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perltimestampreal-timesubroutine

Perl - How to generate an updating timestamp

I've gotten a decently functioning script going, and am happy with its results so far, thanks in large part to information I've found here.

However, one thing I cannot seem to get right is the timestamp. Currently, I am using this

use POSIX qw/strftime/;
my $timestamp = strftime('%m/%d/%Y %I:%M.%S %p %Z',localtime);

which works well, except that when I call $timestamp, it will always be the same timestamp for all parts of the code (doesn't update at all).

I attempted to remedy this with a subroutine (which I've never done before):

sub GetLoggingTime {
    use POSIX qw/strftime/;
    my $LoggingTime = strftime('%m/%d/%Y %I:%M.%S %p %Z',localtime);
    return $LoggingTime;
}

my $timestamp = GetLoggingTime();

print "$timestamp \n";
sleep(2);
print "$timestamp \n";

obviously the two prints and the sleep are to try and see if it is "updating", which it isn't. Both timestamps print with the same time.

I then tried to invoke the subroutine directly, adding a print within the subroutine and calling it using &GetLoggingTime, but that didn't do anything at all (no output).

I know I'm probably missing something obvious, but I just can't seem to find it. Is there a simple way to get that to work or is there a simple way to get a timestamp that updates in real time as the script progresses?

Thanks in advance!

Solution

  • You don't need to put the use statement inside your subroutine, that can be placed at the top of your program.

    Your code:

    my $timestamp = GetLoggingTime();

print "$timestamp \n";
sleep(2);
print "$timestamp \n";

    calls GetLoggingTime(), and stores the output inside $timestamp. Which means the value will remain static inside $timestamp. If you want to get the output of the present time each time, you will have to call GetLoggingTime() each time you need an updated value:

    my $timestamp = GetLoggingTime();
print "$timestamp \n";
sleep(2);
$timestamp = GetLoggingTime();
print "$timestamp \n";

    You can avoid using a variable by concatenating the result of GetLoggingTime() directly to your strings:

    print GetLoggingTime() . " \n";
sleep(2);
print GetLoggingTime() . " \n";

    or if your time stamp will always require a space and newline, you can include that inside GetLoggingTime()

    sub GetLoggingTime {
    return strftime('%m/%d/%Y %I:%M.%S %p %Z',localtime) . " \n";
}