There are multiple ways you could do this (it's just normal Linux stuff), for example:
Type in the beginning of the command and then press TAB. If there is only one command that starts with those characters it will auto-complete the command. If there are multiple commands that start the same way pressing TAB a
second time will list all the possibilities.
Code:
admin@RT-AC68U:/# mtd-
mtd-erase2 mtd-unlock mtd-write2
Alternatively you could just search the entire filesystem for a specific command.
Code:
admin@RT-AC68U:/# find / -name mtd-erase2
/sbin/mtd-erase2
And as you said, typing a command followed by "-?" usually gives the command syntax or an error if it doesn't exist.
Code:
admin@RT-AC68U:/# mtd-erase -?
-sh: mtd-erase: not found
admin@RT-AC68U:/# mtd-erase2 -?
usage: mtd-erase2 [device]