Parameter substitution bad substitution error on macOS High Sierra

Question

The ${parameter[^|^^|,|,,][pattern]} parameter substitution is giving me a bad substitution error.

$ echo $greeting
hello world
$ echo "${greeting^}."
-bash: ${greeting^}.: bad substitution

I updated to the latest bash version and keep getting the error.

GNU bash, version 4.4.19(1)-release (x86_64-apple-darwin17.3.0)

I've looked everywhere and the only suggestion I've found is making sure it's running bash 4.

$ echo $SHELL
/bin/bash

I'm running macOS High Sierra.

Answer 1

Your default shell is not the bash shell (downloaded from brew install bash) that contains the v4 which supports the parameter expansion syntax you are referring to.

On macOS echo $BASH_VERSION will tell you the version of the current shell. bash --version tells you the version of the first bash in your $PATH. So the way you were looking at the version was not telling you the version that you were running.

You need to add the recent version of bash to the file /etc/shells as the last line and use the command to set the shell as the default on Terminal

chsh -s /usr/local/bin/bash "$USER"

After this close and re-open the Terminal to make it effect. Without adding this default option in your Terminal, you could only use the recent bash only on scripts with interpreter she-bang set to #!/usr/local/bin/bash

See also this Ask Different answer to - Update bash to version 4.0 on OSX