Buffering and Blocking


The stdio library offers three different buffering policies
_IOFBF: Full buffering (typically 4k o 16k)
_IOLBF: Line buffering (up to the newline character)
_IONBF: No buffering
For details, see setvbuf(3)

Buffering interferes with pipes (and sockets, and poll/select)
If stdin/out are not terminals, the default is _IOFBF
So the writing process may not be actually write(2)ing
The reading process can block waiting for data that doesn't arrive
Interactive use, with grep(1), can be disappointing
That's why many commands offer "-l" or force _IONBF

Example: using tee to replicate terminals