如何将Perl的本地时间与print一起使用以获得时间戳？ [英] How do I use Perl's localtime with print to get the timestamp?

问题描述

我使用以下语句获取当前时间。

 打印 $ query在本地时间成功执行； 
打印 $ query在，（localtime）成功执行； 
打印 $ query在成功执行。（本地时间）； 
  

输出

 在355516731103960成功执行
在355516731103960成功执行了
 2010年4月7日星期三成功执行了
  

前两个语句未以日期格式打印当前时间。
第三条语句仅以日期格式给出正确的输出。

我的理解是第一个语句在标量上下文中返回值，因此它返回数字

然后在第二张打印纸中，我仅在列表上下文中使用了本地时间，为什么它也给出了数字输出。 >解决方案

也许对于Perl编程而言，最重要的东西就是上下文。许多内置的子例程和运算符的行为因上下文而异。

  print $ query在本地成功执行 ， \n; ＃list context 
 print $ query在，（localtime）， \n成功执行； ＃列出上下文
打印 $ query在成功执行。当地时间 \n； ＃标量上下文
打印 $ query在。（localtime）， \n处成功执行； ＃标量上下文
 
打印 $ query在成功执行，标量本地时间， n； ＃标量上下文
打印 $ query在，标量（本地时间）， \n成功执行了； ＃标量上下文
  

这可以通过拆分语句来弄清楚。

 我的$ time =当地时间； ＃标量上下文
打印 $ query在$ time\n成功执行; 
 
 my @time =当地时间； ＃list context 
 print $ query在@ time\n成功执行; 
  

I have used the following statements to get the current time.

  print "$query executed successfully at ",localtime;
  print "$query executed successfully at ",(localtime);
  print "$query executed successfully at ".(localtime);

Output

 executed successfully at 355516731103960
 executed successfully at 355516731103960
 executed successfully at Wed Apr  7 16:55:35 2010

The first two statements are not printing the current time in a date format. Third statement only giving the correct output in a date format.

My understanding is the first one is returning a value in scalar context, so it is returning numbers.

Then in the second print I used localtime in list context only, why it's also giving number output.

解决方案

Perhaps the most important thing you can learn for programming in Perl, is context. Many built-in subroutines, and operators, behave differently depending on the context.

print "$query executed successfully at ", localtime, "\n"; # list context
print "$query executed successfully at ",(localtime),"\n"; # list context
print "$query executed successfully at ". localtime, "\n"; # scalar context
print "$query executed successfully at ".(localtime),"\n"; # scalar context

print "$query executed successfully at ", scalar  localtime, "\n"; # scalar context
print "$query executed successfully at ", scalar (localtime),"\n"; # scalar context

This can be made clearer by splitting up the statements.

my $time = localtime; # scalar context
print "$query executed successfully at $time\n";

my @time = localtime; # list context
print "$query executed successfully at @time\n";

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