Error message: Unknown modifier encountered during date validation

Question

Error message: Unknown modifier encountered during date validation

I am currently using a specific string for validating dates in the formats 'dd/mm/yyyy' and 'dd-mm-yyyy':

'/^(0?[1-9]|[12][0-9]|3[01])[\/\.- ](0?[1-9]|1[0-2])[\/\.- ](19|20)\d{2}$/'

However, I encountered the following error:

Warning: preg_match() [function.preg-match]: Unknown modifier '\' in /var/www/...fields_lib.php on line 102

It's worth noting that the above string is entered into a web application's optional validation form field without any delimiters, as I believe the form itself adds the necessary delimiters. In cases of other validation types like integers and decimal numbers, I had to remove the delimiters for the validation to function properly on this particular form.

Any thoughts or suggestions would be greatly appreciated.

Thank you!

php regex preg-match

Answer 1

Answer №1

To improve your regex, you can remove the backslashes within character classes. Your updated regex should include [/. -]. Additionally, be mindful that the order of space and dash characters have switched places in this context, as [.- ] might mistakenly indicate "any character between period and space."

Answer 2

To improve your regex, you can remove the backslashes within character classes. Your updated regex should include [/. -]. Additionally, be mindful that the order of space and dash characters have switched places in this context, as [.- ] might mistakenly indicate "any character between period and space."

Answer 3

Answer №2

When encountering an error, I do not encounter the specified issue; instead, I am presented with an "out of order range" error, as explained by @CanSpice. To trigger the alternative error, I must eliminate the initial backslash in the character class ([/\.- ] rather than [\/\.- ]). This action causes the system to interpret the / as a regular expression delimiter, expecting the subsequent character to act as a modifier (such as i for case-insensitive or m for multiline).

In essence, there are two underlying issues at play: the misinterpretation of - as a range operator and the treatment of / as a regex delimiter. Both dilemmas can be resolved by escaping the problematic characters using backslashes (i.e.,

[\/.\- ]</code). However, each problem boasts a more elegant solution. By relocating <code>-

to a position where forming a range is impossible, it will be perceived as a literal -. As for the troublesome /, one can opt for an alternate regex delimiter, such as:

'~^(0?[1-9]|[12][0-9]|3[01])[/. -](0?[1-9]|1[0-2])[/. -](19|20)\d{2}$~'

It should be noted that the . did not require escaping at all. Within character classes, most regex metacharacters lose their special significance. Unfortunately, you stumbled upon two exceptions to this rule. :-/

Answer 4

When encountering an error, I do not encounter the specified issue; instead, I am presented with an "out of order range" error, as explained by @CanSpice. To trigger the alternative error, I must eliminate the initial backslash in the character class ([/\.- ] rather than [\/\.- ]). This action causes the system to interpret the / as a regular expression delimiter, expecting the subsequent character to act as a modifier (such as i for case-insensitive or m for multiline).

In essence, there are two underlying issues at play: the misinterpretation of - as a range operator and the treatment of / as a regex delimiter. Both dilemmas can be resolved by escaping the problematic characters using backslashes (i.e.,

[\/.\- ]</code). However, each problem boasts a more elegant solution. By relocating <code>-

to a position where forming a range is impossible, it will be perceived as a literal -. As for the troublesome /, one can opt for an alternate regex delimiter, such as:

'~^(0?[1-9]|[12][0-9]|3[01])[/. -](0?[1-9]|1[0-2])[/. -](19|20)\d{2}$~'

It should be noted that the . did not require escaping at all. Within character classes, most regex metacharacters lose their special significance. Unfortunately, you stumbled upon two exceptions to this rule. :-/

Error message: Unknown modifier encountered during date validation

Answer №1

Answer №2

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