Now I have an idea what you want.
The ^ must be at the beginning of the RE in order to mark the beginning of the line.
I see you have a multi-line block captured in a variable (that is, sigh, certainly not the best idea in shell).
A RE (here, ERE) is not made for multi-line and embedded newline characters. Nevertheless you can try if a literal newline works:
regex_needle=".*
$space\); *
"
Or with a nl variable:
nl=$'\n'
regex_needle=".*${nl}$space\); *${nl}"