Complex Regex finding date and time - regex

Is there someone to help me with the following:
I'm trying to find specific date and time strings in a text (to be used within VBA Word).
Currently working with the following RegEx string:
(?:([0-9]{1,2})[ |-])?(?:(jan(?:uari)?|feb(?:ruari)?|m(?:aa)?rt|apr(?:il)?|mei|jun(?:i)?|jul(?:i)?|aug(?:ustus)?|sep(?:tember|t)?|okt(?:ober)?|nov(?:ember)?|dec(?:ember)?))?(?: |-)?(?(3)(?: around | at | ))?(?:([0-9]{1,2}:[0-9]{1,2})?(?: uur| u|u)?)?
Tested output on following text:
date with around time: 26 sep 2016 around 09:00u
date with at time: 1 sep 2016 at 09:00 uur
date and time u: 1 sep 2018 09:00 u
time without date: 08:30 uur
date with time u: 1 sep 2016 at 09:00u
only time: 09:00
only month: jan
month and year: feb 2019
only day: 02
only day with '-': 2-
day and month: 2 jan
month year: jan 2018
date with '-': 2-feb-2018 09:00
other month: 01 sept 2016
full month: 1 september 2018
shortened year: jul '18
Rules:
a date followed by time is valid
a date followed by text 'around' or 'at', followed by time is valid
a date without day number is valid
a date without year is valid
a date, month only is not valid
a day, without month or year not valid
a date may contain dashes '-'
a year may be shortenend with ', like jun '18
month name can be short or long
full match includes ' uur' or 'u' (to highlight the text in ms-Word)
submatches text from capture are without prepending or trailing spaces
example at: [https://regex101.com/r/6CFgBP/1/]
Expected output (when using in VBA Word):
An regex Matches collection object in which each Match.SubMatches contains the individual items d, m, y, hh:mm from the capture groups in the regex search string.
So for example 1: the Submatches (or capture groups) contains values: '26' ','sep','2016','09:00'
The RegEx works fine, but some false-positives need to be excluded:
In case there is a day without month/year, should be excluded from Regex (example 9 and 10)
In case there is a month without day, should be excluded (example 7)
(I was trying with som lookahead and reference \1 and ?(1), but was not able to get it running properly...)
Any advice highly appreciated!

As I understood, you require that each date/time part (day, month, year, hour
and minute) must be present.
So you should remove ? after relevant groups (they are not optional).
It is also a good practice to have each group captured as a relevant capturing group.
There is no need to write something like jun(?:i)?. It is enough
(and easier to read) when you write just juni? (the ? refers just
to preceding i).
Another hint: As the regex language contains \d char class, use just
it instead of [0-9] (the regex is shorter and easier to read.
Optional parts (at / around) should be an optional and non-capturing group.
Anything after the minute part is not needed in the regex.
So I propose a regex like below (for readability, I divided it into rows):
(\d{1,2})[ -](jan(?:uari)?|feb(?:ruari)?|m(?:aa)?rt|apr(?:il)?|mei|juni?
|juli?|aug(?:ustus)?|sep(?:tember|t)?|okt(?:ober)?|nov(?:ember)?|dec(?:ember)?)
[ -](\d{4}) (?:around |at )?(\d{1,2}:\d{1,2})
Details:
(\d{1,2}) - Day.
[ -] - A separator after the day (either a space or a minus).
(jan(?:uari)?|...dec(?:ember)?) - Month.
[ -] - A separator after the month.
(\d{4}) - year.
(?:around |at )? - Actually, 3 variants of a separator between year
and hour (space / around / at), note the space before (...)?.
(\d{1,2}:\d{1,2}) - Hour and minute.
It matches variants 1, 2, 3, 5 and 13.
All remaining fail to contain each required part, so they are not matched.
If you allow e.g. that the hour/minute part is optional, change the respective fragment
into:
( (?:around |at )?(\d{1,2}:\d{1,2}))?
i.e. surround the space/around/at / hour / minute part with ( and )?,
making this part an optional group. Then, variants 14 and 15 will also
be matched.
One more extension: If you also allow the hour/minute part alone,
add |(\d{1,2}:\d{1,2}) to the regex (all before is the first variant and
the added part is the second variant for just hour/minute.
Then, your variants No 4 and 6 will also be matched.
For a working example see https://regex101.com/r/33t1ps/1
Edit
Following your list of rules, I propose the following regex:
(\d{1,2}[ -])? - Day + separator, optional.
(jan(?:uari)?|...|dec(?:ember)?) - Month.
(?:[ -](\d{4}|'\d{2}))? - Separator + year (either 4 or 2 digits with "'").
( (?:around |at )?(\d{1,2}:\d{1,2}))? - Separator + hour/minute -
optional end of variant 1.
|(\d{1,2}:\d{1,2}) - Variant 2 - only hour and minute.
It does not match only your variants No 9 and 10.
For full regex, including also "uur" see https://regex101.com/r/33t1ps/3

Finally I found something that helps me using the month properly :-)
\b(?:([1-3]|[0-3]\d)[ |-](?'month'(?:[1-9]|\d[12])|(?:jan(?:uari)?|feb(?:ruari)?|m(?:aa)?rt|apr(?:il)?|mei|jun(?:i)?|jul(?:i)?|aug(?:ustus)?|sep(?:tember|t)?|okt(?:ober)?|nov(?:ember)?|dec(?:ember)?))?)?(?:(\g'month')[ |-]((?:19|20|\')(?:\d{2})))?\b(?: omstreeks | om | )?(?:(\d{1,2}[:]\d{2}(?: uur|u)?|[0-2]\d{3}(?: uur|u)))?\b
It uses a named constructor/subroutine. Found here:
https://www.regular-expressions.info/subroutine.html

Related

How do I capture the Months with proper Regex?

How do I capture the days of months as numbers, excluding any suffixes. For instance - January 11th would be 11, and March 25th would be 25.
You could use the regex string and then only use the 3rd capturing group.
We accept 3 letter months Jan 1st and full name January 1st and accept space, hyphen,comma or slash as in Jan 01 Jan-01 Jan,1st Jan/31
(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)(uary|ruary|ch|il|e|y|ust|tember|ember)?[ \/,-]{0,2}([0-3]?[0-9])
You would do better to look for native time manipulation if possible.

REGEXP_EXTRACT specific string to extract year or month in Google Data Studio

I'm trying to categorize my sites but they have not always the same uri-structure so I want to extract the year in one column and in the second one I want to extract the month.
The results should be year and months in seperate columns/fields:
url
year
months
/www.site.com/path1/resort/2021/02/sitename
2021
02
/www.site.com/path1/2021/02
2021
02
/www.site.com/path1/2020/11-12
2020
11-12
/www.site.com/path1/2020/07-08
2020
07-08
/www.site.com/path1/resort/
null
null
the following regex for the year worked:
REGEXP_EXTRACT(url,'([0-9]{4})') >> result: 2020, null etc.
but the regex for the month didnt extract only the months:
REGEXP_EXTRACT(url,'((?:[0-9]{4}/)[0-9]+.?[0-9]*/)') >> result: 2020/11-12/,2021/02/, null etc.
Thanks for the help in advance.
You can use
(?:^|/)((?:19|20)[0-9]{2})/((?:0?[1-9]|1[0-2])(?:-(?:0?[1-9]|1[0-2]))?)(?:/|$)
See the regex demo.
If you need to capture only once per a match, replace the capturing group with non-capturing, or remove the extra pattern:
REGEXP_EXTRACT(col_url, '(?:^|/)((?:19|20)[0-9]{2})(?:/|$)') as Year
REGEXP_EXTRACT(col_url, '(?:^|/)((?:0?[1-9]|1[0-2])(?:-(?:0?[1-9]|1[0-2]))?)(?:/|$)') as Month
Details:
(?:^|/) - string start or /
((?:19|20)[0-9]{2}) - Group 1: a year, 19 or 20 followed with any two digits
/ - a / char
((?:0?[1-9]|1[0-2])(?:-(?:0?[1-9]|1[0-2]))?) - Group 2 (month): an optional 0 and then 1 to 9, or 1 and then 0 to 2 (00-12), and then an optional occurrence of - and the same month pattern
(?:/|$) - / or end of string.

Matching possible date elements in range

I'm having difficulty matching other cases for a date range. The end goal will be to extract each group to build an ISO 8601 date format.
Test cases
May 8th – 14th, 2019
November 25th – December 2nd
November 5th, 2018 – January 13th, 2019
September 17th – 23rd
Regex
(\w{3,9})\s([1-9]|[12]\d|3[01])(?:st|nd|rd|th),\s(19|20)\d{2}\s–\s(\w{3,9})\s([1-9]|[12]\d|3[01])(?:st|nd|rd|th),\s(19|20)\d{2}
regexr
I would like to be able to capture each group regardless if it exists or not.
For example, May 8th – 14th, 2019
Group 1 May
Group 2 8th
Group 3
Group 4
Group 5 14th
Group 6 2019
And November 5th, 2018 – January 13th, 2019
Group 1 November
Group 2 5th
Group 3 2018
Group 4 January
Group 5 13th
Group 6 2019
To capture the empty string if the group doesn't match otherwise, the general idea is to use (<characters to match>|)
Try this one:
([A-z]{3,9})\s((?:[1-9]|[12]\d|3[01])(?:st|nd|rd|th))(?:, (?=19|20))?(\d{4}|)\s–\s([A-z]{3,9}|)\s?((?:[1-9]|[12]\d|3[01])(?:st|nd|rd|th))(?:, (?=19|20))?(\d{4}|)
https://regex101.com/r/4UY0WE/1/
When trying to capture the month (the first group), make sure to use [A-z]{3,9} rather than \w{3,9}, otherwise you might match, eg, 23rd rather than a month string.
Separated out:
([A-z]{3,9}) # Month ("January")
\s
((?:[1-9]|[12]\d|3[01])(?:st|nd|rd|th)) # Day of month, including suffix ("23rd")
(?:, (?=19|20))? # Comma and space, if followed by year
(\d{4}|) # Year
\s–\s #
([A-z]{3,9}|) # same as first line
\s?
# same as third to fifth lines:
((?:[1-9]|[12]\d|3[01])(?:st|nd|rd|th))
(?:, (?=19|20))?
(\d{4}|)
This one saves some space by consolidating some of the groupings.
Try it here
Full regex:
([A-z]{3,9}) ((?:[1-9]|[12]\d|3[01])(?:st|nd|rd|th))(?:, ((?:19|20)\d{2}))? [–-] ([A-z]{3,9}\s)?((?:[1-9]|[12]\d|3[01])(?:st|nd|rd|th))(?:, ((?:19|20)\d{2}))?
Separated by group (spaces replaced by \s for readability):
1. ([A-z]{3,9})
\s
2. ((?:[1-9]|[12]\d|3[01])(?:st|nd|rd|th))
3. (?:,\s((?:19|20)\d{2}))?
\s[–-]\s
4. ([A-z]{3,9}\s)?
5. ((?:[1-9]|[12]\d|3[01])(?:st|nd|rd|th))
6. (?:,\s((?:19|20)\d{2}))?
This method does not use lookups so is generally safe for any regex engine.

Parsing dates from string - regex

I'm terible with regex and I can't seem to wrap my head around this simple task.
I need to parse out the two dates in a string which always has one of two formats:
"Inquiry at your property for December 29, 2013 - January 03, 2014"
OR
"Inquiry at your property for 29 December , 2013 - 03 January, 2014"
the 2 different date formats are throwing me off. Any insights would be appreciated!
/(\d+ \w+, \d+|\w+ \d+, \d+)/ for example. Try it out on Rubular.
For sure, it would pickup more stuff, like 2013 NotReallyAMonth, 12345. But if you don't have things in the input that look like a date, but not actually a date this might work.
You could make the regexp stronger, but applying more restrictions on what is matched:
/(\d{2} (?:January|December), \d{4}|(?:January|December) \d{2}, \d{4})/
In this case the day is always two digits, the year is 4. Months are listed explicitly (you would have to list all of them).
Update: For ranges it would be a different regexp:
/((?:Jan|Dec) \d+ - \d+, \d{4})/
Obviously they can all be combined together:
/(\d{2} (?:January|December), \d{4}|(?:January|December) \d{2}, \d{4}|(?:Jan|Dec) \d+ - \d+, \d{4})/

Regular Expression to match valid dates

I'm trying to write a regular expression that validates a date. The regex needs to match the following
M/D/YYYY
MM/DD/YYYY
Single digit months can start with a leading zero (eg: 03/12/2008)
Single digit days can start with a leading zero (eg: 3/02/2008)
CANNOT include February 30 or February 31 (eg: 2/31/2008)
So far I have
^(([1-9]|1[012])[-/.]([1-9]|[12][0-9]|3[01])[-/.](19|20)\d\d)|((1[012]|0[1-9])(3[01]|2\d|1\d|0[1-9])(19|20)\d\d)|((1[012]|0[1-9])[-/.](3[01]|2\d|1\d|0[1-9])[-/.](19|20)\d\d)$
This matches properly EXCEPT it still includes 2/30/2008 & 2/31/2008.
Does anyone have a better suggestion?
Edit: I found the answer on RegExLib
^((((0[13578])|([13578])|(1[02]))[\/](([1-9])|([0-2][0-9])|(3[01])))|(((0[469])|([469])|(11))[\/](([1-9])|([0-2][0-9])|(30)))|((2|02)[\/](([1-9])|([0-2][0-9]))))[\/]\d{4}$|^\d{4}$
It matches all valid months that follow the MM/DD/YYYY format.
Thanks everyone for the help.
This is not an appropriate use of regular expressions. You'd be better off using
[0-9]{2}/[0-9]{2}/[0-9]{4}
and then checking ranges in a higher-level language.
Here is the Reg ex that matches all valid dates including leap years. Formats accepted mm/dd/yyyy or mm-dd-yyyy or mm.dd.yyyy format
^(?:(?:(?:0?[13578]|1[02])(\/|-|\.)31)\1|(?:(?:0?[1,3-9]|1[0-2])(\/|-|\.)(?:29|30)\2))(?:(?:1[6-9]|[2-9]\d)?\d{2})$|^(?:0?2(\/|-|\.)29\3(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00))))$|^(?:(?:0?[1-9])|(?:1[0-2]))(\/|-|\.)(?:0?[1-9]|1\d|2[0-8])\4(?:(?:1[6-9]|[2-9]\d)?\d{2})$
courtesy Asiq Ahamed
I landed here because the title of this question is broad and I was looking for a regex that I could use to match on a specific date format (like the OP). But I then discovered, as many of the answers and comments have comprehensively highlighted, there are many pitfalls that make constructing an effective pattern very tricky when extracting dates that are mixed-in with poor quality or non-structured source data.
In my exploration of the issues, I have come up with a system that enables you to build a regular expression by arranging together four simpler sub-expressions that match on the delimiter, and valid ranges for the year, month and day fields in the order you require.
These are :-
Delimeters
[^\w\d\r\n:]
This will match anything that is not a word character, digit character, carriage return, new line or colon. The colon has to be there to prevent matching on times that look like dates (see my test Data)
You can optimise this part of the pattern to speed up matching, but this is a good foundation that detects most valid delimiters.
Note however; It will match a string with mixed delimiters like this 2/12-73 that may not actually be a valid date.
Year Values
(\d{4}|\d{2})
This matches a group of two or 4 digits, in most cases this is acceptable, but if you're dealing with data from the years 0-999 or beyond 9999 you need to decide how to handle that because in most cases a 1, 3 or >4 digit year is garbage.
Month Values
(0?[1-9]|1[0-2])
Matches any number between 1 and 12 with or without a leading zero - note: 0 and 00 is not matched.
Date Values
(0?[1-9]|[12]\d|30|31)
Matches any number between 1 and 31 with or without a leading zero - note: 0 and 00 is not matched.
This expression matches Date, Month, Year formatted dates
(0?[1-9]|[12]\d|30|31)[^\w\d\r\n:](0?[1-9]|1[0-2])[^\w\d\r\n:](\d{4}|\d{2})
But it will also match some of the Year, Month Date ones. It should also be bookended with the boundary operators to ensure the whole date string is selected and prevent valid sub-dates being extracted from data that is not well-formed i.e. without boundary tags 20/12/194 matches as 20/12/19 and 101/12/1974 matches as 01/12/1974
Compare the results of the next expression to the one above with the test data in the nonsense section (below)
\b(0?[1-9]|[12]\d|30|31)[^\w\d\r\n:](0?[1-9]|1[0-2])[^\w\d\r\n:](\d{4}|\d{2})\b
There's no validation in this regex so a well-formed but invalid date such as 31/02/2001 would be matched. That is a data quality issue, and as others have said, your regex shouldn't need to validate the data.
Because you (as a developer) can't guarantee the quality of the source data you do need to perform and handle additional validation in your code, if you try to match and validate the data in the RegEx it gets very messy and becomes difficult to support without very concise documentation.
Garbage in, garbage out.
Having said that, if you do have mixed formats where the date values vary, and you have to extract as much as you can; You can combine a couple of expressions together like so;
This (disastrous) expression matches DMY and YMD dates
(\b(0?[1-9]|[12]\d|30|31)[^\w\d\r\n:](0?[1-9]|1[0-2])[^\w\d\r\n:](\d{4}|\d{2})\b)|(\b(0?[1-9]|1[0-2])[^\w\d\r\n:](0?[1-9]|[12]\d|30|31)[^\w\d\r\n:](\d{4}|\d{2})\b)
BUT you won't be able to tell if dates like 6/9/1973 are the 6th of September or the 9th of June. I'm struggling to think of a scenario where that is not going to cause a problem somewhere down the line, it's bad practice and you shouldn't have to deal with it like that - find the data owner and hit them with the governance hammer.
Finally, if you want to match a YYYYMMDD string with no delimiters you can take some of the uncertainty out and the expression looks like this
\b(\d{4})(0[1-9]|1[0-2])(0[1-9]|[12]\d|30|31)\b
But note again, it will match on well-formed but invalid values like 20010231 (31th Feb!) :)
Test data
In experimenting with the solutions in this thread I ended up with a test data set that includes a variety of valid and non-valid dates and some tricky situations where you may or may not want to match i.e. Times that could match as dates and dates on multiple lines.
I hope this is useful to someone.
Valid Dates in various formats
Day, month, year
2/11/73
02/11/1973
2/1/73
02/01/73
31/1/1973
02/1/1973
31.1.2011
31-1-2001
29/2/1973
29/02/1976
03/06/2010
12/6/90
month, day, year
02/24/1975
06/19/66
03.31.1991
2.29.2003
02-29-55
03-13-55
03-13-1955
12\24\1974
12\30\1974
1\31\1974
03/31/2001
01/21/2001
12/13/2001
Match both DMY and MDY
12/12/1978
6/6/78
06/6/1978
6/06/1978
using whitespace as a delimiter
13 11 2001
11 13 2001
11 13 01
13 11 01
1 1 01
1 1 2001
Year Month Day order
76/02/02
1976/02/29
1976/2/13
76/09/31
YYYYMMDD sortable format
19741213
19750101
Valid dates before Epoch
12/1/10
12/01/660
12/01/00
12/01/0000
Valid date after 2038
01/01/2039
01/01/39
Valid date beyond the year 9999
01/01/10000
Dates with leading or trailing characters
12/31/21/
31/12/1921AD
31/12/1921.10:55
12/10/2016 8:26:00.39
wfuwdf12/11/74iuhwf
fwefew13/11/1974
01/12/1974vdwdfwe
01/01/99werwer
12321301/01/99
Times that look like dates
12:13:56
13:12:01
1:12:01PM
1:12:01 AM
Dates that runs across two lines
1/12/19
74
01/12/19
74/13/1946
31/12/20
08:13
Invalid, corrupted or nonsense dates
0/1/2001
1/0/2001
00/01/2100
01/0/2001
0101/2001
01/131/2001
31/31/2001
101/12/1974
56/56/56
00/00/0000
0/0/1999
12/01/0
12/10/-100
74/2/29
12/32/45
20/12/194
2/12-73
Maintainable Perl 5.10 version
/
(?:
(?<month> (?&mon_29)) [\/] (?<day>(?&day_29))
| (?<month> (?&mon_30)) [\/] (?<day>(?&day_30))
| (?<month> (?&mon_31)) [\/] (?<day>(?&day_31))
)
[\/]
(?<year> [0-9]{4})
(?(DEFINE)
(?<mon_29> 0?2 )
(?<mon_30> 0?[469] | (11) )
(?<mon_31> 0?[13578] | 1[02] )
(?<day_29> 0?[1-9] | [1-2]?[0-9] )
(?<day_30> 0?[1-9] | [1-2]?[0-9] | 30 )
(?<day_31> 0?[1-9] | [1-2]?[0-9] | 3[01] )
)
/x
You can retrieve the elements by name in this version.
say "Month=$+{month} Day=$+{day} Year=$+{year}";
( No attempt has been made to restrict the values for the year. )
To control a date validity under the following format :
YYYY/MM/DD or YYYY-MM-DD
I would recommand you tu use the following regular expression :
(((19|20)([2468][048]|[13579][26]|0[48])|2000)[/-]02[/-]29|((19|20)[0-9]{2}[/-](0[4678]|1[02])[/-](0[1-9]|[12][0-9]|30)|(19|20)[0-9]{2}[/-](0[1359]|11)[/-](0[1-9]|[12][0-9]|3[01])|(19|20)[0-9]{2}[/-]02[/-](0[1-9]|1[0-9]|2[0-8])))
Matches
2016-02-29 | 2012-04-30 | 2019/09/31
Non-Matches
2016-02-30 | 2012-04-31 | 2019/09/35
You can customise it if you wants to allow only '/' or '-' separators.
This RegEx strictly controls the validity of the date and verify 28,30 and 31 days months, even leap years with 29/02 month.
Try it, it works very well and prevent your code from lot of bugs !
FYI : I made a variant for the SQL datetime. You'll find it there (look for my name) : Regular Expression to validate a timestamp
Feedback are welcomed :)
Sounds like you're overextending regex for this purpose. What I would do is use a regex to match a few date formats and then use a separate function to validate the values of the date fields so extracted.
Perl expanded version
Note use of /x modifier.
/^(
(
( # 31 day months
(0[13578])
| ([13578])
| (1[02])
)
[\/]
(
([1-9])
| ([0-2][0-9])
| (3[01])
)
)
| (
( # 30 day months
(0[469])
| ([469])
| (11)
)
[\/]
(
([1-9])
| ([0-2][0-9])
| (30)
)
)
| ( # 29 day month (Feb)
(2|02)
[\/]
(
([1-9])
| ([0-2][0-9])
)
)
)
[\/]
# year
\d{4}$
| ^\d{4}$ # year only
/x
Original
^((((0[13578])|([13578])|(1[02]))[\/](([1-9])|([0-2][0-9])|(3[01])))|(((0[469])|([469])|(11))[\/](([1-9])|([0-2][0-9])|(30)))|((2|02)[\/](([1-9])|([0-2][0-9]))))[\/]\d{4}$|^\d{4}$
if you didn't get those above suggestions working, I use this, as it gets any date I ran this expression through 50 links, and it got all the dates on each page.
^20\d\d-(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)-(0[1-9]|[1-2][0-9]|3[01])$
This regex validates dates between 01-01-2000 and 12-31-2099 with matching separators.
^(0[1-9]|1[012])([- /.])(0[1-9]|[12][0-9]|3[01])\2(19|20)\d\d$
var dtRegex = new RegExp(/[1-9\-]{4}[0-9\-]{2}[0-9\-]{2}/);
if(dtRegex.test(date) == true){
var evalDate = date.split('-');
if(evalDate[0] != '0000' && evalDate[1] != '00' && evalDate[2] != '00'){
return true;
}
}
Regex was not meant to validate number ranges(this number must be from 1 to 5 when the number preceding it happens to be a 2 and the number preceding that happens to be below 6).
Just look for the pattern of placement of numbers in regex. If you need to validate is qualities of a date, put it in a date object js/c#/vb, and interogate the numbers there.
I know this does not answer your question, but why don't you use a date handling routine to check if it's a valid date? Even if you modify the regexp with a negative lookahead assertion like (?!31/0?2) (ie, do not match 31/2 or 31/02) you'll still have the problem of accepting 29 02 on non leap years and about a single separator date format.
The problem is not easy if you want to really validate a date, check this forum thread.
For an example or a better way, in C#, check this link
If you are using another platform/language, let us know
Perl 6 version
rx{
^
$<month> = (\d ** 1..2)
{ $<month> <= 12 or fail }
'/'
$<day> = (\d ** 1..2)
{
given( +$<month> ){
when 1|3|5|7|8|10|12 {
$<day> <= 31 or fail
}
when 4|6|9|11 {
$<day> <= 30 or fail
}
when 2 {
$<day> <= 29 or fail
}
default { fail }
}
}
'/'
$<year> = (\d ** 4)
$
}
After you use this to check the input the values are available in $/ or individually as $<month>, $<day>, $<year>. ( those are just syntax for accessing values in $/ )
No attempt has been made to check the year, or that it doesn't match the 29th of Feburary on non leap years.
If you're going to insist on doing this with a regular expression, I'd recommend something like:
( (0?1|0?3| <...> |10|11|12) / (0?1| <...> |30|31) |
0?2 / (0?1| <...> |28|29) )
/ (19|20)[0-9]{2}
This might make it possible to read and understand.
/(([1-9]{1}|0[1-9]|1[0-2])\/(0[1-9]|[1-9]{1}|[12]\d|3[01])\/[12]\d{3})/
This would validate for following -
Single and 2 digit day with range from 1 to 31. Eg, 1, 01, 11, 31.
Single and 2 digit month with range from 1 to 12. Eg. 1, 01, 12.
4 digit year. Eg. 2021, 1980.
A slightly different approach that may or may not be useful for you.
I'm in php.
The project this relates to will never have a date prior to the 1st of January 2008. So, I take the 'date' inputed and use strtotime(). If the answer is >= 1199167200 then I have a date that is useful to me. If something that doesn't look like a date is entered -1 is returned. If null is entered it does return today's date number so you do need a check for a non-null entry first.
Works for my situation, perhaps yours too?