The brew manager needs files in /usr/local/share to be writeable by the user who runs brew. In the case of my user, 'alan' in macosx, I changed the group ownership of all files under /usr/local/share to admin of which my user belongs to.

MacOSX is POSIX compliant which means that nothing is installed under /usr/local by default; /usr/local is brew's default PREFIX.

Key commands:
$brew update
$brew outdated
$brew upgrade
$brew upgrade

See what formulas are installed:
$brew list

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