how to write a patten that matches till the end of first \n

I have a string as shown below.

"CPU_DEF = NAND_ONLY \nI2C_DEF = I2C_CTRL \nPCL = TARGET\n"

Here I2C_CTRL is assigned to I2C_DEF. I want to match anything that is assigned to I2C_DEF, including \n should match. But PCL = TARGET\n should not be matched. How to write regular expresion for this?