En mi mac OSX Yosemite.
cuando hago un brew update
error: unable to unlink old 'bin/brew' (Permission denied)
error: unable to unlink old 'share/man/man1/brew.1' (Permission denied)
OK. Así que hago un sudo brew update
MacBook-Pro:bin$ sudo brew update
Password:
Error: Cowardly refusing to 'sudo brew update'
You can use brew with sudo, but only if the brew executable is owned by root.
However, this is both not recommended and completely unsupported so do so at
your own risk.
Por lo tanto, no me permite ejecutar la actualización de ninguna manera.