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Help needed in writing Regular Expression

Raymand

Hi
I need some help in writing a Regular expression.
I am getting Date format like "Tue Apr 12 8:21:20 2009" I want to change this format to "Tue Apr 12 2009 8:21:20" using regular expression
Looking forward your help

Thanks

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Adam Stoller

Hi
I need some help in writing a Regular expression.
I am getting Date format like "Tue Apr 12 8:21:20 2009" I want to change this format to "Tue Apr 12 2009 8:21:20" using regular expression
Looking forward your help

Thanks

This is pretty trivial - have you tried reading about regex's on the web or in a book? Have you tried writing the regex yourself?

I (and many others here) could give you the regex easily - but it would be better if you at least tried something first and showed us what you tried.

neil_a

I agree with ghoti's statement about this being trivial, but I am happy to help you out.

There are multiple ways you can do this with a regex in perl, here is a basic way:


my $time = "Tue Apr 12 8:21:20 2009";
$time =~ s/(\d{1,2}:\d{1,2}:\d{1,2}) (\d{4})$/$2 $1/;
print $time;

You might also want to have a look at using a perl module (e.g. Date: Smiley Tongue

****) to do this. It might be a better option as it can handle multiple date formats.

Adam Stoller

I agree with ghoti's statement about this being trivial, but I am happy to help you out.

There are multiple ways you can do this with a regex in perl, here is a basic way:

my $time = "Tue Apr 12 8:21:20 2009"; $time =~ s/(\d{1,2}:\d{1,2}:\d{1,2}) (\d{4})$/$2 $1/; print $time;

You might also want to have a look at using a perl module (e.g. Date:****) to do this. It might be a better option as it can handle multiple date formats.

I kind of figured someone would post a regex - I was sort of going for the proverb:

Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime

That being said - you''ll never see a time-stamp with single digits for minutes and seconds - so the regex you posted could be somewhat simplified to

s/(\d{1,2}:\d{2}:\d{2})\s+(\d{4})$/$2 $1/

The above still assumes that the year is at the end of the string (based on what was originally posted, it's a reasonable assumption, but ...) - but I did modify it to accept 1-or-more white-space characters between the time-stamp and the year.

Date: Smiley Tongue

**** is good for taking a date-time-string and turning it into a full time string and vice-versa - it's not really for changing the format of a date-time-string. You could use Date::Manip too - but that would be way overkill. A regex is probably the most reasonable solution.

neil_a

Yes, teaching people to fish is a good idea. I believe you had the best intentions of helping in this matter, however regular expressions can be daunting to new users, and since it was trivial to me I didn't mind offering a solution.

My comments around using a perl module over a regular expression was regarding future-proofing the solution. Date: Smiley Tongue

**** handles multiple date formats, and once it is converted to a timestamp you can use parse it back into the format you like. I agree that this will be more overhead then a regex, but it will make things easier to handle if the input or output date change in the future - especially if you are not confident with regular expresions.

e.g.


use Date:****;
use POSIX qw(strftime);

my $time = str2time("Tue Apr 12 8:21:20 2009");
print strftime("%a %b %e %Y %H:%M:%S", localtime($time));

Adam Stoller

Yes, teaching people to fish is a good idea. I believe you had the best intentions of helping in this matter, however regular expressions can be daunting to new users, and since it was trivial to me I didn't mind offering a solution.

Yes - but unless someone is going to make an effort to understand them, they won't learn - and spoon-feeding the response is an easy way for them to avoid learning. The regex in question was pretty trivial and therefore all the more reason to use it as a learning experience IMO - but what's done is done - hopefully Raymond will still make an effort to learn, rather than just ask.

My comments around using a perl module over a regular expression was regarding future-proofing the solution. Date:**** handles multiple date formats, and once it is converted to a timestamp you can use parse it back into the format you like. I agree that this will be more overhead then a regex, but it will make things easier to handle if the input or output date change in the future - especially if you are not confident with regular expresions.

e.g.
use Date:****; use POSIX qw(strftime); my $time = str2time("Tue Apr 12 8:21:20 2009"); print strftime("%a %b %e %Y %H:%M:%S", localtime($time));

Ah - okay, that makes sense - it is, I think, a bit heavy-handed though in this case - but it would work.