"APL influenced the development of pipes. APL did not allow the use of operators with variants, which many utilities had at the time. It only took a willingness to throw in a new separator, the vertical bar. About four years passed, from the time they started talking about developing a new separator, to the time it happened."
Ken Thompson wrote an APL interpreter for early Research UNIX.
source: http://www.cs.dartmouth.edu/~doug/reader.pdf
McIlroy:
"APL influenced the development of pipes. APL did not allow the use of operators with variants, which many utilities had at the time. It only took a willingness to throw in a new separator, the vertical bar. About four years passed, from the time they started talking about developing a new separator, to the time it happened."
source: https://www.princeton.edu/~hos/frs122/precis/mcilroy.htm