[cs631apue] `ls | more` hangs unless stderr is redirected

[kthompso]

I am having an issue trying to run the ls-test file against my ls 
implementation.
It keeps hanging and timing out at this command `./ls 
~jschauma/apue/ls-test | more`.

# ./ls-test
./ls ~jschauma/apue/ls-test | more
timed out

If I run the command directly from the terminal it acts as expected:

# ./ls ~jschauma/apue/ls-test | more
D
a
a.out
asdasd
b
big
c
file.hole
file.nohole
foo9bar
fooDbar
log
moo
symlink
thisisaratherlongfilenamemuchlongerthanmostoftheothers

The system ls also hangs when output to a pipe inside a shell script.

# ./ls-test
ls ~jschauma/apue/ls-test | more
timed out

But again -- from the terminal directly it works as expected.
The only way I can get it to not hang is to redirect stderr to a file.

# ./ls-test
ls | more
timed out

./ls | more
timed out

ls | more 2>/dev/null
ls
ls-test
ls.c
makefile
tmp

./ls | more 2>/dev/null
ls
ls-test
ls.c
makefile
tmp

And of course `ls-test 2>/dev/null` works as well.
This same approach doesn't work when redirecting stderr to stdout.

# ./ls-test
ls | more 2>&1
timed out

./ls | more 2>&1
timed out

Unless you redirect stdout to a file first -- although that's not 
surprising.

# ./ls-test 1>ls.out; cat ls.out
ls | more 2>&1
ls
ls-test
ls.c
ls.out
makefile
tmp

./ls | more 2>&1
ls
ls-test
ls.c
ls.out
makefile
tmp

Here's the system information for the linux-lab machine:

# uname -a
Linux smurf 3.2.0-49-generic #75-Ubuntu SMP Tue Jun 18 17:39:32 UTC 2013 
x86_64 x86_64 x86_64 GNU/Linux

Thoughts?  Does anyone else's ls handle this test case?

-Kyle