If it’s a pipe, then it’s the same as for a regular file. POSIX says[1] “the standard input and standard output streams are fully buffered if and only if the st

If it’s a pipe, then it’s the same as for a regular file. POSIX says[1] “the standard input and standard output streams are fully buffered if and only if the stream can be determined not to refer to an interactive device”; the Glibc implementation[2] looks at isatty(). [1] https://man7.org/linux/man-pages/man3/stdin.3p.html https://man7.org/linux/man-pages/man3/stdin.3p.html [2] https://sourceware.org/git/?p=glibc.git;a=blob;f=libio/filedoalloc.c;hb=HEAD https://sourceware.org/git/?p=glibc.git;a=blob;f=libio/filed...