Perl-while（<>）文件处理 [英] Perl - while (<>) file handling

问题描述

一个带有 while（<>）的简单程序处理作为参数给出的文件（ ./ program 1.file 2.file 3。文件）和Unix系统的标准输入。

A simple program with while( <> ) handles files given as arguments (./program 1.file 2.file 3.file) and standard input of Unix systems.

我认为它是将它们连接成一个文件，并且逐行进行。问题是，我怎么知道我正在使用第一个文件？然后是第二个。

I think it concatenates them together in one file and work is line by line. The problem is, how do I know that I'm working with the first file? And then with the second one.

举一个简单的例子，我想在一行中打印文件的内容。

For a simple example, I want to print the file's content in one line.

while( <> ){
    print "\n" if (it's the second file already);
    print $_;
}

推荐答案

钻石运算符不连接文件，它只是打开并连续读取它们。您如何控制它取决于您需要如何控制它。检查何时读取文件最后一行的一种简单方法是使用 eof ：

The diamond operator does not concatenate the files, it just opens and reads them consecutively. How you control this depends on how you need it controlled. A simple way to check when we have read the last line of a file is to use eof:

while (<>) {
    chomp;             # remove newline
    print;             # print the line
    print "\n" if eof; # at end of file, print a newline
}

跟踪您要处理的文件的顺序

You can also consider a counter to keep track of which file in order you are processing

$counter++ if eof;

请注意，此计数将在列表的最后一行处加一。文件，因此请不要过早使用它。

Note that this count will increase by one at the last line of the file, so do not use it prematurely.

如果要跟踪行号 $。当前文件句柄，您可以关闭 ARGV文件句柄来重置此计数器：

If you want to keep track of line number $. in the current file handle, you can close the ARGV file handle to reset this counter:

while (<>) {
    print "line $. : ", $_;
    close ARGV if eof;
}

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