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+## In POSIX sh, $(<file) is undefined.
+
+(or "In dash, ... is not supported." when using `dash`)
+
+### Problematic code:
+
+```sh
+content=$(<file)
+```
+
+### Correct code:
+
+```sh
+content=$(cat file)
+```
+
+### Rationale:
+
+In bash and ksh, `$(< file)` will expand to the full contents of the file.
+
+However, in dash and POSIX sh, it will instead expand to nothing. This is because it's not recognized as special, and simply results in the command output of `< file`, a no-op command that opens the file and exits without reading it.
+ 
+### Exceptions:
+
+None.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!