From dcc1234511cb51901184e31b6d914d634176a8ef Mon Sep 17 00:00:00 2001
From: koalaman <vidar@vidarholen.net>
Date: Sun, 25 Jan 2015 12:17:29 -0800
Subject: [PATCH] Created SC2115 (markdown)

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 1 file changed, 21 insertions(+)
 create mode 100644 SC2115.md

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+## Use "${var:?}" to ensure this never expands to /* .
+
+### Problematic code:
+
+    rm -rf "$STEAMROOT/"*
+
+### Correct code:
+
+    rm -rf "${STEAMROOT:?}/"*
+
+### Rationale:
+
+If `STEAMROOT` is empty, this will [end up deleting everything](https://github.com/ValveSoftware/steam-for-linux/issues/3671) in the system's root directory.
+
+Using `:?` will cause the command to fail if the variable is null or unset. Similarly, you can use `:-` to set a default value if applicable.
+
+In the case command substitution, assign to a variable first and then use `:?`. This is relevant even if the command seems simple and obviously correct, since forks and execs can fail due to external system limits and conditions, resulting in a blank substitution. 
+
+### Exceptions:
+
+None.
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