我正在编写一些可用于创建Linux用户帐户的Web UI页面。该Web UI将在CentOS 6（从RHEL
6派生）上使用。我发现关于什么构成有效的Linux用户名的信息不一致且不完整。我去了源代码，检查了Linux shadow-
utils源代码软件包，但我不能确保所查看的版本实际上与CentOS 6的版本相同。

以下是我当前使用的代码片段，其中包括从shadow-
utils软件包版本4.1.4.3复制/粘贴注释，加上我自己的一些注释以及Java正则表达式搜索，以使我了解阴影- utils来源。

chkname.c中引用的“
is_valid_name（）”检查显然不是Linux上的useradd命令所使用的，因为注释（和C代码源）不允许名称以数字开头。但是，useradd确实允许创建一个帐户，例如“
1234”。

我将不胜感激，从现在的内容到更正确的调整，以及有关如何通过一些稍有不同的is_valid_name函数实现useradd.c的信息，我们将不胜感激。

谢谢！艾伦

/**
 * Define constants for use in isNameLinuxCompatible(...) method.
 *
 * The source for the Linux compatible user name rule is is_valid_name(...) a function in the "shadow" package
 * for Linux.  The source file for that function has a comment as follows:
 *      User/group names must match [a-z_][a-z0-9_-]*[$]
 * That expression is a little loose/sloppy since
 * (1) the trailing $ sign is optional, and
 * (2) uppercase A-Z is also ok (and case is significant, 'A' != 'a').
 *
 * We deal with (1) by using the [$]? form where the ? means zero or more characters (aka "greedy").
 * We deal with (2) by using the CASE_INSENSITIVE option.
 *
 * Another way to express this is:
 *  1st character:                      a-z_         required at least one char
 *  chars other than first and last:    a-z0-9_-     optional
 *  last character:                     $            optional
 * Max length is 31.  Min length is 1.
 *
 * NOTE: The initial ^ and final $ below are important since we need the entire string to satisfy the rule,
 * from beginning to end.
 *
 * See http://download.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html for reference info on pattern matching.
 */

private static final String  LINUX_USERNAME_REGEX     = "^[a-z_][a-z0-9_-]*[$]?$";
private static final Pattern LINUX_USERNAME_PATTERN   = Pattern.compile(LINUX_USERNAME_REGEX, Pattern.CASE_INSENSITIVE);
private static final int     LINUX_USERNAME_MINLENGTH = 1;
private static final int     LINUX_USERNAME_MAXLENGTH = 31;

/**
 * See if username is compatible with standard Linux rules for usernames, in terms of length and
 * in terms of content.
 *
 * @param username the name to be checked for validity
 * @return true if Linux compatible, else false
 */
public boolean isNameLinuxCompatible (final String username) {
    boolean nameOK = false;
    if (username != null) {
        int len = username.length();
        if ((len >= LINUX_USERNAME_MINLENGTH) && (len <= LINUX_USERNAME_MAXLENGTH)) {
            Matcher m = LINUX_USERNAME_PATTERN.matcher(username);
            nameOK = m.find();
        }
    }
    return (nameOK);
}