SC3028 hostname utility is not in POSIX at all

[polluks]

For bugs with existing features

• Rule Id (SC3028):
• My shellcheck version (0.11.0):
• The rule's wiki page does not already cover this (e.g. https://shellcheck.net/wiki/SC3028)
• I tried on https://www.shellcheck.net/ and verified that this is still a problem on the latest commit

Here's a snippet or screenshot that shows the problem:

#!/bin/sh
hn=${HOSTNAME}
echo "$hn"
hn=$(HOSTNAME)
echo "$hn"

Here's what shellcheck currently says:

$(HOSTNAME) is okay

Here's what I wanted or expected to see:

use uname -n
see gwsw/less#770

[avih]

To clarify the issue, shellcheck correctly flags the use of $HOSTNAME in a /bin/sh script as non-POSIX, and links to https://shellcheck.net/wiki/SC3028 .

However, https://shellcheck.net/wiki/SC3028 recommends to use $(hostname) instead.

But the problem is that hostname is also not POSIX, which defeats the purpose of fixing a POSIX-compliance issue.

Instead, it could recommend to use $(uname -n) - which is POSIX.