mkdir "$tmpdir"
+# 'guix environment' launches /bin/sh if 'SHELL' is unset, so export 'SHELL'
+# since we know it's valid (build environments lack /bin/sh.)
+export SHELL
+
# Check the environment variables for the bootstrap Guile.
guix environment --ad-hoc guile-bootstrap --pure --search-paths > "$tmpdir/a"
guix environment --ad-hoc guile-bootstrap:out --pure --search-paths > "$tmpdir/b"