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Editorial Team
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Asked: 2026-05-21T22:29:17+00:00

Anybody can help compose regular expression for this logic? MM/DD/YYYY hh:mm AM/PM MM/DD/YYYY hh

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Anybody can help compose regular expression for this logic?

MM/DD/YYYY hh:mm AM/PM 
MM/DD/YYYY hh AM/PM 
MM/DD/YYYY 
MM/YYYY 
YYYY

[Date templates] 

M/D/YY 
M/YY 
M/YYYY 
M/D/YYYY 

MMM YY 
MMM YYYY 
MMMM YY 
MMMM YYYY 

YY/M 
YY-M 
YY.M 

YYYY/M 
YYYY-M 
YYYY.M 

YYYY 

YYYY/M/D 
YYYY-M-D 
YYYY.M.D 

M-D-YY 
M-YY 
M-YYYY 
M-D-YYYY 

M.D.YY 
M.YY 
M.YYYY 
M.D.YYYY 

MMM D[,] YY 
MMM D[,] YYYY 

MMMM D[,] YY 
MMMM D[,] YYYY 

D MMM[,] YY 
D MMM[,] YYYY 

D MMMM[,] YY 
D MMMM[,] YYYY

[Time templates] 

hh:mm AM (or PM or A or P) 
hh AM (or PM or A or P) 
HH:mm 

YY two-digit year (00 => 2000, 10 => 2010)
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1 Answer

  1. Editorial Team

    To give you some hints:
    You have different ways to specify a month: M, MM, MMMM

    M means its a number, so you can write it like [0-9] (there are even more compact ways, but I think this requires the least explanation).

    MM means you can have another digit, but this digit can obviously only be 1, as 12 is the highest.

    So we alter the expression: 1?[0-9]. Which means the one is optional.

    Is this correct? No, because it would e.g. accept 0 as a valid month. So alter it again.

    (1[0-2]|[1-9]) which means: either a 1 followed by another digit between 0 and 2, so 10, 11, 12 are accepted. The braces are there to create a group.

    Now to accept MMMM

    (1[0-2]|[1-9]|January|February) etc.

    This can be further composed, e.g. for MM/YYYY and YYYY

    ((1[0-2]|[1-9]|January|February)/)?<YYYY-Pattern>

    Also don’t forget to match the start and the beginning:

    ^((1[0-2]|[1-9]|January|February)/)?<YYYY-Pattern>$

    otherwise you’d match things like abc MM/DD/YYYY bla

    If everything works, you should use non-capturing groups where you don’t need to reference the contents of a group. So ^((1[0-2]|[1-9]|January|February)/)?<YYYY-Pattern>$ becomes ^(?:(1[0-2]|[1-9]|January|February)/)?<YYYY-Pattern>$ because you probably don’t need to reference the group with the /. (However I think this is implementation dependent). To reference the groupse you probably want to give them names. Have a look here: http://www.regular-expressions.info/named.html

    Well that’s the way I compose regular expressions…

    Don’t give up, its going to be a longer expression, but not a very complex one.

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