To install manually, simply import the CodeIgniterValetDriver.php file into your ~/.config/valet/Drivers folders. And believe it or not, You are good to go!
If you are too lazy, let your terminal do the work for you. Run the following command in your terminal.
cd ~/.config/valet/Drivers && { curl -O https://raw.githubusercontent.com/veekthoven/codeigniter-valet-driver/master/CodeIgniterValetDriver.php ; cd - ; }This driver assumes you have have not changed the location or name of your system folder.
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Enjoy!!