Regular expression

ruby-talk
1

I’m doing some html replacement using regular
expressions and i ran into this issue…

Example reg example => /[b](.*)[/b]/

…works fine to match bold please but NOT

with [b]bold

please[/b]

… where a new line is introduced so i tried this reg
exp…

/[b]([.\s]*)[/b]/

and this…
/[b]([.\n]*)[/b]/

but neither of the last 2 match at all.

What am i missing?

thanks,:stuck_out_tongue:

···

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2

That’s because ‘.’ doesn’t match newline by default. To get it to,
you need to add the /m flag. (You also need to have more than the one
line in the string, of course).

However, * is greedy, which means that given this text:

Here is some [b]bold text[/b], and here is [b]some more bold text[/b]

Your regex will match all the way from the first to the last ,
rather than just to the first [/b]. You can prevent that by using the
non-greedy qualifier ?, which goes after the *. Also, I would use %r
instead of /…/ just to avoid one of those nasty backslashes. :slight_smile:

So:

irb(main):001:0> x = “Here is some bold
irb(main):002:0" text, and here is some more
irb(main):003:0" bold text”
=> “Here is some bold\ntext, and here is some more\nbold text”
irb(main):004:0> x =~ %r{[b](.)[/b]}
=> nil
irb(main):005:0> x =~ %r{[b](.)[/b]}m
=> 13
irb(main):006:0> x.gsub(%r{[b](.)[/b]}m, ‘\1’/)
=> “Here is some bold\ntext[/b], and here is [b]some more\nbold text”
irb(main):007:0> x.gsub(%r{[b](.?)[/b]}m, ‘\1’/)
=> “Here is some bold\ntext, and here is some more\nbold text”

-Mark

···

On Wed, Sep 24, 2003 at 09:34:12AM +0900, paul vudmaska wrote:

I’m doing some html replacement using regular
expressions and i ran into this issue…

Example reg example => /[b](.*)[/b]/

…works fine to match bold please but NOT

with [b]bold

please[/b]

3
···

That’s because ‘.’ doesn’t match newline by default.
To get it to,
you need to add the /m flag. (You also need to have
more than the one
line in the string, of course).

However, * is greedy, which means that given this
text:

Here is some [b]bold text[/b], and here is [b]some

more bold
text[/b]

Your regex will match all the way from the first
to the last ,
rather than just to the first [/b]. You can prevent
that by using the
non-greedy qualifier ?, which goes after the *. Also,
I would use %r
instead of /…/ just to avoid one of those nasty
backslashes. :slight_smile:

<<

That great explanation and code worked like a champ.
Many thanks!

Paul

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