How do I use Perl's localtime with print to get the timestamp?

Question

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.

Answer 1

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"; 

Answer 2

The return value of localtime depends on the context. In list context it is a 9-element list, while in scalar context it is a ctime(3) value:

my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime; my $now_string = localtime;  # e.g., "Thu Oct 13 04:54:34 1994" 

Now, print provides list context for its arguments. That's why print localtime outputs the numbers from the list (without any separator by default). You can force scalar context on localtime using either the . concatenation operator (like in your 3rd statement) or using scalar:

print "".localtime; print scalar localtime;