Homebrew: Could not symlink, /usr/local/share/man/man7 is not writable

Just follow these 4 steps

1. sudo chown -R $(whoami) $(brew --prefix)/*
2. brew doctor
3. brew prune
4. brew link cmake

The proposition of Mark Setchell to use sudo chown -R $(whoami):admin /usr/local/share/man is right. According to the Homebrew troubleshooting page:

If commands fail with permissions errors, check the permissions of /usr/local’s subdirectories. If you’re unsure what to do, you can run cd /usr/local && sudo chown -R $(whoami) bin etc include lib sbin share var Frameworks

but the proposition of Nano to use sudo is not a good one. According to the Homebrew FAQ:

Homebrew is designed to work without using sudo. You can decide to use it but we strongly recommend not to do so. If you have used sudo and run into a bug then this is likely to be the cause. Please don’t file a bug report unless you can reproduce it after reinstalling Homebrew from scratch without using sudo.