A couple facts: 1. POSIX requires a single whole line to be read (as Roberto pointed out already). 2. POSIX doesn't define what "affirmative" response is. GNU Coreutils reads the first char and discards the rest [0]. Busybox skips blanks, then takes a char as answer and discards the rest [1]. Both of these are "valid" according to POSIX.
[0]: https://github.com/coreutils/gnulib/blob/71288b12a5eb299e173a17245f548d5e2adb85c0/lib/yesno.c#L54-L59 [1]: https://github.com/mirror/busybox/blob/371fe9f71d445d18be28c82a2a6d82115c8af19d/libbb/ask_confirmation.c#L11-L27 Now to Roberto's proposal: while (isspace(ch = getchar())) ; This is wrong because isspace() will return true on newlines, thus it'll end up reading *multiple* lines. We must read only one. You want isblank() instead. Other than that: 1) Skipping leading blanks seems okay to me. 2) Rejecting any non-space trailing char is valid by POSIX but will also lead to some surprising results, such as "yes" being rejected. 3) IMO busybox's approach seems like a good behavior: skip leading blanks, ignore trailing chars. - NRK
