Footnotes

(1)

GNU Autoconf, Automake and Libtool, by G. V. Vaughan, B. Elliston, T. Tromey, and I. L. Taylor. SAMS (originally New Riders), 2000, ISBN 1578701902.

(2)

Because M4 is not aware of Sh code, especially conditionals, some optimizations that look nice statically may produce incorrect results at runtime.

(3)

Using defn.

(4)

Yet another great name from Lars J. Aas.

(5)

Note that GNU make has heuristics to avoid spawning a shell at all if the command is deemed safe to be executed directly.