bin/177674: /bin/sh 'while read X' loop problem

[Joe Public]

>Number:         177674
>Category:       bin
>Synopsis:       /bin/sh 'while read X' loop problem
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sat Apr 06 20:40:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     Joe Public
>Release:        FreeBSD 9.1-RELEASE i386
>Organization:
none
>Environment:
System: FreeBSD 9.1-RELEASE FreeBSD 9.1-RELEASE #0 r243826: Tue Dec 4 06:55:39 UTC 2012 root at obrian.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC i386
>Description:
There is some kind of problem with 'read' in a sh(1) loop,
but it is only demonstrated with some programs (such as mplayer).
>How-To-Repeat:
First, create a file with some valid MP3 pathanmes inside, then:

OK:   while read X; do echo    $X; done < FILEWITHMP3PATHNAMES
OK:   while read X; do ls -l   $X; done < FILEWITHMP3PATHNAMES
FAIL: while read X; do mplayer $X; done < FILEWITHMP3PATHNAMES

This last command line will fail in a mess of corruption,
and it is difficult to explain what is actually occurring.
With only 1 pathname in the file, it works OK, but with 2
or more, it increasingly results in more and more corruption.
>Fix:
I don't know what the problem is.  I tried inserting sleep(1)
commands to make the loop slow and other things, but nothing
made any difference.
>Release-Note:
>Audit-Trail:
>Unformatted: