我正在尝试匹配和替换字符串的形式
mystring = "string-text"
与
mystring = "XYZ string-text"

• 当且仅当 * string-text不等于red时。例如

original-text             replacement
-------------             -----------
mystring = "red"          mystring = "red"
mystring = "green"        mystring = "XYZ green"
mystring = "blue"         mystring = "XYZ blue"
mystring = "reds"         mystring = "XYZ reds"
mystring = "_red"         mystring = "XYZ _red"
mystring = "1ed"          mystring = "XYZ 1ed"
mystring = "ree"          mystring = "XYZ ree"
mystring = ""             mystring = "XYZ "
mystring = "12345678"     mystring = "XYZ 12345678"

mystring = "red"保持不变，所有其他的都按照描述替换。是否存在一个正则表达式来实现这一点？
我能想到的最好办法就是

^mystring = "(?!red)(.*)"$

捕获组(.*)允许使用mystring = "XYZ \1"打印替换。这在大多数情况下有效，但在测试用例mystring = "reds"中失败