add xz-to-gz script

- converts .xz files to .gz recursively

- graphdb wants .gz files; so there we go

ulo/xz-to-gz.sh

+#! /bin/sh
+
+# given a path, traverse that file system tree and extract all
+# .xz files and re-compress them to .gz; some tooling, in particular
+# graphdb, only supports gz and not xz
+
+set -eu
+
+if [ ! $# -eq 1 ]; then
+    echo "usage: $0 DIRECTORY" 1>&2
+    exit 1
+fi
+
+directory="$1"
+files=$(find "$directory" -name "*.xz")
+
+for file in $files; do
+    echo "$file" 1>&2
+
+    # the filename of the extracted (uncompressed) file
+    rdf_file=$(echo "$file" | sed 's/\.xz//')
+
+    # uncompress and then compress again
+    unxz "$file"
+    gzip "$rdf_file"
+done