why this regex "^(0[1-9]|1[0-9]|2[0-9]|3[01])/(0[1-9]|1[012])/(19[0-9]{2}|20[0-1][0-7])$" fails for dates like 16/06/2008, 21/02/2008..?

Question

i was trying to match the dates starting from year 1900 to 2017 in dd/mm/yyyy format using this

^(0[1-9]|1[0-9]|2[0-9]|3[01])/(0[1-9]|1[012])/(19[0-9]{2}|20[0-1][0-7])$

regular expression but i am observing that this regular expression fails for dates like 16/06/2008 and 21/02/2008.
To make sure that all the parts of this regular expression are working or not i tried its all three parts like ^(0[1-9]|1[0-9]|2[0-9]|3[01])$ , ^(0[1-9]|1[012])$ and ^(19[0-9]{2}|20[0-1][0-7])$ on different sets of days months and years but i found that these are working fine but when i ran it combined i got same unexpected result for date like 16/06/2008.

Additionally i want to inform you that i am using this regex in javascript :

var patt = new RegExp("^(0[1-9]|1[0-9]|2[0-9]|3[01])/(0[1-9]|1[012])/(19[0-9]{2}|20[0-1][0-7])$");
var res = patt.exec(datestring);

for dates like 16/06/2008 res evaluates to null.

Please let me know where i am going wrong i? To solve this i have gone through some regular expression tutorials and previously asked questions but i did not find any relavent answer that can tell me why this regex fails for some specific dates. Please help.

You most probably want to change `(19[0-9]{2}|20[0-1][0-7])` to `(19[0-9]{2}|200[0-9]|201[0-7])` — Wiktor Stribiżew, Sep 13 '17 at 19:03
I think it would be best to not use regex but JS for this validation. — Redu, Sep 13 '17 at 19:03
For some jobs regular expressions are just the wrong tool. `31/02/2007` — Prinzhorn, Sep 13 '17 at 19:04
You might want to check [this](https://stackoverflow.com/q/5812220/4543207) topic to see why you can not do this job with pure regex. — Redu, Sep 13 '17 at 19:15
Thanks @WiktorStribiżew for your suggestion now it is working. — ProgBeginner, Sep 13 '17 at 19:21
But is there any online tool or software that shows all the possible match results for this kind of regular expression just to make sure that all the expected value are matching. — ProgBeginner, Sep 13 '17 at 19:25

score 9 · Answer 1 · answered Sep 13 '17 at 18:55

9

Because 2008 doesn't match 20[0-1][0-7]

answered Sep 13 '17 at 18:55

Andrey Belykh

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score 0 · Accepted Answer · answered Sep 13 '17 at 19:00

Along with

20[0-1][0-7]

not matching the year 2008 (8 does not fall in the range [0-7]) you may also want to escape the forward slashes in the regex by using a backslash as below

^(0[1-9]|1[0-9]|2[0-9]|3[01])\/(0[1-9]|1[012])\/(19[0-9]{2}|20[0-1][0-9])$

why this regex "^(0[1-9]|1[0-9]|2[0-9]|3[01])/(0[1-9]|1[012])/(19[0-9]{2}|20[0-1][0-7])$" fails for dates like 16/06/2008, 21/02/2008..?

2 Answers2