Perl一线命令将EST时间转换为GMT时间

Question

I am trying to build a one line command in Perl to convert an EST datetime to GMT time and print the result. I'm using the module "DateTime" to accomplish this.

The command I tried is:

perl -MDateTime=set_Time_Zone -e "DateTime->new(year=>2019,month=>5,day=>10,hour=>18,minute=>40,time_zone=>EST)" -e "$dt->set_time_zone(GMT)"

The error it's throwing is

Can't call method "set_time_zone" on an undefined value at -e line 2.

How to call a method and print the hour in GMT?

Answer 1

Four problems:

1. DateTime doesn't export set_Time_Zone .
2. You use $dt without ever giving it a value. (This is what produces the error message.)
3. "EST" is not a standard time zone name, and should be avoided. It could refer to Eastern Standard Time (UTC-0500), a time zone that's mostly unused on May 10th. If so, specify -0500 instead.
4. You don't print anything.

---

If you really did mean Eastern Standard Time (despite it not being used on May 10th in places that observe DST), use the following:

perl -MDateTime -le'print DateTime->new(...,time_zone=>"-0500")->set_time_zone("UTC")'

It's far more likely that you meant Eastern Daylight Time. If so, use the following:

perl -MDateTime -le'print DateTime->new(...,time_zone=>"-0400")->set_time_zone("UTC")'

Instead of using fixed offsets, you can specify the geographically-based names from the tz database. When using these, DateTime factors in whether DST is used on the date-time in question and uses the appropriate offset. This is done as follows:

perl -MDateTime -le'print DateTime->new(...,time_zone=>"America/New_York")->set_time_zone("UTC")'

Finally, the following is how you'd tell DateTime to use the local time zone:

perl -MDateTime -le'print DateTime->new(...,time_zone=>"local")->set_time_zone("UTC")'

---

Notes:

• If you want a different output format, you can use ->strftime(...) .
• If using the Windows command shell, swap ' and " .

Answer 2

Where do you think $dt is set? And how is it gonna print without a print() ? Try:

perl -MDateTime=set_Time_Zone -e "print(DateTime->new(year=>2019,month=>5,day=>10,hour=>18,minute=>40,time_zone=>EST)->set_time_zone(GMT));"