Localtime How to Tell the Current Time in Perl

Perl has a handy built-in function for finding the current date and time in your scripts. However, when we talk about finding the time, were talking about the time that is currently set on the machine thats running the script. For instance, if youre running your Perl script on your local machine, localtime will return the current time you have set, and presumably set to your current timezone. When you run the same script on a web server, you may find that ​localtime there is off from ​localtime on your desktop system. The server might be in a different time zone or be set incorrectly. Each machine may have a totally different idea of what localtime is and it may take some adjusting, either within the script or on the server itself, to get it to match up to what youre expecting. The localtime function returns a list full of data about the current time, some of which will need to be adjusted. Run the program below and youll see each element in the list printed on the line and separated by spaces. #!/usr/local/bin/perltimeData localtime(time);print join( , timeData); You should see something similar to this, although the number could be very different. 20 36 8 27 11 105 2 360 0 These elements of the current time are, in order: Seconds past the minuteMinutes past the hourHours past midnightDay of the monthMonths past the start of the yearNumber of years since 1900Number of days since the start of the week (Sunday)Number of days since the start of the yearWhether or not daylight savings is active So if we return to the example and attempt to read it, youll see that its 8:36:20 AM on December the 27th, 2005, its 2 days past Sunday (Tuesday), and its 360 days since the start of the year. Daylight savings time is not active. Making the Perl Localtime Readable A few of the elements in the array that  localtime  returns are a bit awkward to read. Who would think of the current year in terms of the number of years past 1900?  Lets  take a look at an example that makes our date and time clearer. #!/usr/local/bin/perl months qw(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec); weekDays qw(Sun Mon Tue Wed Thu Fri Sat Sun); ($second, $minute, $hour, $dayOfMonth, $month, $yearOffset, $dayOfWeek, $dayOfYear, $daylightSavings) localtime(); $year 1900 $yearOffset; $theTime $hour:$minute:$second, $weekDays[$dayOfWeek] $months[$month] $dayOfMonth, $year; print $theTime; When you run the program, you should see a much more readable date and time like this: 9:14:42, Wed Dec 28, 2005 So what did we do to create this more readable version?  First,  we prepare two  arrays  with the names of the months and days of the week. months qw(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec); weekDays qw(Sun Mon Tue Wed Thu Fri Sat Sun); Since the  localtime  function returns these elements in values ranging from 0-11 and 0-6 respectively, they are perfect candidates for an array. The value returned by  localtime  can be used as a  numeric address  to access the correct element in the array. $months[$month] $weekDays[$dayOfWeek] The next step is to get all the values from the  localtime  function. In this example, were using a Perl shortcut to automatically place each element in the  localtime  array into its own variable. Weve chosen names so that its easy to remember which element is which. ($second, $minute, $hour, $dayOfMonth, $month, $yearOffset, $dayOfWeek, $dayOfYear, $daylightSavings) localtime(); We also need to adjust the value of the year. Remember that  localtime  returns the number of years since 1900, so in order to find the current year, well need to add 1900 to the value were given. $year 1900 $yearOffset; How to Tell the Current GM Time in Perl Lets say that you want to avoid all possible time zone confusions and take control of the offset yourself. Getting the current time in  localtime  will always return a value that is based on the machines timezone settings - a server in the US will return one time, while a server in Australia will return one nearly a full day different due to the time zone differences. Perl has a second handy time-telling  function  that works in exactly the same way as  localtime, but instead of returning the time fixed for  your machines time zone, it returns Coordinated Universal Time (abbreviated as UTC, also called Greenwich Mean Time or GMT). Simply enough the function is called  gmtime. #!/usr/local/bin/perl timeData gmtime(time); print join( , timeData); Other than the fact the time returned will be the same on every machine and in GMT, there is no difference between the  gmtime  and  localtime  functions. All the data and conversions are done in the same way. #!/usr/local/bin/perl months qw(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec); weekDays qw(Sun Mon Tue Wed Thu Fri Sat Sun); ($second, $minute, $hour, $dayOfMonth, $month, $yearOffset, $dayOfWeek, $dayOfYear, $daylightSavings) gmtime(); $year 1900 $yearOffset; $theGMTime $hour:$minute:$second, $weekDays[$dayOfWeek] $months[$month] $dayOfMonth, $year; print $theGMTime; localtime  will return the current local time on the machine that runs the script.gmtime  will return the universal Greenwich Mean Time, or GMT (or UTC).The return values may not be quite what you expect, so make sure you convert them as necessary.