UID 0 and getpwnam

c has asked for the wisdom of the Perl Monks concerning the following question:

I am writing a cgi script that allows input from a user to add a username in a formfield. I was using my $uid = getpwnam("$username"); to grab the uid of the user submitted. This worked well enough, until I was testing to see what happened when "root" was placed in the user field. Since the uid for root is "0", the $uid value was coming back as false and appearing as though the user didnt exist. Is there a(nother| better) way to test for the existance of a user that will encompass 'root'?

humbly -c

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Re: UID 0 and getpwnam by VSarkiss (Monsignor) on Apr 09, 2002 at 15:24 UTC
You're confusing the concepts of "defined" versus "false", which are very different in Perl. The `getpwnam` document mentions If the entry doesn't exist you get the undefined value. Thus, you need a test as mirod has outlined above. The same consideration applies anytime a value that represents falsehood in Perl (`0` or the empty string) can be a legitimate return result from a function. One of my favorite Perl books, Effective Perl Programming has an excellent section on the difference.	[reply] [d/l] [select]
Re: UID 0 and getpwnam by mirod (Canon) on Apr 09, 2002 at 15:13 UTC
Couldn't you use `if( defined $uid)`?	[reply] [d/l]
Re: UID 0 and getpwnam by thelenm (Vicar) on Apr 09, 2002 at 15:21 UTC
When I try your line of code on my machine using a non-existent username, I get a return value of `''` (not `undef`). If you're testing for the existence of a user, then, you should be able to test `length $uid`. If the return string has any length, then you have a valid user. I would also recommend removing the double-quotes around `$username`, as this causes double-quotish processing to happen, which you may not want.	[reply]
Re: UID 0 and getpwnam by gregorovius (Friar) on Apr 09, 2002 at 15:46 UTC
You should be able to test as follows `if( $uid >= 0 ) { ... }` [download] and cover all the valid cases.	[reply] [d/l]
Re: UID 0 and getpwnam by particle (Vicar) on Apr 09, 2002 at 17:09 UTC
a nit: it's extra work putting double quotes around variables like `"$username"`. basically, you're telling perl to build `'"' . $username . '"'`. in this function call, which is a waste of time. don't use double-quotes unless you need them. as an aside, in perl 6, you'll be able to do something like* `module module_name; my class NoData is Exception { method warn(@args) { die @args } } my $uid = getpwnam($username) // fail NoData;` [download] which will raise an exception of type NoData (a class localized to your module) if `getpwnam($username)` returns an undefined value. then leave it to the NoData class to handle the exception appropriately. as per Exegesis 4 ~Particle ;Þ	[reply] [d/l] [select]