how to get list of POSIX group members in Perl - perl

Question

Is there any way to get a list of all the members of a POSIX group in Perl?
I can't use getgrent() and similar because it returns the list as a space delimited string, and some usernames can have spaces in them.
I have to handle spaces in user and group names, because I'm working in an AD environment that other organizations can create users and groups in, so I'm trying to account for possible edge cases.

Answer 1

I'd say just use getgrent() and don't worry about spaces.
It may be possible to create a user name with one or more spaces in it, perhaps by manually editing /etc/passwd, but it's going to cause other problems as well. For example, ~foo is foo's home directory, but ~foo bar isn't foo bar's home directory.
On Linux, the useradd and adduser commands don't even permit spaces in file names. On Linux Mint 14 (based on Ubuntu 12.10):
$ sudo adduser 'foo bar'
adduser: To avoid problems, the username should consist only of
letters, digits, underscores, periods, at signs and dashes, and not start with
a dash (as defined by IEEE Std 1003.1-2001). For compatibility with Samba
machine accounts $ is also supported at the end of the username
$ sudo useradd !$
sudo useradd 'foo bar'
useradd: invalid user name 'foo bar'
$
Do you actually have user names with spaces on your system?
UPDATE: I've found that it actually is possible to create user names with spaces. useradd and adduser don't allow it (and you should be using one of those commands, or something similar, to create new accounts). But if I manually edit /etc/passwd using sudo vipw, I can create a user named foo bar, and I can do:
su - 'foo bar'
ssh 'foo bar#localhost'
etc. But it's a Really Bad Idea. Perl's getgr*() cannot tell whether a group contains one entry for foo bar or two entries for foo and bar (which is what you're asking about), and I can't use the shell's ~name syntax to refer to the account's home directory. I could use other methods to get both pieces of information, but it's much easier to avoid creating such an account in the first place.
If you're seriously concerned about some admin being foolish enough to create such an account, then you can use some of the alternative methods that have been discussed. But as I said, I don't think it's worth the effort.
(Perl could have avoided this problem by delimiting the list with : characters rather than spaces, since those are actually incompatible with the format of /etc/passwd and /etc/group, which the system depends on. But it's too late to change it now.)
UPDATE 2:
As you say in a comment (which I've edited into your question):
I have to handle spaces in user and group names, because I'm working in an AD environment that other organizations can create users and groups in, so I'm trying to account for possible edge cases.
Your solution from the same comment:
map((getgrgrid($_))[0], split(/ /, `id -G $username`))
is probably the best workaround. (id -G prints numeric group ids; which obviously can't contain spaces.)
It's probably also worth checking whether you actually have user or group names with spaces in them (though of course that doesn't guard against such names being added in the future). I wonder how your POSIX system actually deals with such names. I wouldn't be astonished if they're automatically translates them somehow. Even so, your id -G solution will still work.

Answer 2

If I have /etc/group:
...
postgres:x:26:
fsniper:x:481:
clamupdate:x:480:
some spacey group:x:482:saml, some spacey user
I can use the following commands to see this group's members:
% getent group
...
postgres:x:26:
fsniper:x:481:
clamupdate:x:480:
some spacey group:x:482:saml,some spacey user
Or if you know the specific group that you're interested in:
% getent group "some spacey group"
some spacey group:x:482:saml,some spacey user
These could be wrapped inside of a Perl script like this:
#!/usr/bin/perl
use feature qw(say);
chomp (my $getent = `getent group "some spacey group" | sed 's/.*://'`);
my #users = split(/,/, $getent);
foreach my $i (#users) { say $i; }
Running it:
% ./b.pl
saml
some spacey user
Resources
How to list all users in a Linux group?