LdifParser is a simple class to parse ldif file

require 'ldif_parser'

ldif_path = '/tmp/ldap.bak'
LdifParser.open(ldif_path, only: %w[displayName givenName sn mail]).each do |entry|
  p entry
end

$ gem install ldif_parser

Use each method to iterate on each ldif entries and do what you want.

If the ldif file is too large, you can optimize the processing of the file with the only and except options.

These options allow you to limit the number of lines in the ldif file that will be parsed.

• minimized: minimize has string all array with only one value
• only: captures only the specified ldap attributes
• except: ignore the specified ldap attributes

$ time ruby test/speed.rb 
ruby -v => 3.1.6p260
wc -l $path => 1000000

real    0m4,562s
user    0m4,457s
sys     0m0,091s