Issues 78 - Makes install.sh more shellcheck compliant.

[Potherca]

Introduction

I was thinking about taking a stab at #53 but decided to make the relevant file more shellcheck compliant first (as suggested in issue #78).

Suggested Changes

Shellcheck Fixes

All occurrences of the following issues have been resolved:

• SC1054: You need a space after the '{'.
• SC2004: $ on variables in (( )) is unnecessary.
• SC2034: "variable" appears unused. Verify it or export it.
• SC2046: Quote this to prevent word splitting.
• SC2068: Double quote array expansions, otherwise they're like $* and break on spaces.
• SC2086: Double quote to prevent globbing and word splitting.
• SC2116: Useless echo? Instead of 'cmd $(echo foo)', just use 'cmd foo'.

Other issues

Whilst resolving shellcheck issues, I ran into two problems.

1. The call curl "${auth_param}" caused trouble when auth_param is empty (=''). This did not happen when there were no quotes around auth_param, that is to say, things accidentally worked.
   To resolve this I added a wrapper for the three use-cases around curl with a check and two variations of calling curl (one with and one without auth_param.
2. In some edge-cases the -o /dev/null will fail with a write error (curl error 23). However, failure to write to /dev/null is not an issue, as the HTTP status code is still viable. To resolve this I added a separate function for the "check url exists" logic and added the check there.

If these two solutions do not cause any trouble, I do believe they are worth keeping as they are a good first step in de-duplicating some of the curl calls.

Work for later

The following shellcheck issues are still present as I am unsure as how to resolve them:

• SC2059: Don't use variables in the printf format string. Use printf "..%s.." "$foo".
• SC2030: Modification of script is local (to subshell caused by (..) group).
• SC2031: script was modified in a subshell. That change might be lost.

I would suggest fixing those issues in a separate PR to keep things moving.

I'll continue work on #53 on a separate branch and open a PR once this has been merged to master.

[jwerle]

@Potherca thank you for this!

[jwerle]

Is this PR safe to merge in? Do you have anything else you'd like to add to it?

[Potherca]

I didn't feel too sure about the "gurl" curl wrapper so I cleaned that up by having two variations per function (wrapper) using curl.

Everything should be good to merge now.

[jwerle]

@Potherca awesome thanks!!