LUA patterns to detect matching date

Question

I struggling to find the correct LUA code to detect if two dates appear after each other.

I have something similar which detects two keywords, but it's not working on my dates.

Here's the LUA code I have so far:

(%a+) %- %1$

Cheers,

Can you give an example of what you want to match? Also, what language are you working in? — Elmar Peise, Mar 15 '17 at 17:32
Please provide some examples of the text you are checking and the expected result. — Sam, Mar 15 '17 at 17:32
It seems you want to match repeat the same pattern with `%1` - no, this `%1` matches the same alpha characters matched with `(%a+)`. Try removing `$` end of string anchor. Please provide sample strings you are trying to match. BTW, what you are using is not regex, these are Lua patterns. — Wiktor Stribiżew, Mar 15 '17 at 17:36
I absolutely wouldn't use regex for this. It will be hard to get right, especially if it's possible for a date to be duplicated more than once. What tools/languages do you have at your disposal? — jpmc26, Mar 15 '17 at 17:51
Check http://ideone.com/1F1L9s, try `'^(%d+%-%d+%-%d+) %- %1$'` or `'(%d+%-%d+%-%d+) %- %1'` (if you want to match shorter substrings inside a longer string). — Wiktor Stribiżew, Mar 15 '17 at 18:20

Wiktor Stribiżew · Accepted Answer · 2017-03-15T18:30:20.240

Your main trouble here is that you want to match a date like 2017-03-19 with %a+ pattern. %a matches a letter, %a+ matches 1 or more letters.

You need to replace this pattern with a more precise one, like %d+%-%d+%-%d+ or %d%d%d%d%-%d%d%-%d%d:

'(%d+%-%d+%-%d+) %- %1'

where %d matches a digit.

Now, if you want to match a whole string like this, you need to enclose the pattern with ^ and $ anchors.

'^(%d+%-%d+%-%d+) %- %1$'

If you want to add word boundaries,

 '%f[%d](%d+%-%d+%-%d+) %- %1%f[%D]'

1 Answers1