Created SC2006 (markdown)

SC2006.md

@@ -0,0 +1,23 @@
+# Use $(..) instead of deprecated `..`
+
+### Problematic code:
+
+    echo "Current time: `date`"
+
+### Correct code:
+
+    echo "Current time: $(date)"
+
+### Rationale:
+
+Backtick command substitution `` `..` `` is legacy syntax with several problems.
+
+1. It has a series of undefined behaviors related to quoting in POSIX.
+1. It imposes a custom escaping mode with surprising results.
+1. It's exceptionally hard to nest. 
+
+`$(..)` command substitution has none of these problems, and is therefore strongly encouraged.
+
+### Contraindications
+
+None.