FreeBSD - Find updates for programs in jails

find_jail_updates.sh

# portmaster need to be installed in all jails

jls | grep -v JID | tr -s " " | cut -d' ' -f2 | xargs -I {} sh -c 'echo {} && jexec -U root {} portmaster -L | grep New | cut -d: -f2'

# jls                   #  list jails
# grep -v JID           #  get all lines without JID in it (-v is negation)
# tr -s " "             #  replace multiple newlines with one
# cut -d' ' -f2         #  split string on newlines and select part 2
# xargs -I {} sh -c ''  #  split string on newlines and spaces into argument list, then use {} as argument placeholder, then execute sh -c command
# sh -c ''              #  execute sub-shell with commands in string
# echo {}               #  output argument (placeholder = jailnumber)
# jexec -U root {} cmd  #  execute command in jail
# portmaster -L         #  get list of installed ports
# grep New              #  find lines with 'New' in it
# cut -d: -f2           #  split string on colon and select part 2