sass --help OR sass -h OR sass -? will give you a whole list of commands you can use and how to use them.

sass --style compressed main.css will output a compressed version of main.css in the console.

sass --style compressed main.css:main.css the file before the : is the input file and the one after is the output file.

sass --style expanded main.css:main.css converts to ‘expanded’ style, which is nested but without the indentation.

sass -l main.css:main.css -l flag adds line numbers (as well as file name) corresponding to where the code is in the .sass file and adds it as comments to the .css output.

@mixin old {
    @warn "Please use new() instead"
}

@warn let’s you warn users about the code. For example, if a mixin/code/function is deprecated, you can warn the users about it and tell them to use the new one. @warn is added in the .scss file and is outputted in the console. In other words, it prints an error to Terminal showing a defined message.

Notes:

  • When an error is at the end of a line, it is usually a missed semi colon ;