Most likely, you have read in line-ending characters when you read the PERSON file.

ldap probably cannot find the person, and returns an empty $dn.

Fix by: 

while (<PERSON>) {
   chomp; # Strip trailing line-ending
   #.. process ldap stuff

[download]
Your query would look much prettier, and be easier to answer if you followed Writeup Formatting Tips, and used code tags.

Update: Fixed typo, and adding this recommendation:
Use the 3-parameter doem of OPEN: 

  open PERSON, "<", "ou3" or die "Cannot open 'ou3': $!";

[download]

     Syntactic sugar causes cancer of the semicolon.        --Alan Perlis

In reply to Re: Perl Builds an LDIF by NetWallah
in thread Perl Builds an LDIF by rfransix

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