From: "Peña, Botp" <botp@...>
Date: 2008-08-13T11:40:37+09:00
Subject: Re: regular expresson isue

From: Raj Singh [mailto:neeraj.jsr@gmail.com] 
# ([0-9]|0[0-9]|1[012]):([0-9]|0[0-9]|[1-5][0-9])\s*(am|pm)
# I don't want this regext to match 13:45 PM because the the numerical
# value before the colon should be limited to 12. How to fix it?

Hi Raj,

the 13 is matching

  ([0-9]|0[0-9]|1[012])
   ^^^^^
   this

because the regex will match the 3. the regex did not care if it had a 1 before it.

You may want to tell it to not match any preceding digit (or else it be a beginning of the string) if you want a stand alone digit.
eg, you may want to achor/prefix it w the ^ (for beginning of string)
or \D (to represent a non-digit character)

sample tests,

irb(main):112:0> re = /((^|\D)[0-9]|0[0-9]|1[012]):/
=> /((^|\D)[0-9]|0[0-9]|1[012]):/

irb(main):113:0> re  =~ "1:"
=> 0
irb(main):114:0> re  =~ " 1:"
=> 0
irb(main):117:0> re  =~ "13:"
=> nil

irb(main):122:0> re  =~ "01:"
=> 0
irb(main):123:0> re  =~ "11:"
=> 0
irb(main):124:0> re  =~ "12:"
=> 0

kind regards -botp