s/ / /; - doing harm ?

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Hello,

Please, consider the following short script.
#-----------------------------------------------------
$_ =3D '';

s// /; ## if any of these two lines is commented out,
s/ / /; ## the printed result wil be ok, i.e. '=3D =3D' WHY ?

$_ =3D '';
s// /;
print "=3D$_=3D\n"; ## prints incorrect '=='
#-----------------------------------------------------

This was tested on Win'XT ActivePerl 5.8.8. and 5.8.9.

What is wrong ?

Thanks for any hints,

Stanislaw Romanski
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Re: s/ / /; - doing harm ?

Stanislaw Romanski wrote:
> Hello,
>
> Please, consider the following short script.
> #-----------------------------------------------------
> $_ = '';
>
> s// /; ## if any of these two lines is commented out,
> s/ / /; ## the printed result wil be ok, i.e. '= =' WHY ?
>
> $_ = '';
> s// /;
> print "=$_=\n"; ## prints incorrect '=='
> #-----------------------------------------------------
>
> This was tested on Win'XT ActivePerl 5.8.8. and 5.8.9.
>
> What is wrong ?

If you check the perlop pod under s///, you should find this:
"If the pattern evaluates to the empty string, the last
successfully executed regular expression is used instead."
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Re: s/ / /; - doing harm ?

----- Original Message -----
From: "Bill Luebkert"
To: "Stanislaw Romanski"
Cc:
Sent: Tuesday, June 09, 2009 9:41 AM
Subject: Re: s/ / /; - doing harm ?


> Stanislaw Romanski wrote:
>> Hello,
>>
>> Please, consider the following short script.
>> #-----------------------------------------------------
>> $_ = '';
>>
>> s// /; ## if any of these two lines is commented out,
>> s/ / /; ## the printed result wil be ok, i.e. '= =' WHY ?
>>
>> $_ = '';
>> s// /;
>> print "=$_=\n"; ## prints incorrect '=='
>> #-----------------------------------------------------
>>
>> This was tested on Win'XT ActivePerl 5.8.8. and 5.8.9.
>>
>> What is wrong ?
>
> If you check the perlop pod under s///, you should find this:
> "If the pattern evaluates to the empty string, the last
> successfully executed regular expression is used instead."
>

Hello Bill,

Thanks for (en)lightning answer.
You saved a few hours of my frustration ;-)

Stanislaw Romanski
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