An extremely influential paper by RobPike, then at BellLabs.
The current UNIX® text processing tools are weakened by the built-in concept of a
line. There is a simple notation that can describe the ‘shape’ of files when the typical
array-of-lines picture is inadequate. That notation is regular expressions. Using regular
expressions to describe the structure in addition to the contents of files has interesting
applications, and yields elegant methods for dealing with some problems the current tools
handle clumsily. When operations using these expressions are composed, the result is
reminiscent of shell pipelines.
Rob Pike, "Structural Regular Expressions", EUUG Spring 1987 Conference Proceedings , Helsinki, May 1987