On 2011-07-20 14:34 +0100, Ralph Corderoy wrote: > No. Here's my understanding of how it currently works. The built-in > printf works out a character to print at a time; no foresight needed or > used. It asks the C library to print it with putchar(3). The C library > can implement buffering to avoid too many expensive write(2) system > calls. bash has the C library buffer stdout by lines. Each time > putchar(3) is called the character is appended to the buffer. If the > character was '\n' or the buffer is now full then write(2) is called to > pass the buffer to the kernel and the buffer then treated as empty. > > When printf is finished the buffer is flushed, e.g. if there's anything > in it then write(2) is called. > > The C library provides two other modes of buffering, see setvbuf(3). > bash could easily detect that stdout is a regular file, have a new > stream be duplicated from file descriptor 1, and set it to > block-buffered.
If standard output is a log file, log entries could remain latent for a very long time. The buffering mode we really want is buffered with a forced flush at reasonable intervals, E.G. one second after the last write. Unfortunately, there's no such thing in stdio. -- André Majorel http://www.teaser.fr/~amajorel/
