If you use Back To My Mac on your Mac, then you are assigned a unique domain name such as "987654321.members.btmm.icloud.com." That domain is only usable on other Macs which are connected to the same iCloud account. In order to find your BTMM domain, you can use the following commands:

btmm.sh

  # On the command line (note the single \ before the $NF)

echo show Setup:/Network/BackToMyMac | scutil | awk -F' ' "/$UID/{print \$NF}"

alias btmm='echo show Setup:/Network/BackToMyMac | scutil | awk -F" " "/$UID/{print \$NF}"'

function btmm { echo show Setup:/Network/BackToMyMac | scutil | awk -F" " "/$UID/{print \$NF}" }

BTMM=$(echo show Setup:/Network/BackToMyMac | scutil | awk -F' ' "/$UID/{print \$NF}")

  # However, if you want to assign it to a variable using FOO=`bar` syntax, then you must use two backslashes:

BTMM=`echo show Setup:/Network/BackToMyMac | scutil | awk -F' ' "/$UID/{print \\$NF}"`

Previously I had been using this to get my Back To My Mac domain:

echo show Setup:/Network/BackToMyMac | scutil | sed -n 's/.* : *\(.*\).$/\1/p'

however, that does not work if there is more than one user with an iCloud/BackToMyMac account on the same Mac.

(I did not come up with that original command, but unfortunately I cannot find the original source for it anymore.)