in reply to Variables in extended patterns?

You can use variables inside 'extended' patterns, but if you use 'extended' patterns, unescaped whitespace will be ignored. So, Perl happily interpolates a carriage return and a linefeed, and then, when it compiles and takes notice of the /x, it'll ignore them.

Considering that 

    s{$CR?$LF}

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doesn't contain any literal whitespace, the use of /x isn't quite needed. Furthermore, since you don't have a dot, there's no need for /s. And the absence of ^ and $ anchors make the /m superfluous as well.

Now, if you have a modern Perl (say, one released last year, like 5.10), you could write: 

    s/\R/\n/g;

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instead.

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Re^2: Variables in extended patterns?
by flamewise (Initiate) on Nov 05, 2008 at 16:19 UTC
    Thanks.

    I missed that whitespace will be discarded after variable imterpolation.

    About just omitting xms: Of course that's exactly what I did, never mind what some clever guy calls "best practises".

    I'm now trying to find documentation on what, exactly, \R does... My perl 5.8.6 lists a few escape-sequences in "man perlop", section "quote and quote-like characters", but not \R.

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      I said a modern perl. 5.8.6 is four years old. It doesn't have \R. 5.10 does. See 'man perlrebackslash' (yes, you need 5.10 for that as well)
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      You can always write 
      my $CRE = '0D';
my $LFE = '0A';
s{\x{$CRE}?\x{$LFE}}{\n}xms;
s{\015?\012}{\n}xms;
s{\x0D\x0A}{\n}xms;

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      or 
      
my $CRE = '\x0D';
my $LFE = '\x0A';

$_ = qq,aod \x0D\x0A another \x0D\x0A no more,;

s/$CRE?$LFE/--/msxg;
print;
__END__
aod -- another -- no more

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