Because it finds at least one match to its two-character pattern on every line, the grep command outputs every line in the input file.

由于会在每行至少找到此双字符模式的一个匹配项，因此grep命令会输出输入文件中的每个行。

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To allow additional characters in user input, add those characters to the character class in the regular expression pattern.

若要允许使用者输入额外的字元，加入规则运算式的模式中的字元类别中的这些字元。

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