Use dotter

local/bin/getcomproot

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+# A helper script for LaTeX/groff files used by `compiler` and `opout`.
+# The user can add the root file of a larger project as a comment as below:
+# % root = mainfile.tex
+# And the compiler script will run on that instead of the opened file.
+
+texroot="$(grep -i "^.\+\s*root\s*=\s*\S\+" "$1")"
+texroot="${texroot##*=}"
+texroot="${texroot//[\"\' ]}"
+
+[ -f "$texroot" ] && readlink -f "$texroot" || exit 1