envsubst: command not found on Mac OS X 10.8

Edit: @cobberboy 's anwer is more correct. upvote him.

brew install gettext
brew link --force gettext 

Following is my old answer:

envsubst is included in gettext package.

Therefore you may compile it by your own, using standard build tools such as make or using homebrew.

However, it seems to have little issue when installing gettext in MacOS. See following url for details: How to install gettext on MacOS X

brew install gettext
brew link --force gettext 

This will enable envsubst on OS X, and force it to link properly. It requires homebrew to be installed.