AW: Re: read command sometimes misses newline on timeout

[Thomas Oettli]

I agree with you, but it should never happen that read returns timeout, also 
returns the full line and has already read the newline character.
If that happens, there is no way for the script to decide what to do. Please 
see the provided test script, it showcases the error.

If I did a mistake there, I would gladly change it. But I currently don't see 
any way how to handle this properly from the script side.

Please also see the answer from Martin D Kealey, I think he is on to something:
https://lists.gnu.org/archive/html/bug-bash/2024-10/msg00007.html




On 10/4/24 8:18 AM, Thomas Oettli via Bug reports for the GNU Bourne Again
SHell wrote:

> Bash Version: 5.2
> Patch Level: 26
> Release Status: release
>
> Description:
> I have tried to write a bash script that asynchronously reads from a pipe 
> (line by line) with the help of "read -t".
> If the timeout occurs in just the right moment, read returns the full line, 
> but the return code says timeout (rc > 128).

If the read command times out, it always returns > 128, so if you have a
return code in that range, you can assume read timed out and react
accordingly.

> Therefor it is not possible to know if a full line was returned or not.

When read times out, it always returns what it read before the timeout in
the buffer, so you don't lose any data. Whether or not that's a `full line'
is up to timing, and it's up to the script to decide how to cope with it.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU chet@case.edu http://tiswww.cwru.edu/~chet/