Linebuffered

Line buffering is a mode of buffered I/O in which data is accumulated in a temporary memory buffer and flushed to the underlying device when a newline character is output, or when the buffer becomes full, or when an explicit flush is requested. This contrasts with fully buffered I/O, which may flush only when the buffer fills, and unbuffered I/O, which writes each operation directly.

On output streams, line buffering is common for programs that interact with terminals. When stdout is connected to a terminal, many libraries implement line buffering so that each line becomes visible after a newline is written. If stdout is redirected to a file or pipe, the stream may switch to full buffering or another mode.

On input streams, line-oriented behavior means input is delivered to the program per line; the system often waits for a newline before providing the data to the program. This is related to terminal settings where canonical (line-oriented) input is used, in contrast to raw or non-canonical modes.

Implementation and controls vary by language and library. In C, line buffering is controlled via setvbuf with the _IOLBF option. In Python, buffering can be configured when opening a file or stream (for example, buffering=1 enables line buffering in some contexts). Other environments offer analogous controls for enabling or disabling line buffering.

Advantages of line buffering include lower latency for interactive programs and fewer system calls than unbuffered I/O. However, it can be less efficient for bulk data transfers due to frequent flushes, and the behavior can vary depending on whether the I/O target is a terminal or a file.

See also: buffering, fully buffered I/O, unbuffered I/O.