If you are dealing with six thousand lines, of about this size, and know that it will never become larger, then you can probably be quite brute-force about your approach and it will work just fine. Read the lines from file #1 into an array, then use, say, the grep() function to search for a regular expression such as ^$hostname\: ... thus looking for “starting at the beginning of the line, look for $hostname followed by a colon-character.” Use split() to split-up the lines as needed. There are several equally-good ways to do this.
Also consider the possibility of using Unix command-line tools such as grep, egrep, sort, merge, and especially diff. Sometimes, you discover that you don’t have to “write a program” at all!
While we don’t offer a program-writing service or homework-service, it certainly is possible to “try sincerely to write it” and then to ask us for specific help.