Bash – Two commands, one pipeline

Why not just do:

{ echo foo; echo bar;} > /tmp/p

If you want your controlling script to leave the pipe open, you can do:

exec 3<> /tmp/p

Opening a named pipe in read-write mode is to avoid that to block if the pipe hasn't been opened yet. That would instantiate it if it wasn't yet. It works on Linux at least but is not guaranteed to by POSIX.

Alternatively (and portably):

: < /tmp/p & exec 3> /tmp/p

Then instead of having each process open the named pipe, you can also do:

cmd >&3

And in the end, you'd do:

exec 3>&-

To close the writing end to let readers know it's finished.

change all <s to >s and <s to >s if you need the logic to be the other way round.

If you want to see the nameservers listed by the registrar, those are available in the DNS system via the root servers.

For example:

 dig @a.gtld-servers.net ns stackoverflow.com

; <<>> DiG 9.10.2-P4 <<>> @a.gtld-servers.net ns stackoverflow.com
; (2 servers found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55658
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 3
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;stackoverflow.com.     IN  NS

;; AUTHORITY SECTION:
stackoverflow.com.  172800  IN  NS  cf-dns02.stackoverflow.com.
stackoverflow.com.  172800  IN  NS  cf-dns01.stackoverflow.com.

;; ADDITIONAL SECTION:
cf-dns02.stackoverflow.com. 172800 IN   A   173.245.59.4
cf-dns01.stackoverflow.com. 172800 IN   A   173.245.58.53

;; Query time: 65 msec
;; SERVER: 192.5.6.30#53(192.5.6.30)
;; WHEN: Mon Sep 21 15:53:29 GMT 2015
;; MSG SIZE  rcvd: 124

If you modify the name servers listed in your registrar account, those servers will be reflected in the root / gtld servers. When you modify your DNS zones that your nameservers serve, they have no effect on the results returned by the root servers. Additionally, the only records the root servers will return are NS and A/AAAA defined by the registrar for the listed NS records. These are just pointers to find the authoritative (per the registrar) name servers for a domain to send your queries to.