3.5.4 `extract' - extract text from another file

Usage: (extract file-name marker-fmt [ caveat ] [ default ])
This function is used to help construct output files that may contain text that is carried from one version of the output to the next.

The first two arguments are required, the second are optional:

• The file-name argument is used to name the file that contains the demarcated text.
• The marker-fmt is a formatting string that is used to construct the starting and ending demarcation strings. The sprintf function is given the marker-fmt with two arguments. The first is either "START" or "END". The second is either "DO NOT CHANGE THIS COMMENT" or the optional caveat argument.
• caveat is presumed to be absent if it is the empty string (""). If absent, "DO NOT CHANGE THIS COMMENT" is used as the second string argument to the marker-fmt.
• When a default argument is supplied and no pre-existing text is found, then this text will be inserted between the START and END markers.

[+ (extract "fname" "// %s - SOMETHING - %s" ""
"example default") +]

// START - SOMETHING - DO NOT CHANGE THIS COMMENT
example default
// END   - SOMETHING - DO NOT CHANGE THIS COMMENT

NOTE:

You can set aside previously generated source files inside the pseudo macro with a Guile/scheme function, extract the text you want to keep with this extract function. Just remember you should delete it at the end, too. Here is an example from my Finite State Machine generator:

[+ AutoGen5 Template  -*- Mode: text -*-
h=%s-fsm.h   c=%s-fsm.c
(shellf
"[ -f %1$s-fsm.h ] && mv -f %1$s-fsm.h .fsm.head
[ -f %1$s-fsm.c ] && mv -f %1$s-fsm.c .fsm.code" (base-name)) +]

This code will move the two previously produced output files to files named ".fsm.head" and ".fsm.code". At the end of the 'c' output processing, I delete them.

Arguments:
file-name - name of file with text
marker-fmt - format for marker text
caveat - Optional - warn about changing marker
default - Optional - default initial text