如何在Perl中只写一个文件的某些行？ [英] How can I write only certain lines of a file in Perl?

问题描述

我正在寻找一种方法来读取输入文件，并且只打印选择行到Perl中的输出文件。我要打印到输出文件的行都以 xxxx.xxxx.xxxx 开头，其中 x 是字母数字字符（句点是句点，而不是通配符）。这些线并不都具有相同的结束，如果这有区别。我想的像下面的（ if 语句是所有的真正缺失，只要我能告诉）。

I am looking for a way to read an input file and print only select lines to an output file in Perl. The lines I want to print to the output file all begin with xxxx.xxxx.xxxx, where x is an alphanumeric character (the periods are periods, not wildcards). The lines do not all have the same ending, if that makes a difference. I'm thinking something like the following (the condition of the if statement is all that is really missing as far as I can tell).

open(IN, "<$csvfile");
my @LINES = <IN>;
close(IN);
open(OUT, ">$csvnewfile");
print OUT @LINES if ([line starts with xxxx.xxxx.xxxx]);
close(OUT);

提前感谢！

推荐答案

这里是一个更好的方式循环通过你的线。它避免立即将您的整个输入文件加载到内存：

Here is a better way to loop through your lines. It avoids loading your whole input file into memory at once:

use strict;
use warnings;

open my $fhi, '<', $csvfile    or die "Can not open file $csvfile: $!";
open my $fho, '>', $csvnewfile or die "Can not open file $csvnewfile: $!";
while (<$fhi>) {
    print $fho $_ if m/^ \w{4} \. \w{4} \. \w{4} /x;
}
close $fho;
close $fhi;

请记住 \w 字符类还包括下划线。要避免下划线：

Keep in mind that the \w character class also includes underscores. To avoid underscores:

print $fho $_ if m/^ [a-z\d]{4} \. [a-z\d]{4} \. [a-z\d]{4} /xi;

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