Strictly speaking, ash does not support it.
From https://wiki.ubuntu.com/DashAsBinSh#A.5B.5E.5D
Not to be confused by sed's and other program's regular expression
syntax. Uses of [^...] in case (parameter/word expansion in general) need
to be replaced with [!...].
Found with shellcheck: https://github.com/koalaman/shellcheck/wiki/SC2169
Signed-off-by: Rosen Penev <rosenp@gmail.com>
[minor commit title/message adjustments]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
b9246bbdc9