POSIX Issue 7, XCU, sh, STDIN says: When the shell is using standard input and it invokes a command that also uses standard input, the shell shall ensure that the standard input file pointer points directly after the command it has read when the command begins execution. It shall not read ahead in such a manner that any characters intended to be read by the invoked command are consumed by the shell (whether interpreted by the shell or not) or that characters that are not read by the invoked command are not seen by the shell. I.e. sh <<EOF id cat good! EOF must execute id, then execute cat, then the cat must copy "good!" to the standard output stream, and similarly sh <<"EOF" id read Q good! echo Q$Q EOF must execute id, then read "good!" into Q, then echo "Qgood!". Heretofor the output was as such: uid=1000(nabijaczleweli) gid=100(users) groups=100(users) ./dash: 3: good!: not found and as such (with -x): + id uid=1000(nabijaczleweli) gid=100(users) groups=100(users) + read Q + good! sh: 3: good!: not found + echo Q Q and a strace confirms: read(0, "id\ncat\ngood!\n", 8192) = 13 read(0, "id\nread Q\ngood!\necho Q$Q\n", 8192) = 25 Reading the standard input byte-by-byte is the obvious solution to this issue, Just Works, and is how all of shells do it on non-seekable input (we could, theoretically, read regular files block-wise, then seek within them after parsing, but the complexity out-weighs the rarity of running sh < program; we could also do whole-line reads on teletypes in icanon mode, but, again, the gain here is miniscule for an interactive session, and the mode can change at any time, so...). Naturally, we keep reading block-wise from not-standard-input. With this patch, we observe the correct uid=1000(nabijaczleweli) gid=100(users) groups=100(users) good! and + id uid=1000(nabijaczleweli) gid=100(users) groups=100(users) + read Q + echo Qgood! Qgood! Fixes: https://bugs.debian.org/862907 --- src/input.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/input.c b/src/input.c index ec075f5..6b6113e 100644 --- a/src/input.c +++ b/src/input.c @@ -195,7 +195,7 @@ retry: } else #endif - nr = read(parsefile->fd, buf, IBUFSIZ - 1); + nr = read(parsefile->fd, buf, parsefile->fd == 0 ? 1 : IBUFSIZ - 1); if (nr < 0) { -- 2.30.2
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