How to use an expression in the replacement side of the perl substitution operator?

I'm pretty new to perl and facing one issue. This might sound as a silly question but I want to understand it well.

So I've a string variable containing a substring which I want to replace with a string of hashes.

my $l_filedata = 'abcOVERRIDE_CONTAINS_FUNCTIONSasdfghjk';

and

my $hash_ref = {};
Dumper($hash_ref->{'ContainsMessage'}); # This returns a hash and I've maintained it under scalar variable

Output
------
{
  '23.2.10103' => 1,
  '23.2.10101' => 1,
  '23.2.10102' => 1
}

So I want to perform a find-replace operation and the way I'm doing it is

$l_filedata =~ s/OVERRIDE_CONTAINS_FUNCTIONS/eval(Dumper($hash_ref->{'ContainsMessage'}))/g;

I'm trying to convert the hash to a string using Dumper and then want to replace the string with that Dumper-returned string. But it's always returning me abceval(Dumper(HASH(0xe88f00)))asdfghjk. I think the replacement expression is getting treated as string not an expression.

When I do it like this -

my $temp = Dumper($hash_ref->{'ContainsMessage'});
$l_filedata =~ s/OVERRIDE_CONTAINS_FUNCTIONS/$temp/g;

It's working as expected. Can someone tell me what am I missing here?

Solution

Use the e flag to treat the replacement part as code to evaluate rather than the body of string literal.

s/OVERRIDE_CONTAINS_FUNCTIONS/ Dumper( $hash_ref->{ ContainsMessage } ) /eg

But do you really want to dump the structure multiple times? The following (which you already mentioned) is probably the way to go:

my $replacement = Dumper( $hash_ref->{ ContainsMessage } );

s/OVERRIDE_CONTAINS_FUNCTIONS/$replacement/g

s{...}{...}

is equivalent to

s{...}{ qq{...} }e

This means that

s{...}{eval(Dumper(...))}

is equivalent to

s{...}{ qq{eval(Dumper(...))} }e

But you simply want

s{...}{ Dumper(...) }e