regular expresson isue

[Raj Singh]

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)

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?

You can play with this regex at

http://www.rubular.com/regexes/863

 

[Shashank Agarwal]

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)

You want to match from the beginning of the string. So put a ^ before
your statement -

^([0-9]|0[0-9]|1[012])[0-9]|0[0-9]|[1-5][0-9])\s*(am|pm)

 

[Shadowfirebird]

Sorry to be the awkward one, but maybe you should consider handling
this programatically, rather than in a regex?

Pros: your code is likely to be easier to understand: that makes it
more maintainable.
Cons: your code will be longer.

From: Raj Singh [mailto:[email protected]]
# ([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 =3D /((^|\D)[0-9]|0[0-9]|1[012]):/
=3D> /((^|\D)[0-9]|0[0-9]|1[012]):/

irb(main):113:0> re =3D~ "1:"
=3D> 0
irb(main):114:0> re =3D~ " 1:"
=3D> 0
irb(main):117:0> re =3D~ "13:"
=3D> nil

irb(main):122:0> re =3D~ "01:"
=3D> 0
irb(main):123:0> re =3D~ "11:"
=3D> 0
irb(main):124:0> re =3D~ "12:"
=3D> 0

kind regards -botp

--=20
All you can do is try to know who your friends are as you head off to
the war / Pick a star on the dark horizon and follow the light

 

[Robert Klemme]

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