Before, sed would add quotes to every line of the single multiline argument,
causing the final quoted argument to "split ... command" or screen to contain
unquoted newlines such as this (from kakoune-cr):
tell application "iTerm"
tell current session of current window
tell (split vertically with same profile command "env PATH='...' 'sh' '-c' ''
' export KAKOUNE_SESSION=$1'
' export KAKOUNE_CLIENT=$2'
' shift 3'
''
' [ $# = 0 ] && set \"$SHELL\"'
''
' \"sh\"'
' ' '--' '51909' 'client0' 'terminal' ") to select
end tell
end tell
Instead of using sed to do this which operates on single lines at a time, simply
use printf to insert ' quotes before and after the entire argument.