Find unused CSS classes in html,php,js files for multiple themes. Run this script in "themes" directory of Wordpress

find_unused_css_classes.sh

#!/bin/bash
for dir in $(ls -d */ | grep -v cache | grep -v node_modules | cut -f1 -d'/'); do
    (
        echo "checking $dir :";
        pushd "$dir" &>/dev/null || {
            printf "error: failed to change to %s\n" "$dir" >&2
            continue
        }
        echo "--------------------------------";
        cat $(find app/styles/ -type f) |
        grep -Eo '\.[a-z]+[a-z0-9_-]*' | sort | uniq | sed s/.// |
        
        while read CSS; do
        if ! grep -Erqi "([^(remove|has)]?class[(:|=|[:space:]*=>[:space:]*)]*[[:space:]\W]*[(\"|')]*[-a-z0-9[:space:]]*$CSS|\\.$CSS\b)" app/scripts/ assets/ campaigns/ components/; then
            echo $CSS >> unused.scss;
        fi
        done
        echo "--------------------------------";
    )
done

This is to scan multiple themes. You can use it for one theme only as well.

All you need to do is getting rid of for loop and $dir related lines.

And don't forget to update folder names to scan.

Tested on mac.