I have this file. Its a number at the start, then a name and a surname (someone can have 2 names or/and 2 surnames but not more)
21501 Sylvester Stallone
21502 Tommy Lee Jones
21503 Jean Claude Van Damme
I have to use grep. So far I have thought these 2 option I'm almost 100% sure none of them is right but it's a start.
grep -e [0-9]\{5\}[[:space:]][A-Z][a-z]
grep '^([a-z]+)[ \s]([a-z]+)/n'
grep -E -i '^[0-9]{5}( [a-z]+){2,4}$' filename
^ anchors the pattern to the beginning of the line. Then it looks for 5 digits, followed by 2-4 names each preceded by a space. $ anchors it to the end of the line.
-E makes it use extended regular expressions, and -i makes it case-insensitive so you don't need to say [A-Za-z].