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+## In POSIX sh, arrays are undefined.
+
+### Problematic code:
+
+```sh
+#!/bin/sh
+x=( foo bar "Hello World" )
+for word in "${x[@]}"
+do
+  touch "$word.dat"
+done
+```
+
+### Correct code:
+
+Consider switching to a shell that does support arrays, such as `bash` or `ksh`, by changing the shebang.
+
+Alternatively, if you only need a single array at a time, you may be able to rewrite to use the positional parameters:
+
+```sh
+set -- foo bar "Hello World"
+for word in "$@"
+do
+  touch "$word.dat"
+done
+```
+
+or strings with carefully chosen delimiters:
+
+```sh
+x='foo
+bar
+Hello World
+'
+
+printf '%s' "$x" |
+  while IFS='' read -r word
+  do
+    touch "$word.dat"
+  done
+```
+
+### Rationale:
+
+Arrays are specific to Bash and Ksh, but you are using them in a script declared to run with `sh` or `dash`. These shells do not support arrays at all. You should either switch to Bash/Ksh, or rewrite the script to not use arrays.
+
+There are no great replacements, especially not that can be mechanically applied, but using the positional parameters or a delimited string works in many cases, as shown in the examples. 
+
+### Exceptions:
+
+None.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!
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