string="abc"
final=${string//[a]/b}
echo $final
string="stirng" ; echo "${string//ir/ri}"
#1) Open the file in vi or vim
#2) Run the replacement command in vi (or vim) as follows
# Replace all matching patterns
:s%/PatternToReplace/Replacement
# Replace one matching pattern at a time
:s/PatternToReplace/Replacement
# echo "hello world" | tr " " .
hello.world