The original Bourne shell, the ancestor to the Bourne-Again Shell (bash) was written in C.

Well, almost.

The original Bourne shell was written in a highly modified version of C (#define anyone?). Bourne called it “Bournegol” and it converts many of C’s structure to Algol-style structure.

#define IF      if(
#define THEN    ){
#define ELSE    } else {
#define ELIF    } else if (
#define FI      ;}

All of the #defines used can be found here.