传递有效数据，防止元字符的问题。
正则表达式通过元字符加强的字符和操作符构建。
Regular expressions are built from characters and operators, augmented by metacharacters.
这为我们带来了一个非常常见的问题：元字符漏洞。
This brings us to a very common problem — meta-character vulnerability.
什么其他元字符怎么办？
您已经看到过匹配所有空格字符的元字符，例如 \s。
You've seen metacharacters, such as \s, that match any whitespace characters.
这是因为这些应用程序使用的元字符概念稍微有点差异，如下所述。
That's because these applications use a slightly different metacharacter notation, as described below.
大部分字符与自身匹配，大部分元字符必须使用反斜杠(\)进行转义。
Most characters match themselves, and most metacharacters must be escaped using a backslash (\). The fundamental operations are.
假设您用于连接的用户有读取权限，还需要使用元字符~才能访问主目录中的信息。
The ~ meta-character should also work to access information from a home directory, providing the user you are using to connect has rights to read it.
元字符是正在表达式的本质，它是一类特殊的字符，下面展示了不同类型的元字符。
Metacharacters are special characters which are the essence of Regular Expressions. There are different types of metacharacters, described below.
设置crontab条目需要一个包含转义的shell元字符的字符串，所以适合于简单的命令和参数。
Setting up crontab entries requires a string with escaped shell metacharacters, so it is best done with simple commands and parameters.
要使过滤策略正确工作，Web开发人员需要确保的是，依照其应用程序的需要，过滤用的元字符列表是最新的。
For the filtering strategy to work properly, Web developers need to ensure that the list of metacharacters for filtering is up-to-date according to the needs of their applications.
元字符：元字符是在您所依赖的程序或库中——比如命令shell或者SQL——有特定含义的字符。
Metacharacters: Metacharacters are characters that have special meanings to programs or libraries you depend on, such as the command shell or SQL.
理解不同的测试并认识到shell还能把一些操作符解释成shell元字符，是成为高级shell用户的重要一步。
Understanding the various tests and knowing that the shell can also interpret some operators as shell metacharacters is an important step to becoming a power shell user.
SQL注入本质上与shell元字符的问题是相同的，不过它是由SQL解释器进行解释的，而不是由shell进行解释的。
SQL injection is essentially the same problem as the shell meta-character one, but with an SQL interpreter instead of the shell.
另一个有用的txt2regex选项是——showmeta，此选项可输出包含为所支持的应用程序构建regexp时使用的所有元字符的表。
Another useful txt2regex option is — showmeta, which outputs a table consisting of all the metacharacters used in building regexps for the supported applications.
但是如果您必须使用shell并且不能限制到达的数据，那么就需要在将命令中的字符发送到shell中之前对可能存在的每个元字符进行转义。
But if you must use the shell and you can't limit the data that comes in, you need to escape every potential meta-character before sending it in a command to the shell.
但是如果您必须使用shell并且不能限制到达的数据，那么就需要在将命令中的字符发送到shell中之前对可能存在的每个元字符进行转义。
But if you must use the shell and you can't limit the data that comes in, you need to escape every potential meta-character before sending it in a command to the shell.
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