String replacement (to lowercase) in Bash 4.3.33

i'm trying change uppercase lowercase using string replacement in bash, i'm getting bad substitution error.

> a=hey > echo $a  hey  > echo ${a,,} -bash: ${a,,}: bad substitution # desired output hey

i've seen similar questions this, in cases down using earlier version of bash. i'm using gnu bash 4 , still having same problems.

> bash --version gnu bash, version 4.3.33(1)-release (x86_64-apple-darwin14.1.0)

this mac thing maybe? appreciated.

looks bash first in path happens 4.3.33, bash you're running in interactive session older version. run echo "$bash_version" check.

if above correct, run

type bash

to see path of newer version, /opt/local/bin/bash. i'll assume is. if want login shell, first add /etc/shells

sudo -e /etc/shells

after that, users allowed select login shell using chsh (change shell) command

chsh -s /opt/local/bin/bash

UV code