Small php function

I need a function to search for a certain string with content inside of it, and replace the entire sting with something else.

For example: text text BC=32A2234 text text text.

Then the entire "BC=32A2234" should be replaced with something. The length after the part "BC=" might vary. There might also be more than one occurance per string.

The function should be something like:
bc_search($string), where $string is input text.

The function should be used like:
$replacement_string = bc_search($string);

I can write the part where the occurance is replaced myself. You must store the part after "BC=" in a variable inside of the function, so its easy for me to do that part.

Code needs to be commented in english and easily understandable.