[ruby-on-rails] How to tell if homebrew is installed on Mac OS X

I am doing some Rails programming and I consistently see Homebrew referenced in solutions around the web but have never used it.

I also notice Homebrew in the terminal version 2.9 as an option next to "Shell -> New" from the terminal drop down but when I select homebrew and issue commands, they fail.

Usually with the "command not found" error.

Strangely enough I have been unable to locate a simple command to determine whether brew is installed or not.

How do I check to see if Homebrew is already installed on my Mac?

I use this to perform update or install:

which -s brew
if [[ $? != 0 ]] ; then
    # Install Homebrew
    ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
else
    brew update
fi

brew doctor checks if Homebrew is installed and working properly.

use either the which or type built-in tools.

i.e.: which brew or type brew

The standard way of figuring out if something is installed is to use which.

If Brew is installed.

>>> which brew
/usr/local/bin/brew

If Brew is not installed.

>>> which brew
brew not found

Note: The "not installed" message depends on your shell. zsh is shown above. bash will just not print anything. csh will say brew: Command not found. In the "installed" case, all shells will print the path.)

It works with all command line programs. Try which grep or which python. Since it tells you the program that you're running, it's helpful when debugging as well.

In my case Mac OS High Sierra 10.13.6

brew -v

OutPut-
Homebrew 2.2.2
Homebrew/homebrew-core (git revision 71aa; last commit 2020-01-07)
Homebrew/homebrew-cask (git revision 84f00; last commit 2020-01-07)

brew -v or brew --version does the trick!

[ ! -f "`which brew`" ] && echo "not installed"

Explaination: If brew is not installed run command after &&

Once you install Homebrew, type command brew doctor in terminal.

• If you get the following message:

  Your system is ready to brew

  then you are good to go and you have successfully installed homebrew.

• If you get any warnings, you can try fixing it.

Another one possible way:

# Check if Ninja is installed
if ! which ninja > /dev/null
then
echo 'Ninja installation...'
brew install ninja
fi

Running Catalina 10.15.4 I ran the permissions command below to get brew to install

sudo chown -R $(whoami):admin /usr/local/* && sudo chmod -R g+rwx /usr/local/*

While which is the most common way of checking if a program is installed, it will tell you a program is installed ONLY if it's in the $PATH. So if your program is installed, but the $PATH wasn't updated for whatever reason*, which will tell you the program isn't installed.

(*One example scenario is changing from Bash to Zshell and ~/.zshrc not having the old $PATH from ~/.bash_profile)

command -v foo is a better alternative to which foo. command -v brew will output nothing if Homebrew is not installed

command -v brew

Here's a sample script to check if Homebrew is installed, install it if it isn't, update if it is.

if [[ $(command -v brew) == "" ]]; then
    echo "Installing Hombrew"
    /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
else
    echo "Updating Homebrew"
    brew update
fi

I just type brew -v in terminal if you have it it will respond with the version number installed.