On 12/14/10 17:55, David Korn wrote:
cc: [email protected]
Subject: Re: [ast-users] ksh read byte
--------
The builtin manual of ksh's "read" says:
"-N nbyte Read exactly nsize characters.
For binary fields size will be in bytes."
I've tried to read single bytes with "read -N1". The following, using
"od", works as expected and thus confirms that "read -N1" is working:
#!/bin/ksh
exec 3< hexfile ## file of 256 bytes: 0, 1, 2, 3, ... 255
while read -u3 -r -N1 B
do
H=$(printf "$B" | od -tx1 -An)
print ${H:=" 00"}
done | less
exec 3<&-
But I want to compare $B to constant values, and print $B as ascii-hex,
and I'd like to avoid using external application "od". If I declare B
with "typeset -is", or "typeset -i", or "typeset -b", the result is
"arithmetic syntax error" or nonsense. Behavior is the same for locale
"C" and "en_ZA.utf8". Of course it can be done (ksh can do anything!)
but please tell me, "How?".
Assuming that the data you read in is a valid character in that locale,
I would expect that in the C locale
exec 3< hexfile ## file of 256 bytes: 1, 2, 3, ... 127
while read -u3 -r -N1 B
do print -r -- $(('$B'))
done | less
exec 3<&-
would work. However, for 0 or a character not in the current locale,
this will not work. read return the Empty string for the 0 byte.
You could use
printf "%d\n" "'$B'"
instead and shorten it to
while read -u3 -r -N1 B
do printf "%d\n" ${B+"'$B'"}
done< hexfile | less
which also handles 0.
read will return 1 for an invalid character.
David Korn
[email protected]
David -
Many thanks! With a couple of tweaks, I got what I wanted:
while read -r -N1 B
do
printf "%02X " ${B:+"'$B'"}
done < hexfile | less
That works for 0..255 on both locales "C" and "en_ZA.utf8". The ":"
before the "+" proved essential. Is operation for inputs 128-255 a
fluke which may change with ksh version?
Bob Barry
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