Created SC2050 (markdown)

SC2050.md

@@ -0,0 +1,33 @@
+## This expression is constant. Did you forget the `$` on a variable?
+### Problematic code:
+
+```sh
+if [ myvar = "test" ]
+then
+  echo "Test mode"
+fi
+```
+
+### Correct code:
+
+```sh
+if [ "$myvar" = "test" ]
+then
+  echo "Test mode"
+fi
+```
+### Rationale:
+
+ShellCheck has found a `[ .. ]` or `[[ .. ]]` comparison that only involves literal strings. The intention was probably to check a variable or command output instead.
+
+This is usually due to missing `$` or bad quoting:
+
+    if [[ "myvar" = "test" ]]             # always false because myvar is a literal string
+    if [[ "$myvar" = "test" ]]            # correctly compares a variable
+
+    if [ 'grep -c foo bar' -ge 10 ]       # always false because grep doesn't run
+    if [ "$(grep -c foo bar)" -ge 10 ]    # correctly checks grep output
+
+### Exceptions:
+
+None