Shell参数扩展需要说明

Question

I'm learning bash manual .

At page 27/166 , I really can't understand the last Parameter Expansion:

${parameter^pattern} 
${parameter^^pattern} 
${parameter,pattern}
${parameter,,pattern}

Can someone please tell me what these expansions mean?

Some examples would also be appreciated.

Answer 1

To lowercase

$ string="A FEW WORDS"
$ echo ${string,}
a FEW WORDS
$ echo ${string,,}
a few words

To uppercase

$ string="a few words"
$ echo ${string^}
A few words
$ echo ${string^^}
A FEW WORDS

Converting string to lower case in Bash shell scripting