How to match everything up to the second occurrence of a character?

This will capture up to but not including the second comma:

[^,]*,[^,]*

English translation:

• [^,]* = as many non-comma characters as possible

• , = a comma

• [^,]* = as many non-comma characters as possible

[...] is a character class. [abc] means “a or b or c”, and [^abc] means anything but a or b or c.