Perisesarma bidens isn't difficult to keep. You essentially need to create a terrarium similar to something you'd use for newts or terrapins. Ideally make a bank of sand and stones above the waterline, but a pile of lava rock or bogwood works pretty well. Water depth need only be 5 cm or so, enough for moistening their gills. Water needs to be slightly brackish (around SG 1.005), filtered, and warm (around 25 C).
Like most land crabs they are omnivores that feed principally on fallen fruit and decaying vegetation. Banana and other soft fruits are favourites, as are tinned peas, but algae wafers (like those used to feed plecs) make ideal staples. Augment with moderate amounts of meaty foods with shells or bones to provide essential calcium. Frozen krill and frozen lancefish would be ideal.
The main problems are territoriality and a certain tendency to escape. Provide ample hiding places (e.g., halved coconut shells with "mousehole" openings) so that a crab can hide away during a moult. Otherwise it is very likely to be taken apart by its companions. Make sure the tank has a hood with gaps too small for a crab to escape.
Cheers, Neale