Full best-practices / shellcheck-compliance pass

- Use modern `$()` syntax vs backticks [see [SC2006](https://github.com/koalaman/shellcheck/wiki/SC2006)]
- Always check for, and bail on, failures of `cd`. [see [SC2164](https://github.com/koalaman/shellcheck/wiki/SC2164)]
- Avoid `for foo in $(...)`, per [DontReadLinesWithFor](http://mywiki.wooledge.org/DontReadLinesWithFor)
- Avoid parsing `ls` to find subdirectories when `for d in "$dir"/*/` does the job; see also [ParsingLs](http://mywiki.wooledge.org/ParsingLs)
- `\s` is not specified in POSIX ERE (thus, not guaranteed to be available in bash-native regexes unless local platform's C library's regex implementation extends standard); use `[[:space:]]` instead.
- Avoid unnecessary deviations from POSIX sh specification:
   - `echo -e` violates (not just extends) POSIX, doesn't work as expected in bash compiled with `--enable-xpg-echo-default`; [POSIX specification](http://pubs.opengroup.org/onlinepubs/009604599/utilities/echo.html) suggests `printf` as replacement (see APPLICATION USAGE section).
   - `function` keyword not specified in POSIX, provides no benefit over standard-compliant syntax
3 files changed