Check if destination already exists

[sebastianv1]

Sample error if a binary is already linked to the destination, but was not installed by brew:

Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local
Could not symlink bin/<formula>
Target /usr/local/bin/<formula>
already exists. You may want to remove it:
  rm '/usr/local/bin/<formula>'

To force the link and overwrite all conflicting files:
  brew link --overwrite <formula>@0.1.5

To list all files that would be deleted:
  brew link --overwrite --dry-run <formula>@0.1.5

Possible conflicting files are:
/usr/local/bin/<formula>