expr is sometimes the only option

[ptman]

VERSION=$(expr "$VERSION" : '.*"\(1.[0-9\.]*\)["_]')
          ^-- expr is antiquated. Consider rewriting this using $((..)), ${} or [[ ]].

In this case the regular expression cannot be handled by the suggested mechanisms.

expr "$VERSION" \< 1.2 >/dev/null && continue
^-- expr is antiquated. Consider rewriting this using $((..)), ${} or [[ ]].

expr can compare floats

[koalaman]

On Bash, Ksh and Zsh, you can use [[ ]], but you're right in that there's no POSIX sh way of doing that. Shellcheck should probably not suggest this if you're using : and have specified #!/bin/sh

As for floats, POSIX specifically states that string comparison should be used when the arguments are not integers, unlike $(( .. )) where support for floats is allowed. Which shell/environment are you running this on?

[ptman]

I try to write POSIX /bin/sh scripts, for which some of the messages given by shellcheck are very helpful. You are correct that I could use string comparisons. And anyway there are lots of version numbers for which float (and string) comparison fails. I should probably use dpkg --compare-versions, but that's only available on Debian-derived systems ;)

[koalaman]

From 8d265aa, Shellcheck doesn't warn about expr when using :