Created SC2181 (markdown)

SC2181.md

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+## Check exit code directly with e.g. 'if mycmd;', not indirectly with $?.
+
+### Problematic code:
+
+```sh
+make mytarget
+if [ $? -ne 0 ]
+then
+  echo "Build failed"
+fi
+```
+
+### Correct code:
+
+```sh
+if ! make mytarget
+then
+  echo "Build failed"
+fi
+```
+### Rationale:
+
+Running a command and then checking its exit status `$?` against 0 is redundant.
+
+Instead of just checking the exit code of a command, it checks the exit code of a command (e.g. `[`) that checks the exit code of a command.
+
+To check that a command returns success, use `if mycommand; then ...`.
+
+To check that a command returns failure, use `if ! mycommand; then ...`.
+
+This also applies to `while`/`until` loops.
+
+### Exceptions:
+
+None.