[Help-bash] Seemingly malformed but sane looking Bashism

[Rhys Ulerich]

Bash says...

$ echo ${foo:-$(echo a{b,c})}
bash: syntax error near unexpected token `)'
$ echo $BASH_VERSION
4.3.30(1)-release

..but to me, that looks well-formed:

$ echo ${foo:-default}
default
$ echo ${foo:-$(echo default)}
default
$ echo a{b,c}
ab ac

Is this a bug in the parser?

Coworkers have pointed out that these work as expected:

$ echo ${foo-`echo a{b,c}`}
ab ac
$ echo ${foo:-"$(echo a{b,c})"}
ab ac

- Rhys