Sed command to print date palindromes

Consider the following file called dates.txt containing some dates in US format, some of them palindromes (i.e., words that read the same backwards and forwards) and some not:

dates.txt
02/02/2020
03/02/2030
12/02/2021
06/19/1960
01/10/2010
03/07/2100

Write a one-line sed command that prints out only the lines containing date palindromes so that after running the appropriate sed command, the following would be output to the terminal:

02/02/2020
03/02/2030
12/02/2021

Here, I will use -E option so that I don't have to escape parenthesis and sed command looks better. In the question, it is mentioned to print the dates that are in palindrome for a date to become palindrome the day and the month must be written in the reverse order in place of year. p command is used for printing the words along with -n option to suppress unnecessary lines.

$sed -E -n '/([0-9])([0-9])\/([0-9])([0-9])\/\4\3\2\1/p' dates.txt

Recommended Posts