Mil Shell Separator
numfmt --grouping 12343423455.23353 # -> 12,343,423,455.23353
<previous command> | numfmt --grouping
Combative Crocodile
numfmt --grouping 12343423455.23353 # -> 12,343,423,455.23353
<previous command> | numfmt --grouping
$ echo "123456789" | sed ':a;s/\B[0-9]\{3\}\>/,&/;ta'
123,456,789