Detect if homebrew package is installed - bash

Question

I'm about to write a shell script to detect if several homebrew packages are installed in the system. Is there a way to use a brew command to achieve that?
I tried using the exit code of brew install <formula> --dry-run. But this builds the package if it is missing.

Answer 1

You can use
brew ls --versions myformula
to output the installed versions of the respective formula. If the formula is not installed, the output will be empty.
When using a recent versions of homebrew, which you can get with brew update, you can just run this (thanks Slaven):
if brew ls --versions myformula > /dev/null; then
# The package is installed
else
# The package is not installed
fi
That said, it is probably a good idea to check for the existence of the tool at all and not just checking for the respective homebrew package (e.g. by searching for the executable in the $PATH). People tend to install tools in a rather large amount of ways in practice, with homebrew being just one of them.

Answer 2

# install if we haven't installed any version
brew ls --versions $lib || brew install $lib
# install if we haven't installed latest version
brew outdated $lib || brew install $lib

Answer 3

What about?
for pkg in macvim ngrep other needed packages; do
if brew list -1 | grep -q "^${pkg}\$"; then
echo "Package '$pkg' is installed"
else
echo "Package '$pkg' is not installed"
fi
done

Answer 4

Easiest two-liners:
Step one, make sure it's installed
$ realpath . || brew install coreutils
This will print out the realpath of current dir, if not, then it will install it.
And it will not fail even realpath not found.
Step two, call it in your actual code:
$ realpath ${someDir}

Answer 5

For script and automation usage, I found out that brew bundle --help is very convenient.
If you do not want to use real bundle file, this snippet works fine in scripts:
brew bundle -v --file=- <<-EOF
brew "mc"
brew "ffmpeg"
brew "wget"
cask "cpuinfo"
cask "intel-power-gadget"
cask "unetbootin"
cask "vlc"
EOF
The good side of it, it will automatically detect if package is not installed, if it is outdated and only then will install it.
If you do not want updates, add a flag --no-upgrade. I have put -v for verbosity, as want more details, but you can skip it, or even use -q for even more silent run.