The old code used a shell loop to convert each controlling macro
definition into a command-line argument, reading the macro definitions
file each time. The new code converts the list of controlling macros
into a sed script which can run through the list of macro definitions
in one go.
Add some explanatory comments, since the code is quite meta.
Use {} instead of () for redirecting a group of commands.
Submitted by: Jonathan Nieder <jrnieder@gmail.com>
84a3c48bb4