[Fwd: Re: perl test fails]
Rob Clack
rnc@sanger.ac.uk
Fri Aug 29 10:45:00 GMT 2003
Hooray, we're there! Thank you!
The -x operator works perfectly, but the problem was still rather
obscure, so here's the answer.
Cygwin 1.3.22-1 under NT4, Perl 5.8.0
My script was almost identical to the one Elfyn supplied below, it just
tested a local file rather than /usr/bin/perl.
#!/bin/perl
if ( -x "script" )
{
print "script is executable\n";
}
else
{
system("./script");
}
This local file was a one-liner containing only
echo "I damn well am!"
I had chmod +x this file and when I ran either it or my perl script at
the command prompt I got the output "I damn well am!", indicating that
the -x operator considered the file to be not executable, but the file
itself could, actually, be executed.
But Elfyn's script worked, and mine didn't, so I started poking around.
To my surprise I found that the local file had 644 permissions, not 744
as I'd expected. I chmod +x it again, but the permissions didn't
change, though I could still run it and get the echoed output. I tried
chmod 777, still with no effect. Only when I added a first line
#!/bin/bash would chmod +x work, after which my perl script worked just
like Elfyn's
So there seems to be a couple of weensy buggettes there, though I'm not
suggesting anyone bother to fix them unless they happen to be working
there anyway. They're not serious bugs, but they did obscure the real
problem and waste quite a lot of my and several other people's time.
1. chmod should surely change the permissions whatever the contents of
the file, and if it doesn't, it should issue a message. Silent failure
is not very friendly.
2. a file without execute permission shouldn't execute.
Anyhow, thanks for all the responses.
Rob
Elfyn McBratney wrote:
> Rob Clack wrote:
>
>>Well I thought maybe I'd better just try setting $CYGWIN, even though it
>>didn't seem relevant (I don't have "..problems with NT shares or Samba
>>drives..", since the script reliably breaks when run from a local,
>>non-shared drive) and indeed, it made no difference. Unless there's
>>some special way I should be setting it. I just entered
>>CYGWIN=nosmbntsec at the dollar prompt.
>>
>>OK, so if I assume by the silence that -x is broken, can anyone suggest
>>how I can determine in a perl script whether or not a file is executable?
>
>
> The `-x' operator WFM. Does, say, this script fail for you (make sure perl
> is *actually* executable) ?
>
> #!/usr/bin/perl
>
> if (-x "/usr/bin/perl") {
> print "yupp, perl is executable.\n";
> } else {
> print "ut-oh! perl isn't executable.\n";
> }
>
> If you haven't already posted cygcheck[1] output, that might help, and also
> post your script (I couldn't find it in my archives). Sorry if you've
> already done this.
>
> -- Elfyn
>
> [1] non-inline, plain-text attachment, as per <http://cygwin.com/problems.html>
>
>>------------- hyphens to separate this from previous posts -------------
>>
>>Thank you Igor. However, I've now read the entry on smbntsec and it
>>doesn't seem relevant. (Was a useful exercise in itself, since I didn't
>>know about the CYGWIN env var either ;)) I don't have a problem on the
>>Linux box, only on the NT one. And it doesn't matter whether I'm running
>>the script from the networked drive or from the local hard drive, I only
>>get the error under Cygwin.
>>
>>So far it keeps looking to me as though Cygwin is broken.
>>
>>Igor Pechtchanski wrote:
>>
>>>On Wed, 27 Aug 2003, Rob Clack wrote:
>>>
>>>
>>>>Hmmm, don't see how it can have anything to do with the mapping of a
>>>>networked drive, since the problem started on the NT4 box, at which time
>>>>the scriptlet was located in /cygdrive/e/cygwin/rnc/try.
>>>>
>>>>Since I wanted to demonstrate that it worked on the Linux box (having
>>>>tripped over that one originally!) each time I hacked one copy of the
>>>>script I then had to move to the other machine and duplicate the changes
>>>>I'd just made. Clearly this was error-prone, so it made sense to just
>>>>use the copy on the Linux box. On the NT4 it's accessible as
>>>>/cygdrive/i/rnc/try.
>>>
>>>Rob,
>>>
>>>Well, it's usually a good idea to keep as many variables fixed as
>>>possible. By sharing the script, you've unknowingly introduced another
>>>variable (that of SMB shares). I'd suggest moving the script back to a
>>>local directory, and simply copying it to the shared drive when you want
>>>to try it on Linux. That way you can reliably reproduce the problem on
>>>the local drive.
>>>
>>>
>>>>And no, I've never heard of smbntsec. What's it mean/do?
>>>
>>>See <http://cygwin.com/cygwin-ug-net/using-cygwinenv.html>. It's on by
>>>default. FYI, it may require very careful hand-maintenance of /etc/passwd
>>>and /etc/group (in fact, I've ended up turning it off because the
>>>maintenance effort wasn't worth it for me). You might wish to add
>>>"nosmbntsec" to your CYGWIN variable.
>>> Igor
>>>
>>>>>At 09:36 AM 8/26/2003, Rob Clack you wrote:
>>>>>
>>>>>
>>>>>
>>>>>>Gerrit
>>>>>>
>>>>>>I've been away for a week, hence the delayed response.
>>>>>>
>>>>>>Thanks for this and clearly my scriptlet was broken. I've now tried
>>>>>>both alternatives as suggested below. Both work perfectly under Linux.
>>>>>>Neither works under NT4.
>>>>>>
>>>>>>Linux output:
>>>>>>
>>>>>>script is executable
>>>>>>
>>>>>>NT4 output:
>>>>>>
>>>>>>I damn well am!
>>>>>>
>>>>>>To eliminate error further, I'm now running just one copy of the
>>>>>>script, since the disk I use on my Linux box is mapped to the i: drive
>>>>>>on the NT4 box.
>>>>>
>>>>>Are you suggesting that you're using a mapped drive from your Linux box?
>>>>>That may be the problem. Do you have 'smbntsec' set in your CYGWIN
>>>>>environment variable?
>
>
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--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Middle age is when broadness of mind and narrowness
of waist change places.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Rob Clack Acedb Development, Informatics Group
email: rnc@sanger.ac.uk Wellcome Trust Sanger Institute
Tel: +44 1223 494780 Wellcome Trust Genome Campus
Fax: +44 1223 494919 Hinxton Cambridge CB10 1SA
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