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Content-Type: text/plain;
charset="us-ascii"
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Hi All



Perl script works without the first line ( perl Interpreter
: #! /usr/bin/perl) . What is the real use of this line ? This line does
not through any error on Windows where , this path does not exist .

Why is it so ?



Could anybody explain it clearly?



Thanks

Sunita


------_=_NextPart_001_01CBABD0.FA4ED37D--

Thats called Sha-Bang header also called Magical Bytes.

They come into picture when you do not specify the interpreter while
executing the script.

EG: ./my_script.pl (here no interpreter is specified i.e perl is missing)

In this case, script uses the interpreter specified at sha-bang header.

And now since you are specifying the interpreter on the prompt (perl
my_script.pl) hence its not showing any error even on windows.

Cheers,
Parag




On Mon, Jan 3, 2011 at 9:33 PM, Sunita Rani Pradhan
<Sunita.Pradhan [at] altair.com> wrote:
> Hi All
>
>
>
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0Perl script =C2=A0works without =
the first line ( perl Interpreter
> : #! /usr/bin/perl) . What is the real use of this line ? This line does
> not through any error on Windows where , this path does not exist .
>
> Why is it so ?
>
>
>
> Could anybody explain it =C2=A0clearly?
>
>
>
> Thanks
>
> Sunita
>
>

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On 1/4/11 12:33 AM, Sunita Rani Pradhan wrote:
> Perl script works without the first line ( perl Interpreter
> : #! /usr/bin/perl) . What is the real use of this line ? This line does
> not through any error on Windows where , this path does not exist .

On Unix, it allows you to run your script with just the scripts filename
rather than running the interpreter and passing the filename as an
argument. "./myscript" instead of "perl myscript".

On Windows, that line is just a comment. Neither the operating system
nor the interpreter does anything with it. To run a script with just
the name, you need to use a file extension associated with the Perl
interpreter. The standard extension is ".pl", though in principle you
could use something else. If you don't have corporate overlords forcing
you to use something else, just use ".pl".

I would, however, recommend that you use the "#!/usr/bin/perl" line even
on Windows. It will make things a little easier if you have to move the
script over to a Unix like system. It won't cause any problems in
windows, it will just get skipped right over.

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You can put any path in that line, not only /usr/bin/perl.

If you are using Perl under Windows, you may want to put paths like:

#!C:/perl/bin/perl
#!C:/perl/bin/perl.exe

If a Perl program uses this line under Unix/Linux and if the program is
executable, it can be ran by just using:

../program_name

without needing to use
perl program_name

Under Windows it doesn't help that line at all if you just need to run the
programs from a command line.

But it can help you if you need to run Perl programs as CGI scripts with
Apache.

I have Apache installed on E: drive and Perl on the same drive in the folder
e:\usr
and in this case I can use

#!/usr/bin/perl

as the first line in CGI scripts
(although I haven't used CGI scripts for years:)

--Octavian

----- Original Message -----
From: "Sunita Rani Pradhan" <Sunita.Pradhan [at] altair.com>
To: <beginners [at] perl.org>
Sent: Tuesday, January 04, 2011 7:33 AM
Subject: 1st line of perl script


Hi All



Perl script works without the first line ( perl Interpreter
: #! /usr/bin/perl) . What is the real use of this line ? This line does
not through any error on Windows where , this path does not exist .

Why is it so ?



Could anybody explain it clearly?



Thanks

Sunita



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I think this is very good info .. I have tried on Windows and Unix as =
well .
- I found like , this line does not matter on windows . Windows need .pl =
extension but Unix/Linux does not .

- Unix required this interpreter line when we are executing as , e.g =
../test.pl or ./test.

If the line is not given then inside script running on Unix , then need =
to execute it using perl interpreter externally .


Thank you All .

-Sunita

-----Original Message-----
From: alanhaggai [at] gmail.com [mailto:alanhaggai [at] gmail.com] On Behalf Of =
Alan Haggai Alavi
Sent: Tuesday, January 04, 2011 11:16 AM
To: Sunita Rani Pradhan
Cc: beginners [at] perl.org
Subject: Re: 1st line of perl script

Hi Sunita,

> =A0 =A0 =A0 =A0 =A0 =A0Perl script =A0works without the first line ( =
perl Interpreter
> : #! /usr/bin/perl) . What is the real use of this line ? This line =
does
> not through any error on Windows where , this path does not exist .

It is a shebang line which is only useful in Unix-like operating
systems. In such systems, the shebang line should start in the first
column of the first line. When such a script with its executable bit
set is run by itself, the operating systems checks for the shebang
line to see which interpreter should be used for executing the script.

However, in Windows (and other non-Unix-like operating systems), the
shebang is usually considered a comment and skipped. Instead of the
shebang line, such systems depend on file extension associations or
explicit invocation of the script using the interpreter.

For more details, see: http://en.wikipedia.org/wiki/Shebang_(Unix)

Regards,
Alan Haggai Alavi.
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On Tue, 04 Jan 2011 01:09:56 -0500, George Worroll wrote:
> On Windows, that line is just a comment. Neither the operating system
> nor the interpreter does anything with it.

Not quite. Any options on the line (e.g., -T) will be activated.

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Hi Sunita,

> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0Perl script =C2=A0works without =
the first line ( perl Interpreter
> : #! /usr/bin/perl) . What is the real use of this line ? This line does
> not through any error on Windows where , this path does not exist .

It is a shebang line which is only useful in Unix-like operating
systems. In such systems, the shebang line should start in the first
column of the first line. When such a script with its executable bit
set is run by itself, the operating systems checks for the shebang
line to see which interpreter should be used for executing the script.

However, in Windows (and other non-Unix-like operating systems), the
shebang is usually considered a comment and skipped. Instead of the
shebang line, such systems depend on file extension associations or
explicit invocation of the script using the interpreter.

For more details, see: http://en.wikipedia.org/wiki/Shebang_(Unix)

Regards,
Alan Haggai Alavi.
--
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At 01:09 -0500 04/01/2011, George Worroll wrote:


>On 1/4/11 12:33 AM, Sunita Rani Pradhan wrote:
>> Perl script works without the first line ( perl Interpreter
>>: #! /usr/bin/perl) . What is the real use of this line ? This line does
>>not through any error on Windows where , this path does not exist .
>
>On Unix, it allows you to run your script with just the scripts
>filename rather than running the interpreter and passing the
>filename as an argument. "./myscript" instead of "perl myscript".
>
>On Windows, that line is just a comment...

On UNIX/ Mac OS X it also gives you the option of using a variety of
perl installations. For example the Apple installation of Perl is
made in /usr/bin but the default installation is in /usr/local/bin
and other programs might make further installations in, say,
/opt/local/bin/...

....so if I run this script:

#!/usr/bin/perl
use strict;
print "Perl Version: $^V\n";
print "\ [at] INC:\n" . join $/, [at] INC;

I will get this:

Perl Version: v5.10.0
[at] INC:
/Users/jd
/Library/Perl/Updates/5.10.0/darwin-thread-multi-2level
/Library/Perl/Updates/5.10.0
/System/Library/Perl/5.10.0/darwin-thread-multi-2level
/System/Library/Perl/5.10.0
/Library/Perl/5.10.0/darwin-thread-multi-2level
/Library/Perl/5.10.0
/Network/Library/Perl/5.10.0/darwin-thread-multi-2level
/Network/Library/Perl/5.10.0
/Network/Library/Perl
/System/Library/Perl/Extras/5.10.0/darwin-thread-multi-2leve l
/System/Library/Perl/Extras/5.10.0
..


but if I install a later version and want to bypass the Apple (or
other) installation altogether then I can change the shebang as
follows:

#!/usr/local/bin/perl
use strict;
print "Perl Version: $^V\n";
print "\ [at] INC:\n" . join $/, [at] INC;

and get:

Perl Version: v5.12.2
[at] INC:
/Users/jd
/usr/local/lib/perl5/site_perl/5.12.2/darwin-2level
/usr/local/lib/perl5/site_perl/5.12.2
/usr/local/lib/perl5/5.12.2/darwin-2level
/usr/local/lib/perl5/5.12.2
..


JD


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On 1/4/11 4:31 AM, John Delacour wrote:
> On UNIX/ Mac OS X it also gives you the option of using a variety of
> perl installations. For example the Apple installation of Perl is
> made in /usr/bin but the default installation is in /usr/local/bin and
> other programs might make further installations in, say,
> /opt/local/bin/...

Very good point. The Perl team does at times intentionally break
backwards compatability because they feel the old way was simply wrong.
And it's always possible they'll do so accidentally, especially for more
tricky ways of doing things. If you've got mission critical stuff
running on Perl, keeping the old version around and accessible, at least
for a while after the upgrade, is a good idea- and shebang makes it easy
to support both as long as you need to. If you get to hacking the
interpreter itself, you absolutely need a way to access the canonical
version because at some point you will break the one you are hacking
on. Hopefully you'll fix what you broke, but you don't want to be
without Perl during that phase.

Keeping the old version around and accessible- actually, that's probably
a reasonable justification for using Windows file extensions other than
..pl. Associate that to whichever version is your sites primary Perl
installation, and associate something else(.prl for instance) to the
secondary installation. Just make sure to have a standard for which
extension calls which interpreter, or things will get confusing.
Including a shebang on windows for documentation purposes, so people
reading the code know what interpreter is supposed to get it, is a good
idea even though it's not used by the system.

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On Jan 4, 2011, at 12:09 AM, George Worroll wrote:

> I would, however, recommend that you use the "#!/usr/bin/perl" line =
even on Windows. It will make things a little easier if you have to =
move the script over to a Unix like system. It won't cause any problems =
in windows, it will just get skipped right over.

Although I don't know if this works on Windows, I notice that nobody has =
mentioned...

#!/usr/bin/env perl

.... which invokes the perl that comes first in one's $PATH, making the =
script more portable, and also easing the management of having multiple =
Perls installed.

It's discussed here: <http://www.perlmonks.org/?node_id=3D716740>

Chap=

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On 11-01-04 02:56 PM, Chap Harrison wrote:
> Although I don't know if this works on Windows, I notice that nobody has mentioned...
>
> #!/usr/bin/env perl

No, it doesn't. In the Windows Registry, the *.pl extension is linked
to the perl program. Double-clicking on a *.pl file will run perl with
it as an argument. It ignores the shebang line.

Except...

Some web servers read the shebang line to determine what program to run
a CGI with. If you are running a server in Windows, make sure the
shebang line of your CGIs points to a valid program.

Example:

!#C:\PERL\BIN\PERL.EXE


--
Just my 0.00000002 million dollars worth,
Shawn

Confusion is the first step of understanding.

Programming is as much about organization and communication
as it is about coding.

The secret to great software: Fail early & often.

Eliminate software piracy: use only FLOSS.

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I think there is no error thrown by Windows (or any other architecture)
because this line is never compiled because of the # in front which
signifies the line as comments.

On Tue, 04 Jan 2011 00:33:18 -0500, Sunita Rani Pradhan
<Sunita.Pradhan [at] altair.com> wrote:

> Hi All
>
>
> Perl script works without the first line ( perl Interpreter
> : #! /usr/bin/perl) . What is the real use of this line ? This line does
> not through any error on Windows where , this path does not exist .
>
> Why is it so ?
>
>
> Could anybody explain it clearly?
>
>
> Thanks
>
> Sunita
>


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We have -w option for warnings which we specify with the 1st line . How
does it work on windows ?

-Sunita

-----Original Message-----
From: Donald Calloway [mailto:donald.calloway [at] gmail.com]
Sent: Sunday, January 09, 2011 6:42 PM
To: beginners [at] perl.org
Subject: Re: 1st line of perl script

I think there is no error thrown by Windows (or any other architecture)

because this line is never compiled because of the # in front which
signifies the line as comments.

On Tue, 04 Jan 2011 00:33:18 -0500, Sunita Rani Pradhan
<Sunita.Pradhan [at] altair.com> wrote:

> Hi All
>
>
> Perl script works without the first line ( perl
Interpreter
> : #! /usr/bin/perl) . What is the real use of this line ? This line
does
> not through any error on Windows where , this path does not exist .
>
> Why is it so ?
>
>
> Could anybody explain it clearly?
>
>
> Thanks
>
> Sunita
>


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Maybe you can use "use warnings;" for this ...

Best regards
Christian




Am 10.01.11 13:49 schrieb "Sunita Rani Pradhan" unter
<Sunita.Pradhan [at] altair.com>:

>We have -w option for warnings which we specify with the 1st line . How
>does it work on windows ?
>
>-Sunita
>
>-----Original Message-----
>From: Donald Calloway [mailto:donald.calloway [at] gmail.com]
>Sent: Sunday, January 09, 2011 6:42 PM
>To: beginners [at] perl.org
>Subject: Re: 1st line of perl script
>
>I think there is no error thrown by Windows (or any other architecture)
>
>because this line is never compiled because of the # in front which
>signifies the line as comments.
>
>On Tue, 04 Jan 2011 00:33:18 -0500, Sunita Rani Pradhan
><Sunita.Pradhan [at] altair.com> wrote:
>
>> Hi All
>>
>>
>> Perl script works without the first line ( perl
>Interpreter
>> : #! /usr/bin/perl) . What is the real use of this line ? This line
>does
>> not through any error on Windows where , this path does not exist .
>>
>> Why is it so ?
>>
>>
>> Could anybody explain it clearly?
>>
>>
>> Thanks
>>
>> Sunita
>>
>
>
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>
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>
>
>
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>
>


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Yes I can use that . Does this -w option works on windows or not ?

-----Original Message-----
From: Christian Marquardt [mailto:Christian.Marquardt [at] trivadis.com]
Sent: Monday, January 10, 2011 6:22 PM
To: Sunita Rani Pradhan; Donald Calloway; beginners [at] perl.org
Subject: Re: 1st line of perl script

Maybe you can use "use warnings;" for this ...

Best regards
Christian




Am 10.01.11 13:49 schrieb "Sunita Rani Pradhan" unter
<Sunita.Pradhan [at] altair.com>:

>We have -w option for warnings which we specify with the 1st line .
How
>does it work on windows ?
>
>-Sunita
>
>-----Original Message-----
>From: Donald Calloway [mailto:donald.calloway [at] gmail.com]
>Sent: Sunday, January 09, 2011 6:42 PM
>To: beginners [at] perl.org
>Subject: Re: 1st line of perl script
>
>I think there is no error thrown by Windows (or any other architecture)
>
>because this line is never compiled because of the # in front which
>signifies the line as comments.
>
>On Tue, 04 Jan 2011 00:33:18 -0500, Sunita Rani Pradhan
><Sunita.Pradhan [at] altair.com> wrote:
>
>> Hi All
>>
>>
>> Perl script works without the first line ( perl
>Interpreter
>> : #! /usr/bin/perl) . What is the real use of this line ? This line
>does
>> not through any error on Windows where , this path does not exist .
>>
>> Why is it so ?
>>
>>
>> Could anybody explain it clearly?
>>
>>
>> Thanks
>>
>> Sunita
>>
>
>
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>
>
>
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>
>


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On 11-01-10 10:21 AM, Sunita Rani Pradhan wrote:
> Yes I can use that . Does this -w option works on windows or not ?

I do believe so but if you `use warnings;` you can turn it off. You
can't do that with -w.

use warnings;

{
no warnings;
# some code
}


--
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Shawn

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as it is about coding.

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On Mon, Jan 10, 2011 at 10:32 AM, Shawn H Corey <shawnhcorey [at] gmail.com> wro=
te:
> I do believe so but if you `use warnings;` you can turn it off. =C2=A0You=
can't
> do that with -w.

I just tested with Strawberry Perl v5.12.1 in Windows XP with the
following code:

#!/usr/bin/perl -w

my [at] a;
my $b =3D [at] a[0];

__END__

When run, I get:

Scalar value [at] a[0] better written as $a[0] at test.pl line 4.

So yes, it does seem to work, but I think that 'use warnings;' is best
practice anyway, as Shawn pointed out.

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Yes I agree . Then I am coming back to my 1st question . This path does =
not exist on windows "/usr/bin/perl " , how it works ?


Thanks
Sunita

-----Original Message-----
From: Brandon McCaig [mailto:bamccaig [at] gmail.com]
Sent: Monday, January 10, 2011 9:14 PM
To: Shawn H Corey
Cc: beginners [at] perl.org
Subject: Re: 1st line of perl script

On Mon, Jan 10, 2011 at 10:32 AM, Shawn H Corey <shawnhcorey [at] gmail.com> =
wrote:
> I do believe so but if you `use warnings;` you can turn it off. =A0You =
can't
> do that with -w.

I just tested with Strawberry Perl v5.12.1 in Windows XP with the
following code:

#!/usr/bin/perl -w

my [at] a;
my $b =3D [at] a[0];

__END__

When run, I get:

Scalar value [at] a[0] better written as $a[0] at test.pl line 4.

So yes, it does seem to work, but I think that 'use warnings;' is best
practice anyway, as Shawn pointed out.

--
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It doesn't, the line starts with a '#' so it is ignored. You have to =
tell MS-Windows to associate .pl files with perl.exe. Then the OS does =
what #! was supposed to. But it will always use the same copy of =
perl.exe, so you don't get the ability to use different releases for =
different scripts.

Bob McConnell

-----Original Message-----
From: Sunita Rani Pradhan [mailto:Sunita.Pradhan [at] altair.com]
Sent: Monday, January 10, 2011 10:58 AM
To: Brandon McCaig; Shawn H Corey
Cc: beginners [at] perl.org
Subject: RE: 1st line of perl script

Yes I agree . Then I am coming back to my 1st question . This path does =
not exist on windows "/usr/bin/perl " , how it works ?


Thanks
Sunita

-----Original Message-----
From: Brandon McCaig [mailto:bamccaig [at] gmail.com]
Sent: Monday, January 10, 2011 9:14 PM
To: Shawn H Corey
Cc: beginners [at] perl.org
Subject: Re: 1st line of perl script

On Mon, Jan 10, 2011 at 10:32 AM, Shawn H Corey <shawnhcorey [at] gmail.com> =
wrote:
> I do believe so but if you `use warnings;` you can turn it off. =A0You =
can't
> do that with -w.

I just tested with Strawberry Perl v5.12.1 in Windows XP with the
following code:

#!/usr/bin/perl -w

my [at] a;
my $b =3D [at] a[0];

__END__

When run, I get:

Scalar value [at] a[0] better written as $a[0] at test.pl line 4.

So yes, it does seem to work, but I think that 'use warnings;' is best
practice anyway, as Shawn pointed out.

--
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On 11-01-10 10:57 AM, Sunita Rani Pradhan wrote:
> Yes I agree . Then I am coming back to my 1st question . This path does not exist on windows "/usr/bin/perl " , how it works ?

It doesn't. At least, it doesn't if you start the script from Windows.
What Windows does is look up the extension, *.pl, in the Registry and
launch the program associated with it. When it starts, perl will check
the first line for any switches (options in UNIX talk) and sets them.

However, some web servers read the the shebang line and executes what it
says. So, you should change any Perl CGIs to point to the perl program.


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On Mon, Jan 10, 2011 at 11:07 AM, Shawn H Corey <shawnhcorey [at] gmail.com> wro=
te:
> It doesn't. =C2=A0At least, it doesn't if you start the script from Windo=
ws.
> =C2=A0What Windows does is look up the extension, *.pl, in the Registry a=
nd
> launch the program associated with it. =C2=A0When it starts, perl will ch=
eck the
> first line for any switches (options in UNIX talk) and sets them.
>
> However, some web servers read the the shebang line and executes what it
> says. =C2=A0So, you should change any Perl CGIs to point to the perl prog=
ram.

It isn't used to determine the interpreter on Windows, but it is still
apparently always "examined" for command line options, regardless of
platform.

perldoc perlrun:
> The #! line is always examined for switches as the line is being parsed.
> Thus, if you=E2=80=99re on a machine that allows only one argument with t=
he #!
> line, or worse, doesn=E2=80=99t even recognize the #! line, you still can=
get
> consistent switch behavior regardless of how Perl was invoked, even if
> -x was used to find the beginning of the program.

I guess see `perldoc perlrun` for the full story.

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On 11-01-10 11:15 AM, Brandon McCaig wrote:
> On Mon, Jan 10, 2011 at 11:07 AM, Shawn H Corey<shawnhcorey [at] gmail.com> wrote:
>> However, some web servers read the the shebang line and executes what it
>> says. So, you should change any Perl CGIs to point to the perl program.
>
> It isn't used to determine the interpreter on Windows, but it is still
> apparently always "examined" for command line options, regardless of
> platform.

It isn't used if you start your scripts from Windows.

But CGIs are started by the web server and some *do* look at the shebang
line for the interpreter. For CGIs, make sure it has a valid program to
run.


--
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Shawn

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Programming is as much about organization and communication
as it is about coding.

The secret to great software: Fail early & often.

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On Mon, Jan 10, 2011 at 11:21 AM, Shawn H Corey <shawnhcorey [at] gmail.com> wrote:
> It isn't used if you start your scripts from Windows.

It worked for me earlier:

On Mon, Jan 10, 2011 at 10:43 AM, Brandon McCaig <bamccaig [at] gmail.com> wrote:
> I just tested with Strawberry Perl v5.12.1 in Windows XP with the
> following code:
>
> #!/usr/bin/perl -w
>
> my [at] a;
> my $b = [at] a[0];
>
> __END__
>
> When run, I get:
>
> Scalar value [at] a[0] better written as $a[0] at test.pl line 4.

Invoked like: perl test.pl

If I remove the -w from the shebang line then no warning is output.
Unless I'm misunderstanding you...

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And I repeat, it doesn't. Windows looks up the association you defined
and then goes through the %PATH% in your environment looking for the
first perl.exe it can find. It doesn't even read the file, but passes it
as a parameter to perl.exe. At that point, it is up to the Perl
interpreter to decide what to do with that first line.

Bob McConnell

-----Original Message-----
From: Shawn H Corey [mailto:shawnhcorey [at] gmail.com]
Sent: Monday, January 10, 2011 11:08 AM
To: beginners [at] perl.org
Subject: Re: 1st line of perl script

On 11-01-10 10:57 AM, Sunita Rani Pradhan wrote:
> Yes I agree . Then I am coming back to my 1st question . This path
does not exist on windows "/usr/bin/perl " , how it works ?

It doesn't. At least, it doesn't if you start the script from Windows.
What Windows does is look up the extension, *.pl, in the Registry and
launch the program associated with it. When it starts, perl will check
the first line for any switches (options in UNIX talk) and sets them.

However, some web servers read the the shebang line and executes what it

says. So, you should change any Perl CGIs to point to the perl program.


--
Just my 0.00000002 million dollars worth,
Shawn

Confusion is the first step of understanding.

Programming is as much about organization and communication
as it is about coding.

The secret to great software: Fail early & often.

Eliminate software piracy: use only FLOSS.

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On 11-01-10 11:34 AM, Bob McConnell wrote:
> And I repeat, it doesn't. Windows looks up the association you defined
> and then goes through the %PATH% in your environment looking for the
> first perl.exe it can find. It doesn't even read the file, but passes it
> as a parameter to perl.exe. At that point, it is up to the Perl
> interpreter to decide what to do with that first line.


Except for some web servers; they do use the shebang line.


--
Just my 0.00000002 million dollars worth,
Shawn

Confusion is the first step of understanding.

Programming is as much about organization and communication
as it is about coding.

The secret to great software: Fail early & often.

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On 11-01-10 11:29 AM, Brandon McCaig wrote:
> Invoked like: perl test.pl
>
> If I remove the -w from the shebang line then no warning is output.
> Unless I'm misunderstanding you...

It's the Perl interpreter that looks up the switches on the shebang
line, not Windows.


--
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Shawn

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Programming is as much about organization and communication
as it is about coding.

The secret to great software: Fail early & often.

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On Mon, Jan 10, 2011 at 11:39 AM, Shawn H Corey <shawnhcorey [at] gmail.com> wrote:
> It's the Perl interpreter that looks up the switches on the shebang line,
> not Windows.

That's what I've been saying...

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From: "Sunita Rani Pradhan" <Sunita.Pradhan [at] altair.com>
> We have -w option for warnings which we specify with the 1st line . =
How
> does it work on windows ?
>
> -Sunita


Yes it works under Windows, but is recommended to not use it anymore.

It is better to use (under any OS) instead:

use warnings;

Because later in some blocks of code if you'll want you will be able to =
use:

no warnings;

Of course, if you use the -w switch you will be still able to use
no warnings;
later, but it is not nice to begin by using -w then use "no warnings;".

Octavian




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From: "Shawn H Corey" <shawnhcorey [at] gmail.com>
> On 11-01-10 10:21 AM, Sunita Rani Pradhan wrote:
>> Yes I can use that . Does this -w option works on windows or not ?
>
> I do believe so but if you `use warnings;` you can turn it off. You
> can't do that with -w.
>
> use warnings;
>
> {
> no warnings;
> # some code
> }
>



Well, you can use:

#!/usr/bin/perl -w

{
no warnings;
print $ok;
}

It will work and it won't print the warning.

The -w switch work, but the -W switch doesn't accept using "no =
warnings;".

But anyway, using

use warnings;

is recommended because it is cleaner to use

use warnings;
#and
no warnings;

then to use the -w switch and then eventually "no warnings;".

And the shebang line is not required in that case. For example, I =
haven't used it for years.

Octavian


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From: "Bob McConnell" <rvm [at] CBORD.com>

It doesn't, the line starts with a '#' so it is ignored. You have to =
tell MS-Windows to associate .pl files with perl.exe. Then the OS does =
what #! was supposed to. But it will always use the same copy of =
perl.exe, so you don't get the ability to use different releases for =
different scripts.

Bob McConnell



Well, not exactly ignored.
Here is a sample zzz.pl script:

#!/usr/foo/bar -w
print "ok";

Normally, if the shebang line would be really ignored, the program =
should run fine if the program is ran using:

perl zzz.pl

But the result is:

E:\>perl zzz.pl
Can't exec /usr/foo/bar at zzz.pl line 1.

Here is another sample script:

#!/python27/python.exe
import sys
print(sys.copyright)

And here I ran it with Perl:

E:\>perl zzz.pl
E:\>Copyright (c) 2000-2010 ActiveState Software Inc.
Copyright (c) 2001-2010 Python Software Foundation.
....

So even though the program is ran using the Perl interpreter, when it =
finds the shebang line, even under Windows, it executes the program =
using the interpreter found in that line, no matter it is not even Perl.

But this is because Perl is smarter than Python for this thing.

Here is a Perl code I put in the file zzz.py:

#!/usr/bin/perl
use CGI;
print $CGI::VERSION;

If I run it with Python, see what happends:

E:\>python zzz.py
File "zzz.py", line 2
use CGI;
^
SyntaxError: invalid syntax

So it means that Python doesn't parse the shebang line and run the =
program with the program from it.

Which thing is better?

Perl is smarter, but it might be too smart and can create confusion for =
newbies.


For example, the program will give an error if it will have a shebang =
line with a non-existent path like:

#!/foo/bar/baz

But it won't give an error when using a shebang like:

#!/foo/sperlito/bar

and neither when using one like:

#!/foo/bar/baz/who/knows/others/perl/ok/zuzu

because these paths contain the string "perl" (probably).

So a shebang line like

#!perl

is enough if you want to use those switches.

Octavian


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On Mon, Jan 10, 2011 at 11:21 AM, Shawn H Corey <shawnhcorey [at] gmail.com>
wrote:
> It isn't used if you start your scripts from Windows.

It worked for me earlier:

On Mon, Jan 10, 2011 at 10:43 AM, Brandon McCaig <bamccaig [at] gmail.com>
wrote:
> I just tested with Strawberry Perl v5.12.1 in Windows XP with the
> following code:
>
> #!/usr/bin/perl -w
>
> my [at] a;
> my $b =3D [at] a[0];
>
> __END__
>
> When run, I get:
>
> Scalar value [at] a[0] better written as $a[0] at test.pl line 4.

Invoked like: perl test.pl

>> Invoking like this , you are specifying perl interpreter , is not it?
Then why do we need 1st line ? Only test.pl also run this program .

If I remove the -w from the shebang line then no warning is output.
Unless I'm misunderstanding you...

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<bamccaig [at] castopulence.org>

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