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From: Tad McClellan on 29 Dec 2009 21:29
Wanna-Be Sys Admin <sysadmin(a)example.com> wrote:
> Peng Yu wrote:
>
>> Since my perl is installed in a nonstandard location, I have to use '/
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> usr/bin/env perl'. I also what to use it with '-w'. I'm wondering how
>> to do it.
>>
>> Currently, I have the following error.
>>
>> $ head -n 1 ./main.pl
>> #!/usr/bin/env perl -w
>> $ ./main.pl
>> /usr/bin/env: perl -w: No such file or directory
>
> just use "use warnings;" which offers some advantages. Keep the env the
> same. Problem solved.


Please re-read the problem statement...


--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.liamg\100cm.j.dat/"
From: Ben Morrow on 29 Dec 2009 23:30

Quoth Tad McClellan <tadmc(a)seesig.invalid>:
> Wanna-Be Sys Admin <sysadmin(a)example.com> wrote:
> > Peng Yu wrote:
> >
> >> Since my perl is installed in a nonstandard location, I have to use '/
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >> usr/bin/env perl'. I also what to use it with '-w'. I'm wondering how
> >> to do it.
> >>
> >> Currently, I have the following error.
> >>
> >> $ head -n 1 ./main.pl
> >> #!/usr/bin/env perl -w
> >> $ ./main.pl
> >> /usr/bin/env: perl -w: No such file or directory
> >
> > just use "use warnings;" which offers some advantages. Keep the env the
^^^^^^^^^^^^^^^^
> > same. Problem solved.
^^^^^

....that is, use

#!/usr/bin/env perl

use warnings;

so that the kernel can pass 'perl' as a single argument to env(1) and it
will work as expected.

> Please re-read the problem statement...

Please re-read the solution offered...

:)

(Not that I think this is a good solution. env(1) on the #! line is a
security risk, since you don't know what's in the PATH; I've always
found it a little disconcerting that python recommends

#!/usr/bin/env python

in the standard docs.)

Ben

From: Dr.Ruud on 30 Dec 2009 06:13
RedGrittyBrick wrote:
> Ilya Zakharevich wrote:

>> `use warning' is useful in a module. It is mostly useless in
>> a script. One should always use -w in scripts.
>
> Can anyone provide a reference to where Ilya (or anyone else) provides
> an explanation of this assertion?
>
> It doesn't seem to be in accord with `perldoc perllexwarn`. Am I right
> to assume there is some disagreement on this point?

I prefer -w in scripts too, because it enforces warnings on the included
code.

The 'use warnings' is only lexical, that's all there is to it.

--
Ruud
From: John W. Krahn on 30 Dec 2009 10:29
Dr.Ruud wrote:
> RedGrittyBrick wrote:
>> Ilya Zakharevich wrote:
>
>>> `use warning' is useful in a module. It is mostly useless in
>>> a script. One should always use -w in scripts.
>>
>> Can anyone provide a reference to where Ilya (or anyone else) provides
>> an explanation of this assertion?
>>
>> It doesn't seem to be in accord with `perldoc perllexwarn`. Am I right
>> to assume there is some disagreement on this point?
>
> I prefer -w in scripts too, because it enforces warnings on the included
> code.

Then you probably want to use -W instead of -w.



John
--
The programmer is fighting against the two most
destructive forces in the universe: entropy and
human stupidity. -- Damian Conway
From: Peter J. Holzer on 30 Dec 2009 10:57
On 2009-12-30 11:13, Dr.Ruud <rvtol+usenet(a)xs4all.nl> wrote:
> RedGrittyBrick wrote:
>> Ilya Zakharevich wrote:
>>> `use warning' is useful in a module. It is mostly useless in
>>> a script. One should always use -w in scripts.
>>
>> Can anyone provide a reference to where Ilya (or anyone else) provides
>> an explanation of this assertion?
>>
>> It doesn't seem to be in accord with `perldoc perllexwarn`. Am I right
>> to assume there is some disagreement on this point?
>
> I prefer -w in scripts too, because it enforces warnings on the included
> code.

Which is why I disagree with Ilya and you. -w is mostly useless in a
script and should never be used except maybe as a quick hack during
debugging.


> The 'use warnings' is only lexical, that's all there is to it.


And I think this is a good thing. Getting lots of warnings in code I
haven't written and cannot change[1][2] is not very helpful. And most
modules use "use warnings" anyway, so it's usually redundant (and you
probably should be wary of those that don't use it).

I do think it was a good thing that -w was invented before "use
warnings": It forced module maintainers to clean up their code.

hp

[1] Well, *I* can change it because I'm sysadmin on most of the systems
where my code runs. But that's far from universal.

[2] I remember the bad old days of C programming where you could choose
between getting lots of warnings from system header files and turning
off many useful warnings.
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