http://www.perlmonks.org?node_id=551238
 Description: Today I faced with small problem. I prepared a chart where data was split by weeks. It was very easy except one thing: display the first day of the week instead of week number. Here is a one way to do it (the main idea belongs to my co-worker Igor) P. S. Other way is to use Date::Calc - (\$y, \$m, \$d) = Monday_of_Week(\$week, \$year); Updated: added support of time zone.
```use Time::Local qw(timelocal timegm);
use POSIX qw(strftime);

sub get_date_by_week {
my \$week = shift || 1;
my \$year = shift || (localtime)[5];
my \$pattern = shift || '%d/%m';
my \$t = timegm(0, 0, 0, 1, 0, \$year);
my \$w = (gmtime(\$t))[6];
\$w = (\$w - 2) % 7 + 1;
my \$wc = \$week * 7 - \$w;
return strftime(\$pattern, localtime(\$t + \$wc * 24 * 3600));
}
```
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Re: Howto get the first day of the week by week number
by ikegami (Pope) on May 23, 2006 at 21:41 UTC

Not all days are of the same length in all time zones, so \$wc * 24 * 3600 is wrong. The simplest workaround is to use a time zone that doesn't have daylight savings time to do date calculations. For example, the following doesn't suffer from this bug:

```sub get_date_by_week {
my \$week = shift || 1;
my \$year = shift || (localtime)[5];
my \$pattern = shift || '%d/%m';
my \$t = timegm(0, 0, 0, 1, 0, \$year);
my \$w = (gmtime(\$t))[6];
\$w = (\$w - 2) % 7 + 1;
my \$wc = \$week * 7 - \$w;
return strftime(\$pattern, gmtime(\$t + \$wc * 24 * 3600));
}