @ARGV' a b
  /tmp/a
  /tmp/b
  [download]

  You might be able to check stat's device plus inode fields to address this limitation on some devices on some systems.

• It also won't necessarily work across devices (since you could access the same file via two devices). The following all refer to the same file:

  C:\Temp\file
  \\?\C:\Temp\file          # Via UNC path
  \\localhost\C$\Temp\file  # Via localhost
  \\tribble\C$\Temp\file    # Via domain name
  \\10.0.0.6\C$\Temp\file   # Via IP address
  \\localhost\share\file    # Via share
  Z:\file                   # Given subst Z: C:\Temp
  [download]

  In general, this isn't solvable.