Bash 'shopt' doubt

Shell Programming and Scripting
1

Hi,

I am using bash shell's extended pattern matching.
What tweak the following code needs in order to get the expected output?

shopt -s extglob
f="a@b@_c@d@_e"
echo "${f/@(@|@_)/__}"

My expected output is:
a__b__c__d__e

but the actual output is:
a__b@_c@d@_e
# that is, how to make the change global as like echo $f | sed 's/@\|@_/__/g'

2

bash's extended pattern matching only works on filename expansion, not on parameter expansion.

3

In bash parameter expansion, do we have any such syntax as below?

echo "${!var*}"

consider, var is a variable previously set to some arbitrary string value

4

What do you want it to do?

I suggest that you read the Parameter Expansion section of the bash man page.