On Fri, 15 Jun 2018 15:15:23 +0200, Davide Brini <dave...@gmx.com> wrote:
> So it looks like the only "reliable" way to detect NULs in the input is to
> read one character at a time.
Your explanation got me thinking, and I've come up with the following code
that seems to be slightly more efficient than reading one byte at a time,
as it allows reading bigger chunks of data in the parts where there are no
delimiters (NULs). I'm posting it in case it helps someone. Works For Me
(TM).
----------------------------------
to_read=512 # how many bytes to read at a time
while true; do
IFS= read -d '' -r -n $to_read data
status=$?
length=${#data}
# do whatever with what we got
for ((i=0; i < length; i++)); do
printf "Read character %02x\n" "'${data:i:1}"
done
# if we read less than we wanted, and it's not EOF, it means we also have
# a delimiter
if [ $length -lt $to_read ] && [ $status -eq 0 ]; then
printf "Read a NUL\n"
fi
# exit if EOF
if [ $status -ne 0 ]; then
break
fi
done
----------------------------------
Tests:
$ printf '\x00' | ./test.sh
Read a NUL
$ printf '\x00\x00' | ./test.sh
Read a NUL
Read a NUL
$ printf '\x00a\x00' | ./test.sh
Read a NUL
Read character 61
Read a NUL
$ printf '' | ./test.sh
$ printf 'abcd' | ./test.sh
Read character 61
Read character 62
Read character 63
Read character 64
$ printf '\x001\x00\n' | ./test.sh
Read a NUL
Read character 31
Read a NUL
Read character 0a
--
D.
