简体   繁体   English

chomp in perl没有按预期工作

[英]chomp in perl not working as expected

I found a strange behavior of chomp in Perl and I am unable to comprehend why is chomp is working like this. 我在Perl中发现了一个奇怪的chomp行为,我无法理解chomp为什么会像这样工作。

The following line does not work as expected 以下行无法按预期工作

if ( chomp($str1) eq chomp($str2) )

But, the following works fine 但是,以下工作正常

chomp $str1;
chomp $str2;
if ( $str1 eq $str2 )

Can you please give some insight in this behavior of chomp? 你能否对chomp的这种行为有所了解?

chomp modifies its argument. chomp修改了它的参数。 It does not return a modified argument. 它不会返回修改后的参数。 The second example is, in fact, how you're supposed to use it. 事实上,第二个例子就是你应该如何使用它。

edit : perldoc -f chomp says: 编辑perldoc -f chomp说:

   chomp   This safer version of "chop" removes any trailing string that
           corresponds to the current value of $/ (also known as
           $INPUT_RECORD_SEPARATOR in the "English" module).  It returns
           the total number of characters removed from all its arguments.

chomp返回已删除的字符数,而不是已被删除的字符串。

I like the name chomp() it's sound tells you what it does. 我喜欢名字chomp()它的声音告诉你它的作用。 As @ruakh mentions it takes one or more arguments, so you can say: 正如@ruakh所提到的,它需要一个或多个参数,所以你可以说:

chomp($str1,$str2);
if ( $str1 eq $str2 ) ...

You can also hand it an array of strings, like what you would get from reading a whole file at once, eg: 您也可以将其设置为一个字符串数组,就像您一次读取整个文件所获得的那样,例如:

chomp(@lines);

Generally, you can use s,$/$,,r regex as a non-destructive chomp. 通常,您可以使用s,$/$,,r regex作为非破坏性的chomp。 It removes record separator $/ from the end of $_ or the string provided using =~ , and returns the result without modifying anything. 它从$_的末尾删除记录分隔符$/或使用=~提供的字符串,并返回结果而不修改任何内容。 Your example would look like this: 您的示例如下所示:

if ( $str1 =~ s,$/$,,r eq $str2 =~ s,$/$,,r )

More formally the regex should be s,\\Q$/\\E$,,r , so $/ is not treated as regex. 更正式的正则表达式应该是s,\\Q$/\\E$,,r ,所以$/不被视为正则表达式。 In paragraph mode the regex would need to be s,\\n*$,,r . 在段落模式中,正则表达式需要是s,\\n*$,,r In slurp or fixed record mode the regex is not needed at all (chomp does nothing). 在slurp或固定记录模式下,根本不需要正则表达式(chomp什么都不做)。

声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.

 
粤ICP备18138465号  © 2020-2024 STACKOOM.COM