We provide a format-string-like way of describing how to call particular tools. Thus the input is (1) a particular format string (2) a partial map from upper-case letters to strings; we call these strings the _insert_ strings. We map the format string to an output string in which combinations of the form %[upper-case-letter] in the format string are replaced by the corresponding insert string; if no such string exists this is an error.
We also provide a mechanism for escaping the insert strings. Specifically, there is a fixed partial map from lower-case letters to functions :: String -> String; these functions we call the transformers. For a combination of the form %[lower-case-letter-1]...[lower-case-letter-n][upper-case-letter] we take the insert string corresponding to upper-case-letter, and then pass it through the transformers corresponding to lower-case-letter-n, and so on down to the transformer corresponding to lower-case-letter-1.
Sections of the input string not containing % are left untouched.
Defined transformers with their corresponding letters: b transformer suitable for escaping bash strings quoted with . e transformer suitable for escaping emacs lisp strings quoted with . None of these transformers insert the closing or end quotes, allowing you to use them in the middle of strings.
Other transformers will be added as the need arises.