Completion for grubby command

One of the useful features of grubby is the ability to use tab completion
to easily find and specify the kernel version we want to do with it. This
saves time compared to manually checking the full path of different
kernel versions installed

completions/grubby

@@ -0,0 +1,45 @@
+# grubby(8) completion                                        -*- shell-script -*-
+
+_grubby() {
+	local cur prev commands
+	commands="--default-kernel --default-index --default-title --info --make-default --set-default --set-default-index --update-kernel --args --remove-args"
+
+	COMPREPLY=()
+	cur="${COMP_WORDS[COMP_CWORD]}"
+	prev="${COMP_WORDS[COMP_CWORD - 1]}"
+
+	case "${prev}" in
+	grubby)
+		COMPREPLY=($(compgen -W "${commands}" -- ${cur}))
+		return 0
+		;;
+	--info)
+		kernels=$(ls /boot/vmlinuz-*)
+		COMPREPLY=($(compgen -W "ALL DEFAULT $kernels" -- ${cur}))
+		return 0
+		;;
+	--set-default)
+		kernels=$(ls /boot/vmlinuz-*)
+		COMPREPLY=($(compgen -W "$kernels" -- ${cur}))
+		return 0
+		;;
+	--set-default-index)
+		numkernels=$(ls -t /boot/loader/entries/ | wc -l)
+		maxindex=$((numkernels - 1))
+		indexes=$(echo $(seq 0 $maxindex))
+		COMPREPLY=($(compgen -W "$indexes" -- ${cur}))
+		return 0
+		;;
+	--update-kernel)
+		kernels=$(ls /boot/vmlinuz-*)
+		COMPREPLY=($(compgen -W "$kernels" -- ${cur}))
+		return 0
+		;;
+	--args | --remove-args)
+		COMPREPLY=($(compgen -W "" -- ${cur}))
+		return 0
+		;;
+	*) ;;
+	esac
+}
+complete -F _grubby grubby