in reply to Constants refferences

The short answer is that ARRAY_REF is a reference and STRING is not.

What you put between ${} or @{} needs to be a reference. By itself, STRING is not a reference—it's just a string. To get a reference to that string, use the backslash. Hence: "${\STRING}". It's the same as "${\'.+?'}".

If you have a bareword between ${}, or a literal string, that's taken as the name of a variable ("${STRING}" is the same as "$STRING"). If you're using strict, then that's going to bomb (unless that variable's been declared somewhere).

ARRAY_REF is already a reference, so you don't have to backslash it. You do, however, have to keep "@{ARRAY_REF}" from being interpreted as "@ARRAY_REF", and so the "+" is there to mark it as an expression and not just a bareword.

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Re^2: Constants refferences
by gone2015 (Deacon) on Aug 21, 2008 at 17:28 UTC
    If you have a bareword between ${}, or a literal string, that's taken as the name of a variable ("${STRING}" is the same as "$STRING").

    It appears to be more complicated than that:

      use strict ; use warnings ;

  my $x = 57 ;
  print "\${x}   = '", ${x}, "'\n" ;
  print "\${'x'} = '", ${'x'}, "'\n" ;

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    gives: 
      ${x}   = '57'
  Can't use string ("x") as a SCALAR ref while "strict refs" in use ..
+.

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    Turning off "strict refs" gives: 
      ${x}   = '57'
  Use of uninitialized value in print ...
  ${'x'} = ''

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    Replacing my $x by our $x, gives: 
      ${x}   = '57'
  ${'x'} = '57'

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    The interpretation of the bareword case doesn't look desperately useful to me... Anybody know why Perl doesn't treat it as a subroutine/constant ?

    Sadly, this wouldn't help "${CONSTANT}" but it would mean that @{REF_ARRAY_CONSTANT} would do what might be expected.

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[d/l]
[select]
      Ambiguous use of ${x} resolved to $x at - line 4.
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