https://unix.stackexchange.com/questions/148892/using-sed-command-convert-only-first-character-in-specific-line-with-uppercase
$ echo "testing is tesw" | sed -r 's/(^[a-z]).*\1/T/'
The first letter and last letter of the line should be the same. In that
case delete the line. No output should be produced.
2 consecutive letters
echo "Testing" | egrep ([a-z])\1
https://www.tutorialspoint.com/unix_commands/chmod.htm
6/18 , 6/25, 7/2, 7/9 , 7/16, 23, 30 , 8/6, 13, 20
9/10 , 17,24, 10/1, 8 , 15, 22, 29 , 11/5 , 12