If you want to have a way to specify rules that use the same command, but still specify the rules manually, look up "!macros" in `man tup`. If the issue is that the commands need to write and read some temp files, then note that you can write temp files in a tup command (they need to be placed in $TMPDIR iirc). Note that the tup command can be calling a script that you place alongside, in case this makes specifying your sequences of commands easier. You can define the macro in top-level Tuprules.tup and use include_rules in all the Tupfiles to get it included.
Thanks, the `!macro` thing seems to be what I was looking for. Having intermediary temporary files is of course fine.
The use-case at that time was to convert a LaTeX file containing a TIKZ image (therefore having a .tikz file extension) to an SVG which required compiling the LaTeX code to PDF, cropping the PDF and converting it to SVG. Since there were multiple occurrences of this across the project, I wanted to have that as a reusable "function" in the build system. I did not want to write a dedicated script for this because of portability issues (Shell vs. Batch).
How does !macro rid you of that portability issue? One way or another, you'd need to have a command that does that whole sequence of operations. If it's inline, I'd expect same portability problem (`&&` in Bash corresponds to something else in `.bat`).
What you could do is use Tup's LUA support (you can write tupfiles and tuprules in LUA, and you can define and use LUA functions in them): have each rule handle just one step of your process, generate the whole necessary DAG of rules, encapsulate all of that in a LUA function defined in tuprules.lua and call that function in tupfile.lua for every diagram you want to generate. One thing that you lose is the ability to use `foreach` with your construction (other than by creating a variant of your constructions that embeds foreachness, or by using tup.glob and iterating).
Does this fail to address your problem?