Created SC1088 (markdown)

SC1088.md

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+## Parsing stopped here. Invalid use of parentheses?
+
+### Problematic code:
+
+    grep ^(.*)\1$ file
+
+or
+
+    var = myfunction(value)
+
+### Correct code:
+
+    grep '^(.*)\1$' file
+
+or
+
+    var=$(myfunction value)
+
+### Rationale:
+
+Parentheses are shell syntax and must be used correctly.
+
+For commands that expect literal parentheses, such as `grep` or `find`, the parentheses need to be quoted or escaped so the shell does not interpret them, but instead passes them to the command.
+
+For shell syntax, the shell does not use them the way most other languages do, so avoid guessing at syntax based on previous experience. In particular:
+
+- Parentheses are NOT used to call functions.
+- Parentheses are NOT used to group expressions, except in arithmetic contexts.
+- Parentheses are NOT used in conditional statements or loops.
+- Parentheses are used differently in different contexts. `( .. )`, `$( .. )`, `$(( .. ))` and `var=(..)` are completely separate and independent structures with different meanings, and can not be broken down into operations on expressions in parentheses.
+
+  In C-like languages, `++` can't be broken down into two `+` operations, so you can't e.g. use `+ +` or `+(+)`. In the same way, all of the above are completely unrelated so that you can't do `$(1+1)` or `$( (1+1) )` in place of `$(( 1+1 ))`.
+
+If you are trying to use parentheses for shell syntax, look up the actual syntax of the statement you are trying to use.
+
+### Exceptions:
+
+None.