echo vs. ls race condition?

[Hannu E K Nevalainen]

> 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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