The default NAME_REGEX value in /etc/adduser.conf is incorrect

[Ｖ字龍(Vdragon)]

Refer the Debian bug report for more information.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=630750

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: adduser 3.113+nmu3ubuntu3
ProcVersionSignature: Ubuntu 3.16.0-22.29-lowlatency 3.16.4
Uname: Linux 3.16.0-22-lowlatency i686
NonfreeKernelModules: nvidia
ApportVersion: 2.14.1-0ubuntu3.5
Architecture: i386
CurrentDesktop: KDE
Date: Fri Oct 31 01:55:03 2014
InstallationDate: Installed on 2013-03-08 (600 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release i386 (20121017.2)
PackageArchitecture: all
SourcePackage: adduser
UpgradeStatus: Upgraded to trusty on 2014-04-19 (194 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Andrew Meyer (andrewm-bpi)]

This just bit me. It's especially confusing for beginners because the config file syntax looks a lot like bash, and in bash that extra backslash would be correct as it would simply prevent the proceeding dollar symbol from being interpreted as an environment variable, and the backslash wouldn't show up in the final regex.

[Andrew Meyer (andrewm-bpi)]

Another example of someone getting confused by this bug: https://askubuntu.com/q/892419/166655

[Benjamin Drung (bdrung)]

It's fixed in 3.119 and therefore fixed in adduser 3.121ubuntu1 in Ubuntu 22.10 (kinetic).