The code snippet you sent me does exactly what I wanted. Assuming your permission, I'm posting it here for all to see.

 if ( eval { require Clone; Clone::clone( "testdata" ); 1 } ) {
    eval "use Clone qw( clone );"
  } else {
    eval "use Clone::PP qw( clone );"
  }
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Thanks to all and particularly to simonm for their help! This has indeed been a warm welcome to perlmonks.