Andrew Wheadon <andrew@wipux2.wifo.uni-mannheim.de> writes:

> 
> bugs:*:101:100:Bug Filer:/home/hiwis/bugs:/bin/go
> x11:*:102:100:Mr. X:/home/hiwis/x11:/bin/go
> lp:*:110:32766:Max Hit Lp:/var/spool/laser1:/bin/go
> tftp:*:113:32766:Trivial Ftp:/:/dev/null
> ftp:*:200:32766:Anonymous Ftp,,,:/mit/ftp:/dev/null
> anon:*:200:32766:Anonymous Sup,,,:/mit/ftp/pub/NetBSD:/dev/null
> httpd:*:202:40:Humpty Dumpty:/usr/local/etc/httpd:/dev/null
> 
> <root@wipux2:~> grep -v [a-z] /etc/passwd
> tftp:*:113:32766:Trivial Ftp:/:/dev/null
> <root@wipux2:~>
> 
> Why is grep outputting the 'tftp' line ?

Presumably you have at least one single-letter file name in the
current directory, and the letter(s) happen(s) to be present in the
other /etc/passwd entries.  Try some quotes.