Bug 12566

Summary:	ash: read with -t 0 does not return failure if nothing is read after a successful first read
Product:	Busybox	Reporter:	Geoff Winkless <busybox>
Component:	Other	Assignee:	unassigned
Status:	RESOLVED INVALID
Severity:	trivial	CC:	busybox-cvs
Priority:	P5
Version:	1.31.x
Target Milestone:	---
Hardware:	All
OS:	Linux
Host:		Target:
Build:

Description Geoff Winkless 2020-02-19 17:58:10 UTC

echo "a" | if read -t 0 a ; then echo $a; a=cleared; if read -t 0 a; then echo $a; fi; fi

outputs

blah
cleared

I'm a little confused by this. Would expect the second read to return failure, but it does not. Indeed, any subsequent reads on the same pipe return true.

Can work around by using -t 0.001 but it seems a little odd.

Comment 1 Geoff Winkless 2020-02-19 18:02:25 UTC

And immediately after I hit "send" I realised that the first read is also not populating $a either - my initial tests were with "blah", I hadn't realised that it hadn't changed to "a" as expected.

So read -t 0 a simply doesn't populate a at all, but returns true.

Comment 2 Geoff Winkless 2020-02-19 18:16:52 UTC

This actually matches other shells' behaviour, even though unexpected on my part. Apologies for timewasting.