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Scalar input / convert to operator

Posted on 2000-04-16
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Last Modified: 2010-03-05

I have three arguments on the command line. One of which is a mathematical operator, such as +. I'm parsing the arguments to three scalars. How can I use the scalar as an math operator?
IE: $result = ($operand $operator $operand) ?  $result = ($operand + $operand).  Thanks!
davidt@t-online.de
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Question by:kenai
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azawawi earned 50 total points
ID: 2720477
if( $operator eq "+" ) {
  .....
} else if( $operator eq "-" ) {
}

i sense that what you're asking is not available in a language like Perl but is found in functional languages such LISP (you could construct a list and since every list is actually a statement of the form (operator operand1 operand2 ... operandN) you could execute it....

I dont think this is available in Perl....

Hope this helps....
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Expert Comment

by:adam923
ID: 2720833
it could be done as an eval but it's much easier and safer just to make a separate case for each operator, as azawawi shows above
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Expert Comment

by:azawawi
ID: 2721669
playing with lists & functions is a game than LISP (and its dialects) do well....
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Expert Comment

by:ozo
ID: 2721703
#you could do
$result = eval "$operand $operator $operand";
#but that could be dangerous if you allow someone to set something like
$operator = ',system("delete *.*"),'

#it may be safer to use  something like
$result = &{${{
'+' => sub {$_[0] + $_[1]},
'-' => sub {$_[0] - $_[1]},
'*' => sub {$_[0] * $_[1]},
'/' => sub {$_[0] / $_[1]},
}}{$operand}||sub{undef}}($operand,$operand);
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