Re: Does -s apply to -m in sort?

[Eric Blake]

On 5/11/20 5:01 PM, Eric Blake wrote:

> You also didn't state whether you tried the --debug option, to see if 
> the presence or absence of -s showed enough debugging crumbs to prove 
> that you at least tried to analyze the problem yourself.  Nor did you 
> mention whether you read the source code (it _is_ open source, after 
> all, so instead of asking someone else to do your homework, _you_ can 
> find the answer).

In an effort to teach you how to read source code, and looking at 
coreutils.git commit c7194b43 (current master as I write this), look at 
src/sort.c:

In function main(), there is a getopt_long() loop, where '-m' sets 
'mergeonly = true' (line 4493), and '-s' sets 'stable = true' (line 
4513).  A quick grep shows that:

$ grep -C 10 '\bstable\b' src/sort.c | grep -c mergeonly
0

there are 0 instances of one variable referenced within ten lines of 
locality to the other.  So there are likely no explicit interlocking 
between the two options (that is, turning on one doesn't affect the 
other, they can both be turned on independently).

Next, try to see where things are used.
in main(), if mergeonly is set, we call merge() (line 4752)
in merge(), we unconditionally call mergefiles() (line 3816)
in mergefiles(), we unconditionally call mergefps() (line 3138)
in mergefps(), we unconditionally call compare() (line 2992)
in compare(), the code checks the value of 'stable' if there is a 
keylist (line 2746)

So on that basis alone, yes, -s has effects when -m is used (but more 
importantly, -s only matters when -k is used).

Now, please quit wasting time.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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