Created SC2051 (markdown)

SC2051.md

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+## Bash doesn't support variables in brace expansions.
+
+### Problematic code:
+
+    for i in {1..$n}
+    do
+      echo "$i"
+    done
+
+### Correct code:
+
+    for ((i=0; i<n; i++))
+    do
+      echo "$i"
+    done
+
+### Rationale:
+
+In Bash, brace expansion happens before variable expansion. This means that brace expansion will never account for variables.
+
+Use an arithmetic for loop instead.
+
+### Contraindications
+
+None (if you're writing for e.g. zsh, make sure the shebang indicates this so shellcheck won't warn)