Question

I want to validate a time with a regex. I created the following expression :

'#^([01][0-9])|(2[0-4])(:[0-5][0-9]){1,2}$#'

Here is the problem:

<?php
var_dump(preg_match('#^([01][0-9])|(2[0-4])(:[0-5][0-9]){1,2}$#', '14:25'));
// Returns 1 (OK)

var_dump(preg_match('#^([01][0-9])|(2[0-4])(:[0-5][0-9]){1,2}$#', '25:25'));
// Returns 0 (OK)

var_dump(preg_match('#^([01][0-9])|(2[0-4])(:[0-5][0-9]){1,2}$#', '14:2555'));
// Returns 1 (instead of 0 as I would like to get)
?>

Does anybody know what is wrong?

Answer 1

Time in 24-Hour format regular expression pattern :

([01]?[0-9]|2[0-3]):[0-5][0-9](:[0-5][0-9])?

The 24-hour clock format is start from 0-23 or 00-23 then a semi colon (:) and follow by 00-59 then (optionally a semi colon (:) and follow by 00-59).

Description :

(                  # start of group #1
  [01]?[0-9]       # start with 0-9,1-9,00-09,10-19
  |                # or
  2[0-3]           # start with 20-23
)                  # end of group #1
:                  # follow by a semi colon (:)
[0-5][0-9]         # follow by 0..5 and 0..9, which means 00 to 59
(                  # start of group #2
  :                # follow by a semi colon (:)
  [0-5][0-9]       # follow by 0..5 and 0..9, which means 00 to 59
)                  # end of group #2
?                  # optional third part

Matching time formats :

01:00, 02:00, 13:00,
 1:00,  2:00, 13:01,
23:59, 15:00,
00:00,  0:00,
14:34:43, 01:00:00

Not matching time formats :

 24:00             # hour is out of range [0-23]
 12:60             # minute is out of range [00-59]
  0:0              # invalid format for minute, at least 2 digits
 13:1              # invalid format for minute, at least 2 digits
  0:00:0           # invalid format for seconds, at least 2 digits
101:00             # hour is out of range [0-23]

Example :

var_dump(preg_match('#^[01]?[0-9]|2[0-3]):[0-5][0-9](:[0-5][0-9])?$#', '14:25'));    // OK
var_dump(preg_match('#^[01]?[0-9]|2[0-3]):[0-5][0-9](:[0-5][0-9])?$#', '25:25'));    // KO
var_dump(preg_match('#^[01]?[0-9]|2[0-3]):[0-5][0-9](:[0-5][0-9])?$#', '25:30'));    // KO
var_dump(preg_match('#^[01]?[0-9]|2[0-3]):[0-5][0-9](:[0-5][0-9])?$#', '14:2555'));  // KO
var_dump(preg_match('#^[01]?[0-9]|2[0-3]):[0-5][0-9](:[0-5][0-9])?$#', '14:65'));    // KO
var_dump(preg_match('#^[01]?[0-9]|2[0-3]):[0-5][0-9](:[0-5][0-9])?$#', '14:59'));    // OK
var_dump(preg_match('#^[01]?[0-9]|2[0-3]):[0-5][0-9](:[0-5][0-9])?$#', '14:34:43')); // OK