Weird: unexpected result after piping a sort


 
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# 8  
This is as it should be. Try the following
Code:
rm mylisting
ls -l | sort > mylisting
vi mylisting

And look at the size of mylisting. This should give a clue of what is going on.
# 9  
Thanks.
Like I said, to me the problem is not to get the list. I am sure I would find other ways, like the one you mention.

The issue is to understand exactly why this is a normal result and expected.

-S
# 10  
What I mean is that if you use ls -l instead of ls and look at whay is inside mylisting you'll notice that the size of the file at the time of the ls -l command is 0.
# 11  
Code:
$ rm * ; touch a b c ; bash -c "ls | sort > out" ; cat out
a
b
c
$ rm * ; touch a b c ; bash -c "ls | sort > out" ; cat out
a
b
c
$ rm * ; touch a b c ; bash -c "ls | sort > out" ; cat out
a
b
c
out
$

Sometimes I get it. Sometimes I don't. To implement the pipeline, the shell has two processes, one for ls and one for sort. There is no guarantee that the ls process will complete the directory read before the sort process opens its output file. It's a race condition that results in variable results. put the output file in another directory.

If you don't get variable results, try other shells or other platforms with more cpu's available. Or vary the other workload that the system is running while it runs your pipeline.

Anyway, ls sorts its output by itself.
This User Gave Thanks to Perderabo For This Post:
# 12  
@Scrutinizer:

Zero size of file initialy.
I get the idea I think... However, it's still counterintuitive.
... or not.
I guess the system creates the file first in order to store the list.
-S

---------- Post updated at 03:18 PM ---------- Previous update was at 03:15 PM ----------

@ Perderabo:
I see....
Thanks !
# 13  
if you redirect the output of ls into a file it seems to always add the name of the file you redirected into the output.
You can try this:

Code:
 ls|sort | grep -v mylisting > mylisting

I think redirections are always determined before actual command execution takes place; after `ls` is executed mylisting is already present in the output before the pipe to sort.
# 14  
The OP was interested in why this phenomenon occurs, rather than the list itself. As Perderabo pointed out about this particular case, the output of ls without operands is sorted by default, so
Code:
ls > mylisting

should provide the right result in this case...
 

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