Hopefully simple regex


#1

Hi,

I am trying to make a regex that will capture strings that look like
@string’ surrounded by whitespace or at the start or end of a line -
here is the spec:

require ‘test/unit’

class RegexTest < Test::Unit::TestCase

def setup
# this doesn’t work correctly for the fails scenarios
@regex = /(@{1,1}\w+)/
end

def test_regex_matches
str = [
@bar some more text”,
@bar”,
“sometext @bar text”,
“sometext @bar
]
str.each do |s|
s =~ @regex
assert_equal(’@bar’, $1)
end
end

def test_regex_fails
str = [
“@@bar”,
“sometext @@bar text”,
“sometext@bar text”,
“sometext@bar”
]
str.each do |s|
s =~ @regex
assert_equal(nil, $1)
end
end

end

I have tried all sorts of combinations of character class and negated
classes etc until my eyes have started glazing over - I really though
this should be easy - can anyone suggest a regex that pass my spec
above?

Thanks,

Stephen.


#2

On Dec 17, 10:15 pm, “stephen O’D” removed_email_address@domain.invalid wrote:

def setup
]
“sometext@bar text”,
I have tried all sorts of combinations of character class and negated
classes etc until my eyes have started glazing over - I really though
this should be easy - can anyone suggest a regex that pass my spec
above?

Thanks,

Stephen.

It seems like this regex works:

/^(?:.*\s+(@{1,1}\w+)|(@{1,1}\w+))/

Although you have to change the spec a little to check $1 and $2 for
matches. Still seems a bit over complex to me - any better
suggestions?


#3

Hi –

On Thu, 18 Dec 2008, stephen O’D wrote:

def setup

this doesn’t work correctly for the fails scenarios

@regex = /(@{1,1}\w+)/
end

I have tried all sorts of combinations of character class and negated
classes etc until my eyes have started glazing over - I really though
this should be easy - can anyone suggest a regex that pass my spec
above?

Try this:

@regex = /(?:^|\s)(@\w+)/

David


#4

On Wed, Dec 17, 2008 at 10:37 PM, stephen O’D
removed_email_address@domain.invalid wrote:

I have learned something from the last hour of trying!

http://www.rubular.com is an awesome way of composing and testing ruby
regular expressions. Highly recommended.


#5

Coming in 2009: The Well-Grounded Rubyist (http://manning.com/black2)
Perfect - I didn’t know you could (or even think to try) putting the
‘start of string’ anchor inside a group with an alternative! At least
I have learned something from the last hour of trying!