Posts from August 2015.

.htaccess redirects based on date and time

A useful trick for implementing maintenance windows and redirects without having to use a php or similar script is to check date and time in .htaccess files or use it to build a redirect url.

Date and time values in .htaccess come in the form %{TIME_XXXX} where XXXX is the type of date or time you want.

So if you want to redirect a generic url to one which contains today’s date, you might use:

RewriteRule ^posts/today$ /posts/%{TIME_YEAR}-%{TIME_MON}-%{TIME_DAY}

That would result in /posts/today being redirected to something like /posts/2015-08-27

If you wanted redirect a page after a date (and time) is password you could use something like the following, where if the date is passed 9am on 27th August 2015 the redirect will happen. We use a simple number comparison of turning the date into an integer and then comparing it.

RewriteCond %{TIME_YEAR}%{TIME_MON}%{TIME_DAY}%{TIME_HOUR} >2015082709
RewriteRule ^$ /destination/url.html [R=301,L]

The following would only redirect until a specific time (10.22am on 27th August 2015)

RewriteCond %{TIME_YEAR}%{TIME_MON}%{TIME_DAY}%{TIME_HOUR}%{TIME_MIN} <201508271022
RewriteRule ^$ /destination/url.html [R=301,L]

The following would only redirect between two specific dates (20th July 2015 and 27th August 2015)

RewriteCond %{TIME_YEAR}%{TIME_MON}%{TIME_DAY} <20150828
RewriteCond %{TIME_YEAR}%{TIME_MON}%{TIME_DAY} >20150719
RewriteRule ^$ /destination/url.html [R=301,L]

The options you have for %{TIME_XXXX} values are:

TIME_YEAR // current four-digit year
TIME_MON // current month
TIME_DAY // current day of month
TIME_HOUR // current hour (24 hour clock) of day
TIME_MIN // current minute of hour
TIME_SEC // current second of minute
TIME_WDAY // current week-day
TIME // a formatted string representing the date and time down to seconds. e.g. 20150827112234

MySQL roughly random string generation for updating rows

Ever wanted to inject hashes into existing rows of a MySQL database? The code below allows you to generate a different string for each row affected by the update and choose the random string’s length from 1 to 32 character.

I’m aware it’s not the most random of generators but for url hashes etc, it works well. Be sure to then check for duplicates, which are possible!

Change 20 to a length between 1 and 32.

Update the WHERE condition to suit your needs

UPDATE table_name
SET column_name = (
SELECT substring(MD5(RAND()), -20)
WHERE condition_column = 1;