Greetings, while troubleshooting a test failure for pcre2[0] in OpenBSD, tracked down the problem to code that was inherited from NetBSD for their fseek implementation in libc.
it can be worked around by calling lseek directly or by removing the buffer, which would seem not to be updated if the seek is short enough to be done directly in the buffer. pcre2grep implements an -m flag that can be used to tell it a maximum number of matches, after which it will exit; but needs to keep a state of the last position of the stream that was processed, so that the process could be resumed. the following works in Windows/Linux/macOS : $ printf "1\n2\n3\n" > i && ( head -1; head -1; cat ) < i && rm -f i 1 2 3 but only works in recent NetBSD if STDBUF0=U is set (which is not available in OpenBSD or other derivatives that are also affected (ex: AIX)) is this a bug (it would seem to contradict ANSI C, and yes I tried `fflush(stdin)` and didn't help) but the only way I found in the code was to skip the optimization and call lseek, which obviously would be detrimental performance wise, and obviously code hasn't changed in decades. Carlo [0] https://github.com/PhilipHazel/pcre2/issues/10 [1] https://gist.github.com/carenas/7c13147ef10365bec2595c9e87102ae7
