Some shellchecks in basic-install.sh

[ChillerDragon]

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---

What does this PR aim to accomplish?:

Since there are shellcheck magic comments to disable rules might as well fix some warnings.

I reduced the warnings from

In basic-install.sh line 189:
        detected_os=$(grep "\bID\b" /etc/os-release | cut -d '=' -f2 | tr -d '"')
                            ^-- SC1117: Backslash is literal in "\b". Prefer explicit escaping: "\\b".
                                ^-- SC1117: Backslash is literal in "\b". Prefer explicit escaping: "\\b".


In basic-install.sh line 774:
    IPV6_ADDRESSES=($(ip -6 address | grep 'scope global' | awk '{print $2}'))
                    ^-- SC2207: Prefer mapfile or read -a to split command output (or quote to avoid splitting).


In basic-install.sh line 1023:
    local regex="^${ipv4elem}\.${ipv4elem}\.${ipv4elem}\.${ipv4elem}${portelem}$"
                             ^-- SC1117: Backslash is literal in "\.". Prefer explicit escaping: "\\.".
                                          ^-- SC1117: Backslash is literal in "\.". Prefer explicit escaping: "\\.".
                                                       ^-- SC1117: Backslash is literal in "\.". Prefer explicit escaping: "\\.".


In basic-install.sh line 2296:
    local latesttag
          ^-- SC2034: latesttag appears unused. Verify use (or export if used externally).


In basic-install.sh line 2371:
    if which dnsmasq &> /dev/null; then
       ^-- SC2230: which is non-standard. Use builtin 'command -v' instead.


In basic-install.sh line 2487:
    ftlLoc=$(which pihole-FTL 2>/dev/null)
             ^-- SC2230: which is non-standard. Use builtin 'command -v' instead.


In basic-install.sh line 2504:
    if which dnsmasq &> /dev/null; then
       ^-- SC2230: which is non-standard. Use builtin 'command -v' instead.


In basic-install.sh line 2525:
            localSha1=$(sha1sum "$(which pihole-FTL)" | cut -d ' ' -f 1)
                                   ^-- SC2230: which is non-standard. Use builtin 'command -v' instead.


In basic-install.sh line 2555:
                localSha1=$(sha1sum "$(which pihole-FTL)" | cut -d ' ' -f 1)
                                       ^-- SC2230: which is non-standard. Use builtin 'command -v' instead.

to

In basic-install.sh line 774:
    IPV6_ADDRESSES=($(ip -6 address | grep 'scope global' | awk '{print $2}'))
                    ^-- SC2207: Prefer mapfile or read -a to split command output (or quote to avoid splitting).


In basic-install.sh line 2486:
    ftlLoc=$(which pihole-FTL 2>/dev/null)
             ^-- SC2230: which is non-standard. Use builtin 'command -v' instead.


In basic-install.sh line 2524:
            localSha1=$(sha1sum "$(which pihole-FTL)" | cut -d ' ' -f 1)
                                   ^-- SC2230: which is non-standard. Use builtin 'command -v' instead.


In basic-install.sh line 2554:
                localSha1=$(sha1sum "$(which pihole-FTL)" | cut -d ' ' -f 1)
                                       ^-- SC2230: which is non-standard. Use builtin 'command -v' instead.

How does this PR accomplish the above?:

I only changed the obvious fixes that are known to not make any issues. The 4 left over warnings need a bit more elaborated fix and come with possible traps. For example command -v and which handle aliases different so when the output is needed not just the return code this can change behavior if pihole-FTL is an alias.

[yubiuser]

Closing and reopening to trigger the tests again.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pi-hole-ftl-v5-12-web-v5-9-and-core-v5-7-released/51795/1