$test="\$\{This\$\{One\}and\$\{also\}this\}";


$test=~/\$\{(([^\{\$\}]*(?:\$\{[^\$\{\}]+\}[^\$\{\}]*)*))\}/gxs;

print "test:$1";
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Try this.I haven't made any changes in your regexp i just added two brackets to get the required values($1)