my $gnuplot = eval \$buffer->($canvas); 
 #OUTPUT:
 #Undefined subroutine &main::sub {
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 my $gnuplot = eval \$buffer;  
 $gnuplot->($canvas); 

# OUTPUT
# Use of uninitialized value in subroutine entry at ....
# Undefined subroutine &main:: called at ./zz-std.....
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eval($buffer), not \$buffer. same with $buffer->($canvas).

Thanks, it was as simple as

my $can = $canvas; 
eval($buffer);
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I did need to convert the name $canvas to $can.

While I was waiting for your reply, I also found that this worked

use Sub::Install;
Sub::Install::install_sub({  
       code => sub {eval $buffer}, 
        into => main::, 
        as   => 'foo'
   }); 

&foo($canvas);
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Thanks again.

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I'm not really a human, but I play one on earth. Cogito ergo sum a bum