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Re: read fails on null-byte: v4.1.7 FreeBSD 8.0 (amd64)


From: Matthew Story
Subject: Re: read fails on null-byte: v4.1.7 FreeBSD 8.0 (amd64)
Date: Wed, 23 Nov 2011 18:54:01 -0500

On Nov 23, 2011, at 4:47 PM, Chet Ramey wrote:

> On 11/23/11 9:03 AM, Matthew Story wrote:
>> Bash Version: GNU bash, version 4.1.7(1)-release (amd64-portbld-freebsd8.0)
>>          OS: FreeBSD 8.0
>>    Hardware: amd64
>> Environment: jail
>> Description: read terminates reading all records at first null-byte ( chr(0) 
>> ) in a stream, null-bytes are valid ascii characters and should not cause 
>> read to stop reading
>>              a line this behavior is not reproducible using bourne shell.
> 
> Bash doesn't stop reading at the NUL; it reads it and the rest of the line
> up to a newline.  Since bash treats the line read as a C string, the NUL
> terminates the value assigned to `foo'.  

it seems to terminate all assignment of the current line at the first `\0', not 
merely the value assigned to `foo':

[bash ~]$ printf '%s\0 %s\n%s\n' foo bar baz | while read foo bar; do echo 
"$foo" "$bar"; done | od -a
0000000    f   o   o  sp  nl   b   a   z  sp  nl                        
0000012

it's clear from this example (and from what you've said above) that read does 
not halt entirely here as it processes the next line correctly, and ` bar' is 
not left in the buffer after first read.  What I find confusing about this 
comment and Greg's comment (copied in below) ...

> [Greg Wooledge <address@hidden>]
> What happens here is bash reads until the newline, but only the "foo"
> part is visible in the variable, because the NUL effective ends the
> string.  

... is that if the line were fully assigned along the lines of my understanding 
of read, foo should be `foo', up to the null-bye which effectively terminates 
the string, and then bar should be `bar'.



> Bash doesn't drop NULs like the
> FreeBSD (not the Bourne) shell.

FreeBSD sh indeed, apologies for the misstatement.

> 
> Chet
> -- 
> ``The lyf so short, the craft so long to lerne.'' - Chaucer
>                ``Ars longa, vita brevis'' - Hippocrates
> Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/
> 



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