Sublime in 2023 only has "Save on Build" not "Build on Save" built in.. use: https://github.com/alexnj/SublimeOnSaveBuild

• Tools ➡️ Build System ➡️ New Build System...

{
	"shell_cmd": "python -u $file",
	"file_patterns": ["*.py"],
	"working_dir": "$file.path",
}

• "file_patterns": ["*.py"], will run build for this extension, OR...
• "selector": "source.python", will run build for this syntax.
• "file_regex": "" for formatting build output in console.
• Variables available: https://www.sublimetext.com/docs/build_systems.html#variables

CTRL+B... Choose using SHIFT+CTRL+B

All *.css files into main.css.

{
	"shell_cmd": "cd $folder; find . -type f -name \"*.css\" ! -name \"main.css\" -exec cat {} \\; > main.css",
	"file_patterns": ["*.css"],
}

...same but using your own script.

{
	"shell_cmd": "cd $folder; test -f doit.sh && ./doit.sh css",
	"file_patterns": ["*.css"],
}

• https://www.sublimetext.com/docs/build_systems.html