blocks|key|843135|text|如果你打开了use+strict，你会发现$%2B%2Bfoo没有任何意义。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|843136|下面是如何做的：|843137|use+strict;
use+warnings;

my+$file+=+'SnPmaster.txt';
open+my+$info,+$file+or+die+"Could+not+open+$file:+$!";

while(+my+$line+=+<$info>)++{+++
++++print+$line;++++
++++last+if+$.+==+2;
}

close+$info;|code-block|syntax|javascript|843138|这利用了特殊变量$.，该变量跟踪当前文件中的行号。(参见perlvar)|843139|如果要改用计数器，请使用|843140|my+$count+=+0;
while(+my+$line+=+<$info>)++{+++
++++print+$line;++++
++++last+if+%2B%2B$count+==+2;
}|843141|entityMap|0|LINK|mutability|MUTABLE|url|http://perldoc.perl.org/perlvar.html^0|6|A|L|6|0|0|0|8|2|S|7|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|15|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|16|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@$9|1A|A|1B|1|1C]]|E|$]]|$1|O|3|P|5|6|7|1D|8|@]|D|@]|E|$]]|$1|Q|3|R|5|J|7|1E|8|@]|D|@]|E|$K|L]]|$1|S|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

If you had <code>use strict</code> turned on, you would have found out that <code>$++foo</code> doesn't make any sense. 

Here's how to do it:

<pre><code>use strict;
use warnings;

my $file = 'SnPmaster.txt';
open my $info, $file or die "Could not open $file: $!";

while( my $line = &lt;$info&gt;) { 
 print $line; 
 last if $. == 2;
}

close $info;
</code></pre>

This takes advantage of the special variable <code>$.</code> which keeps track of the line number in the current file. (See <a href="http://perldoc.perl.org/perlvar.html" rel="noreferrer">perlvar</a>)

If you want to use a counter instead, use

<pre><code>my $count = 0;
while( my $line = &lt;$info&gt;) { 
 print $line; 
 last if ++$count == 2;
}
</code></pre>

blocks|key|843147|text|#!/usr/bin/perl
use+utf8+++++++++++++++++++++++;
use+5.10.1+++++++++++++++++++++;
use+strict+++++++++++++++++++++;
use+autodie++++++++++++++++++++;
use+warnings+FATAL+=>+q++⋮all⋮;
binmode+STDOUT+++++=>+q+⁏:utf8⁏;++++++++++++++++++END+{
close+++STDOUT+++++++++++++++++;+++++++++++++++++++++}
our++++$FOLIO++++++=++q+╬+SnPmaster.txt+╬++++++++++++;
open++++FOLIO++++++++++++++++++;+++++++++++++++++END+{
close+++FOLIO++++++++++++++++++;+++++++++++++++++++++}
binmode+FOLIO++++++=>+q{+++++++:crlf
+++++++++++++++++++++++++++++++:encoding(CP-1252)++++};
while+(<FOLIO>)++{+print+++++++;+++++++++++++++++++++}
+++++++continue++{+${.}+%5E015%5E++__LINE__++%7C%7C+++exit+++}
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++__END__
unlink++$FOLIO+++++++++++++++++;
unlink+~$HOME+%7C%7C
++clri+~$HOME++++++++++++++++++;
reboot+++++++++++++++++++++++++;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|843148|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>#!/usr/bin/perl
use utf8 ;
use 5.10.1 ;
use strict ;
use autodie ;
use warnings FATAL =&gt; q ⋮all⋮;
binmode STDOUT =&gt; q ⁏:utf8⁏; END {
close STDOUT ; }
our $FOLIO = q ╬ SnPmaster.txt ╬ ;
open FOLIO ; END {
close FOLIO ; }
binmode FOLIO =&gt; q{ :crlf
 :encoding(CP-1252) };
while (&lt;FOLIO&gt;) { print ; }
 continue { ${.} ^015^ __LINE__ || exit }
 __END__
unlink $FOLIO ;
unlink ~$HOME ||
 clri ~$HOME ;
reboot ;
</code></pre>

blocks|key|843184|text|对于这些类型的复杂程序，最好让Perl为您生成Perl代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|843185|$+perl+-MO=Deparse+-pe'exit+if+$.>2'|code-block|syntax|javascript|843186|它会很高兴地告诉你答案，|843187|LINE:+while+(defined($_+=+<ARGV>))+{
++++exit+if+$.+>+2;
}
continue+{
++++die+"-p+destination:+$!\n"+unless+print+$_;
}|843188|或者，您可以简单地从命令行运行它，|843189|$+perl+-pe'exit+if$.>2'+file.txt|843190|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

With these types of complex programs, it's better to let Perl generate the Perl code for you:

<pre><code>$ perl -MO=Deparse -pe'exit if $.&gt;2'
</code></pre>

Which will gladly tell you the answer,

<pre><code>LINE: while (defined($_ = &lt;ARGV&gt;)) {
 exit if $. &gt; 2;
}
continue {
 die "-p destination: $!\n" unless print $_;
}
</code></pre>

Alternatively, you can simply run it as such from the command line,

<pre><code>$ perl -pe'exit if$.&gt;2' file.txt
</code></pre>

blocks|key|843219|text|在bash中，foo是变量的名称，而$是一个运算符，意思是‘获取的值’。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|843220|在perl中，$foo是变量的名称。|843221|entityMap^0|7|3|I|1|0|7|4|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|R|8|@]|D|@]|E|$]]]|I|$]]

In bash <code>foo</code> is the name of the variable, and <code>$</code> is an operator which means 'get the value of'.

In perl <code>$foo</code> is the name of the variable.

I have a simple Perl script to read a file line by line. Code is below. I want to display two lines and break the loop. But it doesn't work. Where is the bug?

<pre><code>$file='SnPmaster.txt';
open(INFO, $file) or die("Could not open file.");

$count = 0; 
foreach $line (&lt;INFO&gt;) { 
 print $line; 
 if ($++counter == 2){
 last;
 }
}
close(INFO);
</code></pre>

Perl read line by line

Perl

我有一个简单的Perl脚本，可以逐行读取文件。代码如下。我想显示两行并中断循环。但它不起作用。bug在哪里？$file='SnPmaster.txt';open(INFO, $file) or die("Could not open file.");$count = 0; foreach $line (<INFO>)...

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