The post-weave, very much the après-ski experience of weaving, is a moment when Inweb can (if a pattern has told it to) perform some follow-on work with the documents it has just woven. As with the après-ski, by default nothing happens.

In fact, nothing will ever happen unless the pattern for a weave has a declaration containing a commands block. For example, the pattern PDFTeX is declared like so:

Pattern "PDFTeX" {
	based on: TeX
	initial extension: .tex
	commands
		if pdftex -output-directory=WOVENPATH -interaction=scrollmode WOVEN.tex >WOVEN.console; then echo "no pdftex errors"; else cat WOVEN.console; fi
		PROCESS WOVEN.log
	end
}

The conundrum here is this. PDFTeX wants to produce PDF documents. But Inweb can only produce TeX source code: for this to be turned into a PDF, it needs to be run through some external tools — not least some form of TeX. Inweb cannot contain those tools within itself, so it has to call out to the surrounding operating system's shell. This is what the commands do.

This feature might not seem worth it for a single file, but bear in mind that Inweb might be producing 200-odd files at a time, one for each section of a large web. It's much more convenient to have Inweb manage the process of turning all those individual TeX files into PDFs, not least because Inweb will get their fiddly filenames correct.

Each line of the commands block is a shell command, unless it has the form PROCESS filename. This gives Inweb the chance to look at the file if it wants to. That's in practice only ever going to be useful for TeX: what Inweb does is to scan through the output produced by TeX to see if there have been overfull hbox errors, count the number of pages, and such. So, really, it should be used only by the definition above, and in definitions of other TeX variants like it.

Here is the above post-weave system in action:

    $ inweb weave pyramid.c.md -as PDFTeX
    weaving web "Hilbert's Pyramid" (C program in MarkdownCode notation) as PDFTeX (based on TeX)
    (if pdftex -output-directory='.'  -interaction=scrollmode 'pyramid.tex'  >'pyramid.console'; then echo "no pdftex errors"; else cat pyramid.console; fi)
    no pdftex errors
        [pyramid.tex: 3pp 297K]

Note that WOVENPATH in one command has become . (the output directory happens to be the current working directory here), while each WOVEN has become pyramid. Note that WOVEN cannot begin with -, or contain any spaces, so that a command like rm WOVEN.log would not be quite the invitation to walk through a graveyard at night that it might seem. Those are the only two substitutions made by Inweb when it passes these commands to the system shell.