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Re: LINENO is affected by sync

From: Greg Wooledge
Subject: Re: LINENO is affected by sync
Date: Wed, 1 Sep 2021 13:09:22 -0400

On Wed, Sep 01, 2021 at 04:52:29PM +0100, David Collier wrote:
> greg - I'm sorry - I assume there is a proper place for me to post
> follow-up info, can you let me know where it is?

On the bug-bash mailing list is fine.  If the script is too big to
post on bug-bash, then it's not useful for debugging anyway.  We'd
need something smaller that we can actually wrap our heads around.

> I could try for a short script, but this thing is a bit like herding eels.
> I narrowed it down to a single line containing 'sync' - but as you say
> that's clearly impossible.
> And to my embarrassment the bug remains unchanged when I comment-out
> the word sync.

OK, good, that's what I would expect.

> !!!!!!!!!!!!!!!Here is a code segment ( I have removed a few == signs so it
> fits across my screen. ):
> echo "================ At this point \$LINENO has correctly counted about
> 2800 lines=========================test @ 2838 $LINENO"
> echo "=== Something makes bash lose a few counts from \$LINENO - in this
> case about nine - no idea how to fix it. ==="
> if ! filesOrSubdirsPresent "${rootOfDummyFsToInstallAPADN}/usr/sbin/*"
> then :
>     if ${G_verbose} ; then echo "Skipping  ${targetAPARN} - nothing found";
> fi
> else :
>     echo "Installing: ${targetAPARN}*"
>     # Do we really want the '-p' option here??? - it corrupts ownership of
> directories!
>     ( cp -dpR "${rootOfDummyFsToInstallAPADN}"/usr/sbin/* ${cpDestFlag}
>  "${targetAPARN}" )
>     # Not sure we can know that there are no .sh or .pl scripts already
> there but with execute off.
>     # but we install so many we can't go round naming them one-by-one.
>     #
>     setExecutabilityOfScriptsInEntireBranch  "${targetAPARN}"   # All of
> our scripts in /usr/sbin do have .sh extensions.
> echo
> "===========================================================================================test
> @ +16  $LINENO"
>     sync
> fi
> echo
> "==========================================================================================test
> @ +20  $LINENO"

I'm guessing filesOrSubdirsPresent and
setExecutabilityOfScriptsInEntireBranch are functions.

> As you can see, four lines further on, and LINENO has gone down by 5 -
> making it 9 too small

My first guess is that it has something to do with those function calls.
Either the fact that bash is calling a function *at all*, or something
that happens specifically in one of those functions, might be throwing
off the count.

IIRC you said you were using bash 5.0, so here's a dumb little test with
bash-5.0 on my system:

unicorn:~$ cat foo

f() {
  : this is f

echo "Point A: line #$LINENO"
echo "Point B: line #$LINENO"
unicorn:~$ ./foo
Point A: line #7
Point B: line #9

This one passes the test, so it's probably not something like "all
functions break LINENO in the caller in bash 5.0".  That would have been
too obvious.

You should look at setExecutabilityOfScriptsInEntireBranch (since that's
the last function call before the problem is observed).  Maybe something
funny happens in there.  You might be able to comment out that function
call and see if that makes the problem vanish.  If it does, then you can
try to pinpoint what part of the function is triggering the problem.

If it doesn't, then I'm at a loss.

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