libutil:

	Functions:
		validatemode(const char *mode)
		validaterange(const char *range)
		getrange(const char *range, const char **offset)
			- Used for utilities such as cut -f fields
		concat()
			- Concatenate one file to another.
		uconcat()
			- Unbuffered version of concat().
		sponge()
			- Load a file into virtual address space and spill over into temp file if larger than threshold.
			- Maybe but sponge utility shouldn't use.
		dump()
			- Read from a file and dump to another.
			- Use O_NONBLOCK when possible for reading and writing.
			- Continue reading input file until EOF even if write end closed.