Re: How to set relational operators to variables to be used by program

I just skimmed through your code and then the question at the end. It seems you wish to avail the "dynamic operator" functionality.
Please check if the following code serves your purpose.

$num1=10;
$num2=20;
for $op ("<",">","==")
{
        if(eval "$num1 $op $num2")
        {
            print "\n$num1 $op $num2 is TRUE";
        }
        else
        {
            print "\n$num1 $op $num2 is FALSE";
        }
}

#---------------OUTPUT-----------
10 < 20 is TRUE
10 > 20 is FALSE
10 == 20 is FALSE
[download]

Comment on Re: How to set relational operators to variables to be used by program Download Code

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Re^2: How to set relational operators to variables to be used by program by dkhalfe (Acolyte) on Jul 19, 2012 at 16:27 UTC
`for my $op ($filter [0]->[1]) { if (eval "$hash{$filter[0]->[0]} $op $filter[0 +]->[2]") { print OUTFILE $line, "\n"; } }` [download] This seems to work. Thanks! If any one else has other suggestions please inform!	[reply] [d/l]
Re^3: How to set relational operators to variables to be used by program by jethro (Monsignor) on Jul 19, 2012 at 17:27 UTC
The usual warning: If you use eval, you have to make sure that either no evildoer can put any code into the file where the opcodes are stored or that you check the values with regexes so that only acceptable ops get through And something else: If you use `$hash{$filter[0]->[0]}` inside the eval string, it is substituted with its value as well. This is fine as long as you want to compare numbers, because (10 < 20) is a valid comparision expression in perl, but if you want to also compare strings, for example "blue" and "green", then the eval will fail because (blue lt green) is not a valid expression, it should be ("blue" lt "green"). Solution: Escape the operands like this: `\$hash{\$filter[0]->[0]}` And your example filter 3 (for column b) is wrong, '=' is assignement, '==' is equality (which would suggest that a regex to check for correct relationships/operators might not be a bad idea anyway)	[reply] [d/l] [select]
Re^4: How to set relational operators to variables to be used by program by dkhalfe (Acolyte) on Jul 19, 2012 at 18:04 UTC
How would I go about checking the vlaues with regexes?	[reply]
Re^5: How to set relational operators to variables to be used by program by jethro (Monsignor) on Jul 23, 2012 at 12:23 UTC
Re^3: How to set relational operators to variables to be used by program by cheekuperl (Monk) on Jul 19, 2012 at 16:31 UTC
For that matter, you can also write: `if (eval "$hash{$filter[0]->[0]} $filter [0]->[1] $filter[0]->[2]") { print OUTFILE $line, "\n"; }` [download] eliminating the extra for loop.	[reply] [d/l]