The code example above was meant as a counter-example to what I understood LanX to be saying. Comments:

my %hash = ('$1' => 'oops',  'abc' => 'ok');  # create a hash

'abc' =~ m{ (abc) }xms;   # capture a sub-string to $1
print qq{captured '$1'};  # show what that string is

print $hash{'$1'};  # show effect of single-quotes: no interpolation
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Had  $1 been used directly (as in $hash{ $1 }), the output would have been 'ok'. A more complete example:

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my %hash = ('$1' => 'oops',  'abc' => 'ok');
 dd \%hash;
 ;;
 'abc' =~ m{ (abc) }xms;
 print qq{captured '$1'};
 ;;
 print 'single-quoted: ', $hash{'$1'};
 print 'straight: ', $hash{ $1 };
"
{ "\$1" => "oops", "abc" => "ok" }

captured 'abc'
single-quoted: oops
straight: ok
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