Created SC2189 (markdown)

SC2189.md

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+## You can't have | between this redirection and the command it should apply to.
+
+### Problematic code:
+
+```sh
+< file.txt | grep foo
+```
+
+### Correct code:
+
+```sh
+< file.txt grep foo   # or more canonically: grep foo < file.txt
+```
+
+### Rationale:
+
+ShellCheck has found a stage in a pipeline that consists of a redirection but no command. This doesn't make sense because a redirection without a command will not read or write any data.
+
+This is most likely to occur when deleting a command that had a redirection, but leaving a `|` behind instead of moving the redirection to a different command:
+
+```
+# Match lines with line numbers
+nl < foo.txt | grep bar
+
+# Incorrect attempt at removing line numbers. grep now has no input:
+< foo.txt | grep bar
+
+# Line numbers correctly removed. grep now reads foo.txt as intended.
+grep bar < foo.txt
+```
+
+### Exceptions:
+
+It's technically valid to do e.g. `echo foo | > "$(cat)"` to truncate a file called "foo", but please consider rewriting such code.