Created SC2244 (markdown)

SC2244.md

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+## Prefer explicit -n to check non-empty string (or use =/-ne to check boolean/integer).
+
+### Problematic code:
+
+```sh
+if [ "$1" ]
+then
+  echo "True"
+fi
+```
+
+### Correct code:
+
+```sh
+# Check if $1 is empty or non-empty
+if [ -n "$1" ]
+then
+  echo "True, $1 is a non-empty value"
+fi
+
+# Check instead if $1 is true or false, as in Java
+[ "$1" = "true" ]
+
+# Check instead if $1 is non-zero or zero, as in C
+[ "$1" -ne 0 ]
+
+# Check instead if $1 is defined (even if just assigned the empty string) or undefined
+[ "${1+x}" = "x" ]
+
+```
+
+### Rationale:
+
+`[ "$var" ]` is equivalent to `[ -n "$var" ]` and checks whether the string is non-empty.
+
+Users more familiar with other languages are therefore often surprised to learn that `[ "$var" ]` is true when `var=false` or `var=0`.
+
+Adding the explicit `-n` helps clarify that this is a string comparison, and not related to any concept of boolean values or comparisons as it is in most languages.
+
+### Exceptions:
+
+If you are familiar with the semantics of `[`, you can [[ignore]] this suggestion with no ill effects.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!