A file having dates in format “ 10/31/20”, and want to convert it to 31/10/2020.
sed 's#\([0-9][0-9]\)/\([0-9][0-9]\)/\([0-9][0-9]\)#\2/\1/20\3#' filename sed -E 's#([0-9]{2})/([0-9]{2})/([0-9]{2})#\2/\1/20\3#' filename
To cater for cases where the month or day is a single digit, such “ 1/31/20” then change the {2} to {1,2}.