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Date: Thu, 10 Apr 2014 14:20:09 -0600
From: Eric Blake <eblake@redhat.com>
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To: cygwin@cygwin.com
Subject: Re: Still testing needed: New passwd/group AD/SAM integration
References: <20140410145323.GB2437@calimero.vinschen.de> <5346B667.3040704@breisch.org> <20140410152809.GD2437@calimero.vinschen.de> <5346E55D.6020405@etr-usa.com> <20140410190424.GK2437@calimero.vinschen.de>
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On 04/10/2014 01:04 PM, Corinna Vinschen wrote:

>=20
> A local cygwin user told me that the users in their company would
> probably be confused by the '+ or, FWIW, any other non-backslash char,
> because they were drilled to see and use usernames always in domain\name
> form, or even in domain\\user form when logging in to Linux.
>=20
> I like slashes a lot more for obvious reasons.  But maybe, and that
> wouldn't be too hard to implement, we could accept account names with
> slash and with backslash, just as we do with pathnames.  Output of
> usernames would be with slashes, of course.

POSIX says:

http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html
> User Name
> A string that is used to identify a user; see also User Database. To be p=
ortable across systems conforming to POSIX.1-2008, the value is composed of=
 characters from the portable filename character set. The <hyphen> characte=
r should not be used as the first character of a portable user name.

It also says this for shell tilde expansion:

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#ta=
g_18_06_01
>  If none of the characters in the tilde-prefix are quoted, the characters=
 in the tilde-prefix following the <tilde> are treated as a possible login =
name from the user database. A portable login name cannot contain character=
s outside the set given in the description of the LOGNAME environment varia=
ble in XBD Other Environment Variables.

and following that link:
> For a value of LOGNAME to be portable across implementations of POSIX.1-2=
008, the value should be composed of characters from the portable filename =
character set.

In short, in POSIX systems, user names are solely from the set
[-_.a-zA-Z0-9]; which excludes +, \, or any other separator we come up
with.  I'm fine with using a non-portable character (this is, after all,
a cygwin extension of how to map Windows user names to a Linux emulation
environment).  But keeping in mind the rules on tilde expansion,

~a+b/file

can undergo tilde expansion for username 'a+b', but

~a\\b/file

cannot do so, because the \ is necessarily always quoted.  There is no
way to get tilde expansion to work for a username containing a shell
metacharacter, which frowns on quite a few otherwise useful characters,
including \.

Worse, the thought of using / as the separator gives me the willies - it
is BOUND to go wrong.  The expression

~a/b/file

is NOT requesting 'file' within user 'a/b's home, but 'b/file' within
user 'a's home.

--=20
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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