Thank you for your answers, unfortunately after many tests, the LDAP filter does not use the value contained in the variable.

I put you the code that I currently use to see if you have another solution :

package cnmodule;

sub function1 {

use strict;
use Net::LDAP;

my ($local) = @_;
my $valueA;

my $ldap = Net::LDAP->new('ad.network',version => 3) 
   or die "Can t connect to LDAP ($@)";

  $valueA = $ldap->bind ("cn=usercheck,cn=users,dc=domain,dc=network",
+ password => 'password'); 
  $valueA->code && die $valueA->error;

  $valueA= $ldap->search(
   base => 'dc=domain,dc=network',
   scope => 'sub',
   filter => qq{(sn=q{$local})}, 
  );

$ldap->unbind();

  $valueA->code && die $valueA->error;
  foreach my $entry ($valueA->all_entries) {
     my $valueB = $entry->get_value('CN'); 
}
  return $valueB;
}

$variableA='test';
$variableB=function1($variableA);
print $variableB;
1;
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