Perl regex strange behaviour - regex

Question

Method 1:
$C_HOME = "$ENV{EO_HOME}\\common\\";
print $C_HOME;
gives C:\work\System11R1\common\
ie The environment variable is getting expanded.
Method 2:
Parse properties file having
C_HOME = $ENV{EO_HOME}\common\
while(<IN>) {
if(m/(.*)\s+=\s+(.*)/)
{
$o{$1}=$2;
}
}
$C_HOME = $o{"C_HOME"};
print $C_HOME;
This gives a output of $ENV{EO_HOME}\common\
ie The environment variable is not getting expanded.
How do I make sure that the environment variable gets expanded in the second case also.

Answer 1

The problem is in the line:
$o{$1}=$2;
Of course perl will not evaluate $2 automatically as it read it.
If you want, you can evaluate it manually:
$o{$1}=eval($2);
But you must be sure that it is ok from security point of view.

Answer 2

the value of $o{C_HOME} contains the literal string $ENV{C_HOME}\common\. To get the $ENV-value eval-ed, use eval...
$C_HOME = eval $o{"C_HOME"};
I leave it to you to find out why that will fail, however...

Answer 3

Expression must be evaluated:
$C_HOME = eval($o{"C_HOME"});

Answer 4

Perl expands variables in double-quote-like code strings, not in data.
You have to eval a string to explicity interpolate variables inside it, but doing so without checking what you are passing to eval is dangerous.
Instead, look for everything you may want to interpolate inside the string and eval those using a regex substitution with the /ee modifier.
This program looks for all references to elements of the %ENV hash in the config value and replaces them. You may want to add support for whitespace wherever Perl allows it ($ ENV { EO_HOME } compiles just fine). It also assigns test values for %ENV which you will need to remove.
use strict;
use warnings;
my %data;
%ENV = ( EO_HOME => 'C:\work\System11R1' );
while (<DATA>) {
if ( my ($key, $val) = m/ (.*) \s+ = \s* (.*) /x ) {
$val =~ s/ ( \$ENV \{ \w+ \} ) / $1 /gxee;
$data{$key} = $val;
}
}
print $data{C_HOME};
__DATA__
C_HOME = $ENV{EO_HOME}\common\
output
C:\work\System11R1\common\