Well, FreeBSD 'adduser' IIRC displays the regexp that the username must conform to, but I am not at my FreeBSD box now so I can't check that, however here is my stab at a regexp you might need:

/^[A-Za-z][-.A-Za-z0-9_]+$/
[download]

This will force the first character to be a-z or A-Z and any other character a-z, A-Z, 0-9, -, . or _. It will also force the login name to be at least 2 characters (I'm not sure if this is what you want) and reject a username made up entirely of numbers (as the first character must be a-z or A-Z)

Hope this helps.

thanks, that sounds good. i'll give it a go

cheers guys.
how would i apply the maximum/minimum regexp to this expression:  if ($email !~ /.+\@.+\..+/) { ?

Use  .{2,10} instead of  .+ (if I did understand your question)

/^[A-Za-z][-.\w]+$/
[download]

thanks for that guys.
hotshot, is your rexexp missing out a _ or does the \w cater for that?

Just out of interest, is it possible to specify the minimum/maximum lengh of a variable using a regexp?
i.e, if i want the username to be no longer than 30 characters.

To make the username no longer than 30 characters use this:

/^[A-Za-z][-.\w]{1,29}$/
[download]

This will match when the first character is [A-Za-z] and is followed by 1 to 29 characters of form [-.\w] (thus making the total length of username from 2 to 30 characters)

And yes, \w caters for [a-zA-Z0-9_]

\w stands for a-z, A-Z, 0-9 and the underscore (_) os it answers your question.
about your second question, of course you can limit the string's length, for example if a username length should be maximum 30 characters long than this will qualify:

/^[A-Za-z][-.\w]{29}$/
[download]

the first char is mandetory to be alphabetic and the 29 in braces replaces the '+' sign to note exact number of chars.

Hotshot

What abut Unicode? Do you allow accented characters and the like? If so, then the standard range character classes are an outright bug (to loosely paraphrase Larry). Use the POSIX character classes for this.

Here is a regex using look ahead assertions and POSIX character classes which meets all of these requirements

$username = <>;
print "Yay!\n" if $username =~ /(?!    #look ahead . . .
                               ^    #and see if at the start of the st
+ring
                               \d+  #we have one or more digits
                               $)   #until the end of the string. If n
+ot . . .
                               ^    #at the start of the string
                   [[:alpha:]]   #allow an alphabetic character
                  [_.-0-9[:alpha:]]   #followed by an alphanumeric cha
+racter, underscore, dot, or dash
                           {0,29}   #0 to 29 times
                                $   #to the end of the string
                              /x;
[download]

Note: That if Unicode character are really not allowed (ie you actually DO want ASCII A-Za-z) then replace [:alpha:] in the example appropriately

Update: Not long after posting this I realized some mild errors if had because of an incomplete reading of jimbobn's original question. $face = red. This has been corrected Cheers,
Erik

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