zsh is not splitting by IFS after parameter expansion

Question

This is my code to loop over colon separated values and do something with each value.

f()
{
    IFS=:
    for arg in $1
    do
        echo arg: $arg
    done
}

f foo:bar:baz

This works fine in most POSIX compliant shells.

$ dash foo.sh
arg: foo
arg: bar
arg: baz
$ bash foo.sh
arg: foo
arg: bar
arg: baz
$ ksh foo.sh
arg: foo
arg: bar
arg: baz
$ posh foo.sh
arg: foo
arg: bar
arg: baz
$ yash foo.sh
arg: foo
arg: bar
arg: baz

But it does not work as expected in zsh.

$ zsh foo.sh
arg: foo:bar:baz

Is zsh in violation of POSIX here?

Answer 1

Yes. Zsh has chosen its own way.

Here is the zsh faq entry: “3.1: Why does $var where var="foo bar" not do what I expect?”

In this particular case, you could workaround by adding the -y option to the zsh invocation:

$ zsh -y foo.sh
arg: foo
arg: bar
arg: baz

---

You could take a look at the zsh's faq especially the chapter 2 and 3. The more you've experienced other shells, the more you can find zsh's pitfalls.