cat  file.txt
Mike Harrington:(510) 548-1278:250:100:175
Christian Dobbins:(408) 538-2358:155:90:201
Susan Dalsass:(206) 654-6279:250:60:50
Archie McNichol:(206) 548-1348:250:100:175
Jody Savage:(206) 548-1278:15:188:150
Guy Quigley:(916) 343-6410:250:100:175
Dan Savage:(406) 298-7744:450:300:275
Nancy McNeil:(206) 548-1278:250:80:75
John Goldenrod:(916) 348-4278:250:100:175
Chet Main:(510) 548-5258:50:95:135
Tom Savage:(408) 926-3456:250:168:200
Elizabeth Stachelin:(916) 440-1763:175:75:300
 
只要4个字符姓名
awk  
 
 
length 用法  
 
awk '{if(length($1)==4 print $1} ' file.txt
 
 
--posix  参数 用法
 
awk --posix  '$1 ~/^[a-zA-Z]{4}$/{print $0}' file.txt