See https://github.com/koalaman/shellcheck/pull/2625

SC3061.md

@@ -0,0 +1,29 @@
+## `read` without a variable is undefined.
+
+### Problematic code:
+
+```sh
+while read -r;
+do
+    echo "line: ${REPLY}"
+done < foolist
+```
+
+### Correct code:
+
+Add a variable to read and use it later on:
+
+```sh
+while read -r foo;
+do
+    echo "line: ${foo}"
+done < foolist
+```
+
+### Rationale:
+
+This behavior is not allowed [in POSIX](https://pubs.opengroup.org/onlinepubs/9699919799/utilities/read.html).
+
+### Exceptions:
+
+None. This warning is not emitted in `ksh` or `bash` where read can be used without an argument.