It's a low-lying plant with long skinny leaves colored green on the top and the underside is eggplant color. Is it a type of yucca?
I don't think it's a yucca. The article at this link shows a couple pictures of yucca: https://www.gardeningknowhow.com/ornamental/foliage/yucca/propagation-of-yucca-plant.htm
One image in particular should be helpful to you. It's at the bottom, right hand side after "read related articles".
If you could provide more information about the plant in question, it still could be identified. Height, width, length of leaf, sun, shade, bloom If any, ect.