Shell script cleanups

[practicalswift]

Shell script cleanups:

• Add required space to [ -n ].
• Avoid quote within quote.
• Exit if cd fails.
• Remove \n which is not handled by echo.
• Remove redundant $ in arithmetic variable expression.
• Use $(command) instead of legacy form `command`.
• Arrays are not supported in POSIX sh. Use bash when arrays are used.
• [ foo -a bar ] is not well defined, use [ foo ] && [ bar ] instead.
• [ foo -o bar ] is not well defined, use [ foo ] || [ bar ] instead.

[gmaxwell]

do we have someone on OpenBSD or likewise to test this?