如果该行与正则表达式匹配，则打印该行。
If the line matches the regular expression, then you print out that line.
这个功能非常简单，甚至不包含正则表达式匹配。
Its capability is very simple and does not even include regular expression matching.
注意：这不是grep使用的正则表达式匹配。
Note that this is not regular expression matching as used by grep.
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