If the data format is consistent in terms of always having at least one blank line between consecutive records, and never having a blank line within a record, then you can set the INPUT_RECORD_SEPARATOR to read one whole record at a time into $_, and this can simplify things a lot: 
{
  local $/ = ""; # set to empty string -- see perldoc perlvar

  while (<>) {
     if ( /(\ncn: (\S+))\n(\S+)/ ) {
        my ( $cnline, $cnval, $nexttag ) = ( $1, $2, $3 );
        if ( $nexttag ne "uid" ) {
           s/$cnline/$cnline\nuid: $cnval/;
        }
     } else {
        warn "Record $. has no cn value\n";
     }
     print;
  }
}

[download]
(not tested)

In reply to Re: Perl File Manipulation by graff
in thread Perl File Manipulation by topperge

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