Created SC2186 (markdown)

SC2186.md

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+## tempfile is deprecated. Use mktemp instead.
+
+### Problematic code:
+
+```sh
+tmp=$(tempfile)
+```
+
+### Correct code:
+
+```sh
+tmp=$(mktemp)
+```
+### Rationale:
+
+`tempfile` is a Debian specific utility for creating temporary files. Its man page notes:
+
+>tempfile is deprecated; you should use mktemp(1) instead.
+
+Neither `tempfile` nor `mktemp` are POSIX, but `tempfile` is Debian specific while `mktemp` works on GNU, OSX, BusyBox, *BSD and Solaris.
+
+### Exceptions:
+
+ShellCheck will not recognize when a function overrides this name.