Created SC3064 (markdown)

SC3064.md

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+## In POSIX sh, test -N is undefined.
+
+### Problematic code:
+
+```sh
+if [ -N file ]
+then
+  echo "File has been modified since last read"
+fi
+```
+
+### Correct code:
+
+```sh
+if bash -c '[ -N file ]'
+then
+  echo "File has been modified since last read"
+fi
+```
+### Rationale:
+
+`test -N` is not supported by POSIX, and there is no straight forward way of simulating it. If you need this functionality, look into which non-POSIX features your system has to allow this. `stat -c`, `find -printf`, bash, ksh, and Python are all possible options.
+
+Note that `atime` did not turn out to be as useful as first imagined in 1970, and it's generally better not to rely on it.
+
+### Exceptions:
+
+None. If you expect your shell to support `test -N`, either explicitly specify it in the shebang, use a `# shellcheck shell=bash` directive, or ignore this warning.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!