With Homebrew, how to check if a software/package is installed?

Question

I'm installing a set of softwares/packages/formulas via homebrew with command like

brew install <formula1>
...
brew cask install <formula2>
...

I wonder if it's a good idea to verify if the softwares <formula1>, ..., <formula2>, ... are already installed and only trigger the above commands for the ones NOT already installed. If so, how?

Answer 1

you could do something like this:

brew list <formula1> || brew install <formula1>

This will error on list and continue with install if not installed otherwise it will just list package files. (one could modify this further as a function or alias in .bashrc to make it easier to type)

Answer 2

It should also be noted that you can type brew info <formula> which will tell you whether or not a formula is installed. You can parse the response for "Not installed" and then run the installer if it finds the string.