From: Robert Klemme <shortcutter@...>
Date: 2008-08-13T18:40:12+09:00
Subject: Re: regular expresson isue

2008/8/13 Raj Singh <neeraj.jsr@gmail.com>:
> I have following regular expression to parse time.
>
> ([0-9]|0[0-9]|1[012]):([0-9]|0[0-9]|[1-5][0-9])\s*(am|pm)

This seems overly complex, especially your minute matching. This can
be simplified at least to "\d?\d" or "\d{1,2}".

> 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?

Do you need this for direct matching of a string or scanning of larger
volumes of text?  Here's an alternative (untested):

%r{
  \b
  (0?\d|1[012])  # hour
  :
  ([0-5]\d)   # minute
  \s*
  (am|pm)
}xi

If you want to use this for matching you probably rather want

%r{
  \A
  (0?\d|1[012])  # hour
  :
  ([0-5]\d)  # minute
  \s*
  (am|pm)
  \z
}xi

Note, the comments can stay in there when copy and pasting.

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end