How can I install .pkg with a shell on macOS?

Just in case it's needed; if you want to installer a .pkg without root access:

installer -pkg myapp.pkg -target CurrentUserHomeDirectory 

will install the package in ~/Applications.

Install all .pkg files from the current folder to /Applications (or whatever target folder is configured in the package):

for f in *.pkg; do sudo installer -verbose -pkg "$f" -target / done 

As an alternative you can install the packages to your home folder with -target ~. They will end up in /Users/<your_account>/Applications unless a specific path is predefined in the installer.

^{If you want to see which specific folders a pkg installer writes to and which post-install scripts will be run then check out SuspiciousPackage (freeware, can be installed with brew install --cask suspicious-package), and use quick preview from Finder when a .pkg file is selected. Pressing spacebar in Finder with the selected file should work too. A similar shareware (nagware) app — Pacifist, can be used for inspecting and unpacking dmg/pkg and other container formats.}

Handling files with spaces and special characters

While the for f in *.xyz syntax looks 'clean' and neat, it is considered bad practice in bash because it is likely to fail on file names with spaces, quotes and other special chars. A more foolproof approach is to use find, e.g.

sudo -i find . -iname "*.pkg" -maxdepth 1 -exec installer -verbose -pkg {} -target / \; 

^{Note:-maxdepth 1 forces find to only search for files in the current folder and avoid traversing nested subfolders.}