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+## (..) is a subshell. Did you mean [ .. ], a test expression?
+
+### Problematic code:
+
+```sh
+if ( 1 -lt 2 )
+then
+  echo "1 is less than 2"
+fi
+```
+
+### Correct code:
+
+```sh
+if [ 1 -lt 2 ]
+then
+  echo "1 is less than 2"
+fi
+```
+### Rationale:
+
+Tests like `-eq` to check numeric equality or `\<` for string comparison only work are actually parameters to the `test` command, and only work as tests in that context. `[` is an alias for `test`, so you'll frequently see them written as `[ 1 -eq 2 ]`.
+
+`( .. )` is completely unrelated, and is a subshell mostly used to scope shell modifications. They should not be used in `if` or `while` statements in shell scripts.
+
+If you wanted to test a condition, rewrite the `( .. )` to `[ .. ]`. 
+
+### Exceptions:
+
+This error is triggered by having a binary operator as the first parameter in a subshell, and could falsely trigger on e.g. `if ( grep -eq "foo|bar" file )`. In these cases, check whether the subshell is actually needed.
+
+Note that there's a similar looking error [[SC2204]] with a low false positive rate.
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