esharris has asked for the wisdom of the Perl Monks concerning the following question:

Why does this program ... 
#!/usr/bin/perl -w

use strict;

my $x = 'Dwayne Johnson';

print <<XXX;
$x's the Rock.
XXX

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produce this output in perl, v5.8.1? 
Name "x::s" used only once: possible typo at ./test.pl line 7.
Use of uninitialized value in concatenation (.) or string at ./test.pl
+ line 7.
 the Rock.

[download]
The problems go away if I prepend the single quote with a backslash.

Replies are listed 'Best First'.
Re: <<, variable, and single quote behaving badly.
by saintmike (Vicar) on Apr 26, 2004 at 17:38 UTC
    $x's is a deprecated way of writing $x::s, a relict from Perl 4 days.
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Re: <<, variable, and single quote behaving badly.
by bart (Canon) on Apr 26, 2004 at 19:15 UTC
    Simply put: $x::s and $x's are equivalent to perl. The reason for that is backward compatibility: the apostrophe was perl4's package name separator, on perl5, it's the double semicolon. But the apostrophe still works.

    Sample code: 

      $Foo'x = 123;
  print $Foo::x;

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    Result: 
      123

    The odd thing might be that this still doesn't produce a warning under perl5.8.3.

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      For better or worse (better I suppose), this syntax will disappear in Perl 6 according to Apocalypse 2. See Larry's comments under RFC 071. Of course, large parts of A02 have been rethought since then, but I don't think this is one of them.
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Re: <<, variable, and single quote behaving badly.
by Plankton (Vicar) on Apr 26, 2004 at 17:34 UTC 
    $ cat monk.pl 
#!/usr/bin/perl -w

use strict;

my $x = 'Dwayne Johnson';

print <<XXX;
${x}'s the Sock.
XXX

$ ./monk.pl 
Dwayne Johnson's the Sock.

    [download]
    Think about it ... say if you wanted to say:
    Dwayne Johnson_s the Sock.
    Would you say ... 
    print <<XXX;
$x_s the Sock.
XXX

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    ... now is $x_s a variable or not? {} and \ tell << that x is a variable.

    Plankton: 1% Evil, 99% Hot Gas.
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