RE: echo vs. ls race condition?

[Fred Kulack <kulack at us dot ibm dot com>]

Interesting tests. I still can't get it to fail...

What terminal are you using? Perhaps there's something weird going on with 

flow control as descriptors are dup'd for the utilities there? 
I'm using plain old winblows console.
Did you try the regular echo instead of the builtin? It may have different 
characteristics
with regard to this.

> uname -a
CYGWIN_NT-5.1 kulack 1.5.9(0.112/4/2) 2004-03-18 23:05 i686 unknown 
unknown Cygwin

Bash /kulack/test/test
> cygcheck -cd bash
Cygwin Package Information
Package              Version
bash                 2.05b-16

Bash /kulack/test/test
> echo $CYGWIN


Also, the zz.sh script wouldn't run correctly for me unless I made it used 
the magic number #!/bin/bash,
it was running sh instead of bash and didn't support some of the 
constructs used. 
Some weirdness with sh versus bash mode... I never had to pay much 
attention
to the relationships there, but perhaps that's related to the cause?

Bash /kulack/test/test
> echo $SHELL
/bin/bash



"The stuff we call "software" is not like anything that human society 
  is used to thinking about. Software is something like a machine, and 
  something like mathematics, and something like language, and 
  something like thought, and art, and information... 
  but software is not in fact any of those other things."
Bruce Sterling - The Hacker Crackdown

Fred A. Kulack - IBM eServer iSeries - Enterprise Application Solutions
ERP, Java DB2 access, Jdbc, JTA, etc...
IBM in Rochester, MN  (Phone: 507.253.5982   T/L 553-5982)
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"Hannu E K Nevalainen" <garbage_collector@telia.com> 
Sent by: cygwin-owner@cygwin.com
05/24/2004 03:27 PM

To
<cygwin@cygwin.com>
cc

Subject
RE: echo vs. ls race condition?






> From: Henry S. Thompson
> Sent: Monday, May 24, 2004 6:32 PM

> Fred Kulack <kulack@we.bigblue.xxx> writes:
>
> >> Short summary:  a loop with echo and ls does not produce well-ordered
> >> output
> >
> > For what it's worth, it works fine on my system.
> >         XP Professional
> >         bash                    2.05b-16
> >
> > I always try an update and see if its still happens when I find
> something
> > not quite right.
>
> Thanks for (failing to) reproduce, but I did a complete update before
> reporting, and indeed that _is_ the bash I'm using -- sorry that in my
> first message, I reported what _bash_ itself thinks, as opposed to
> what cygwin thinks.

FWIW; I can reproduce it. It seems to me that it is some kind of problem
with bash's use of subshells in loops (synchronizing output). I have no
knowledge of the internals here, so bear with me.

I've changed your script to be little less (runs shorter time), show 
better
what happens... and also adjusted for the fact that I have a bash function
for "ls" that got in the way. (cause: --classify)

$ md zz && cd zz
$ cat ../zz.sh
x=10
while [ $x -lt 20 ]; do echo -en "\r$x  ";mkdir $x; x=`expr $x + 1`; done
for d in *; do echo -en "\r$d  ";touch $d/aaa-$d; touch $d/bbb-$d; done
command ls -d * | while read d; do echo -e "\n-$d-"; ls $d ; done

NOTE: For me, often the FIRST run after a 'rm -rf *' the script succeeds -
then if you do the following, it fails;

$ command ls -d * | while read d; do echo -e "\n-$d-"; ls $d ; done

-10-
aaa-10  bbb-10

-11-
aaa-11  bbb-11

-12-
aaa-12  bbb-12

-13-
aaa-13  bbb-13

-14-
aaa-14  bbb-14

-15-
aaa-15  bbb-15

-16-
aaa-16  bbb-16

-17-

-18-
aaa-17  bbb-17
aaa-18  bbb-18

-19-
aaa-19  bbb-19


As the following succeeds, I'm lead to believe what I said earlier - not
that it is equivalent though:

$ command ls -d * | while read d; do echo -en "\n-$d-\n$(ls $d)" ; done

-10-
aaa-10
bbb-10

-11-
aaa-11
bbb-11

-12-
aaa-12
bbb-12

-13-
aaa-13
bbb-13

-14-
aaa-14
bbb-14

-15-
aaa-15
bbb-15

-16-
aaa-16
bbb-16

-17-
aaa-17
bbb-17

-18-
aaa-18
bbb-18

-19-
aaa-19
bbb-19


All this seems somehow be triggered by the fact that diskcaching plays a
role here: i.e. the first run has this "time" output;
                 real    0m5.385s
                 user    0m2.040s
                 sys     0m3.670s
the second run and forth;
                 real    0m1.233s
                 user    0m0.420s
                 sys     0m0.850s
(w some tiny differences).

 I have tried to use { _list_of_commands_ } as described in the bash 
manual;
i.e, this runs, but has the same problem:

$ command ls -d * | while read d; do { echo -e "\n-$d-"; ls $d ; } ; done

The idea is to force 'do _list_ ;done' to be executed in the "local" 
shell,
not a subshell. I've tried other variants of it, but have failed to make 
it
work;
 Here I wonder: Is that yet another of those irritating
documentation-failure(-to-understand) issues that I stumble on quite 
often?


$ uname -a
CYGWIN_NT-5.0 P450 1.5.10s(0.115/4/2) 20040519 13:51:37 i686 unknown 
unknown
Cygwin

$ cygcheck -cd bash
Cygwin Package Information
Package              Version
bash                 2.05b-16

$ echo $CYGWIN
notitle glob check_case:strict server=1

Tests run on a FAT32 partition on a P2/450Mhz, W2K adv server, SP4++ - if
that has any influence.


/Hannu E K Nevalainen, B.Sc. EE - 59+16.37'N, 17+12.60'E

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