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.file
) 和标准输入Unix 系统.
A simple program with while( <> )
handles files given as arguments (./program 1.file 2.file 3.file
) and standard input of Unix systems.
我认为它将它们连接在一个文件中,并且逐行工作.问题是,我怎么知道我正在处理第一个文件?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 "
" if (it's the second file already);
print $_;
}
推荐答案
菱形运算符不连接文件,它只是连续打开和读取它们.您如何控制这取决于您需要如何控制它.检查我们何时读取文件最后一行的简单方法是使用 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 "
" if eof; # at end of file, print a newline
}
您还可以考虑使用计数器来跟踪正在处理的文件
You can also consider a counter to keep track of which file in order you are processing
$counter++ if eof;
注意这个计数会在文件的最后一行增加一,所以不要过早使用它.
Note that this count will increase by one at the last line of the file, so do not use it prematurely.
如果你想跟踪当前文件句柄中的行号$.
,你可以close
ARGV文件句柄来重置这个计数器:
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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