Created SC2229 (markdown)

SC2229.md

@@ -0,0 +1,39 @@
+## This does not read 'foo'. Remove $/${} for that, or use ${var?} to quiet.
+
+### Problematic code:
+
+```sh
+read $foo
+```
+
+### Correct code:
+
+```sh
+read foo
+```
+
+### Rationale:
+
+`read` takes a variable name, but shellcheck has noticed that you give it an expanded variable instead. This will populate whatever the variable expans to instead of the variable itself. For example:
+
+    foo=bar
+    read $foo   # Reads data into 'bar', not into 'foo'
+    read foo    # Reads data into 'foo'
+
+### Exceptions:
+
+If this is intentional and you do want to read a variable through an indirect reference, you can silence this warning with a directive:
+
+```sh
+# shellcheck disable=SC2229
+read "$foo"
+```
+
+Or take advantage of the fact that ShellCheck only warns when no parameter expansion modifiers are applied:
+
+```sh
+read "${foo}"    # ShellCheck warns
+read "${foo?}"   # No warning
+```
+
+`${foo?}` fails when `foo` is unset, which is fine since `read` would have failed too. The main side effect is an improved runtime error message in that case.