July 07, 2005
Regular expression snippet for datetime format
Note that due to line-wrapping you may miss the embedded spaces in this. So to make it explicit there's a space after the date portion (that ends with "(?:0[5-9]|[1-2][0-9])") and there's a space followed by a question mark right before the "AM/PM" stuff.
Here you go, this is a long one...
If you're wondering what the "?:" is all about, it's a notation to the regex engine telling it to not worry about keeping track of any backreferences (which speeds things up). So "(?:expression)" means that the captured expression won't go into any \1 or $1 reference (if you don't need it), and the regex evaluation will run faster.
In Perl for example you'd use this expression to validate a variable holding a datetime value (making sure the variable is left- and right-trimmed of whitespace; or you can modify the regular expression to account for possible left- or right-whitespace), like this:
which means you're checking to see if the "$dt_str" variable value does not match the "{mess}" pattern (where {mess} is the long regular expression above).
Note that the year part as I've written it here validates for years from 2005 to 2029 (and the "20" is optional) which fits what I need it to do, so you may need to change the years being checked for your own needs. As I've written it it allows for a date format like "mm-dd/yy" or "mm/dd-yy" but to force consistency in the delimiters would have made it just so much longer and I didn't feel like that one was very important, because I can still get the relevant data from that. In Perl, you could force consistency on the delimiters like this
which forces the date delimiters to be dashes. Note also that the expression here allows for either AM/PM format or for military time (00:00:00 to 23:59:59), and it allows for upper- or lowercase AM/PM.
I hope this is useful to you.
Here you go, this is a long one...
/^(?:0?[1-9]|1[0-2])[-\/](?:0?[1-9]|[1-2][0-9]|3[0-1])[-\/](?:20)?(?:0[5-9]|[1-2][0-9]) (?:(?:0|0?[1-9]|1[0-1]):[0-5][0-9]:[0-5][0-9] ?(?:[AP]M[ap]m))(?:(?:0|0?[1-9]|1[0-9]|2[0-3]):[0-5][0-9]:[0-5][0-9])$/
If you're wondering what the "?:" is all about, it's a notation to the regex engine telling it to not worry about keeping track of any backreferences (which speeds things up). So "(?:expression)" means that the captured expression won't go into any \1 or $1 reference (if you don't need it), and the regex evaluation will run faster.
In Perl for example you'd use this expression to validate a variable holding a datetime value (making sure the variable is left- and right-trimmed of whitespace; or you can modify the regular expression to account for possible left- or right-whitespace), like this:
if ($dt_str !~ m/^{mess}$/)
which means you're checking to see if the "$dt_str" variable value does not match the "{mess}" pattern (where {mess} is the long regular expression above).
Note that the year part as I've written it here validates for years from 2005 to 2029 (and the "20" is optional) which fits what I need it to do, so you may need to change the years being checked for your own needs. As I've written it it allows for a date format like "mm-dd/yy" or "mm/dd-yy" but to force consistency in the delimiters would have made it just so much longer and I didn't feel like that one was very important, because I can still get the relevant data from that. In Perl, you could force consistency on the delimiters like this
$dt_str =~ s/^(\d?\d)[-\/](\d?\d)[-\/]((?:\d\d)?\d\d)/\1-\2-\3/;
which forces the date delimiters to be dashes. Note also that the expression here allows for either AM/PM format or for military time (00:00:00 to 23:59:59), and it allows for upper- or lowercase AM/PM.
I hope this is useful to you.
