The underscore variable is set at shell startup and contains the absolute file name of the shell or script being executed as passed in the argument list.

$_ 下划线变量在shell启动时设置，包含shell的绝对文件名或者作为参数列表被执行的脚本。

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Note that even in cases where a absolute file name is provided, this API still returns only that string that directly forms part of the file name, as shown in Listing 10.

之前的字符串。请注意，即使提供了绝对文件名，此api仍然仅会返回属于文件名的直接部分，如清单10中所示。

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All file-specifying commands allow both absolute and relative file names as arguments. GDB always converts the file name to an absolute file name and remembers it that way.

所有指定文件的命令允许用绝对路径或相对路径作为参数。GDB总是把他们转换为相对文件名，并且记住他们。

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