In Perl, I need to read a .conf file that contains condition like $a>$b based on the result of the condition i have to execute either if or else block

Question

The content of condition.conf:

condition1=$a>$b

Example Perl code:

$cnd_ConfFile = $ARGV[0];
open(CONDITIONS, '<', $cndConfFile);

$cndCount=0;
while ( <CONDITIONS> ) {
        chomp; # no newline
        s/#.*//; # no comments
        s/^\s+//; # no leading white
        s/\s+$//; # no trailing white
        next unless length;
        ($var, $value) = split(/\s*=\s*/, $_, 2);
        $cndOnCounterValues[$cndCount++]=$value;
}

close CONDITIONS;

$cond = $cndOnCounterValues[0];
print "\n$cond\n";

$a=3;
$b=5;

if($cond){
  print "a is greater then b";
}
else
{
  print "b is greater then a";
}

The above code always gives the output "a is greater then b".

Regardless of the values of $a and $b.

Answer 1

I assume that you want to eval the $a>$b expression that literally appears in your config file. To do that replace:

if ($cond) {

with:

if (eval $cond) {

That should to the trick.

Disclaimer: don't do this unless you know what you are doing (see comments).

Answer 2

Here i a quick example that seems to satisfy your problem.

#! /usr/bin/env perl
use strict;
use warnings;

my @cond;
{
  while( <> ){
    chomp;
    next unless length;
    next if m' ^ \s* \# 'x;

    next unless m' (\w+) \s* = \s* (.*?) \s* $'x;
    push @cond, [$1,$2];
  }
}
my($a,$b);

$a=3;
$b=5;

for my $elem ( @cond ){
  my($name,$cond) = @$elem;

  if( eval $cond ){
    print "$name is true, because $cond matches "
  }else{
    print "$name is false, because $cond doesn't match "
  }
  print '(', eval("qq{$cond}"), ")\n";
}

echo 'condition1=$a>$b
condition2=$a<$b' | perl test.pl

condition1 is false, because $a>$b doesn't match (3>5)
condition2 is true, because $a<$b matches (3<5)