Regular expression for string.anotherstring

ruby-talk
1

I'm trying to validate a user mail address for a fixed domain with the rule
string =~ /\w+\.\w+/
this matches firstname.lastname, which is what I want.
But it also matches fistname.lastname@somedomain.com, which is not what I
want. Why does that match? I'm having this in Rails, but I guess the
quoting will not escape @ signs?

Bart

2

Bart Braem wrote:

I'm trying to validate a user mail address for a fixed domain with the
rule string =~ /\w+\.\w+/
this matches firstname.lastname, which is what I want.
But it also matches fistname.lastname@somedomain.com, which is not what I
want. Why does that match? I'm having this in Rails, but I guess the
quoting will not escape @ signs?

I think you want this: "string.string", but you don't want this:
"string.string@domain". Yes?

Have you tried:

string =~ /^\w+\.\w+$/

"^" means match at the beginning of the string, "$" means match at the end.
IOW the example must match the entire string. Is this what you wanted?

···

--
Paul Lutus
http://www.arachnoid.com

3

I'm no regex master but what about:
/^[^@]+/

One or more things thats not an '@' at the beginning of the string?

hth,
-Harold

···

On 9/15/06, Bart Braem <bart.braem@gmail.com> wrote:

I'm trying to validate a user mail address for a fixed domain with the rule
string =~ /\w+\.\w+/
this matches firstname.lastname, which is what I want.
But it also matches fistname.lastname@somedomain.com, which is not what I
want. Why does that match? I'm having this in Rails, but I guess the
quoting will not escape @ signs?

Bart

4

Actually "$" matches at the end of the string or the first line break
('\n') whichever comes first.

\z literally matches at the end of the string, whereas
\Z matches either the end of the string unless the string ends with
'\n' in which case it matches just before that final '\n'

And if you want to match just before the first of an optional series
of trailing '\n's I think that this:

    \n*\Z

works as the end of the RE.

···

On 9/15/06, Paul Lutus <nospam@nosite.zzz> wrote:

Bart Braem wrote:

> I'm trying to validate a user mail address for a fixed domain with the
> rule string =~ /\w+\.\w+/
> this matches firstname.lastname, which is what I want.
> But it also matches fistname.lastname@somedomain.com, which is not what I
> want.

Have you tried:

string =~ /^\w+\.\w+$/

"^" means match at the beginning of the string, "$" means match at the end.
IOW the example must match the entire string. Is this what you wanted?

--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/

5

Paul Lutus wrote:

I think you want this: "string.string", but you don't want this:
"string.string@domain". Yes?

That's right.

Have you tried:

string =~ /^\w+\.\w+$/

"^" means match at the beginning of the string, "$" means match at the
end. IOW the example must match the entire string. Is this what you
wanted?

That's a good suggestion, I'll give it a shot.
One question though: why does \w match with '@'? According to the
documentation \w == [a..zA..Z]??

Bart

6

Bart Braem wrote:

One question though: why does \w match with '@'? According to the
documentation \w == [a..zA..Z]??\w doesn't match @, it's just that your expression was too general:

test = lambda { |x| p $1 if x =~ /(\w+\.\w+)/ }
test.call('down@fraggle.roc') # => "fraggle.roc"
test.call('foo.bar@baz') # => "foo.bar"

I.e., you were matching on either side of the @

Regards,
Jordan

7

Bart-

Maybe I'm off base here, but are you trying to determine if a string
matches a pattern, or are you trying to capture a matching substring
from a string?

-Alex

···

On 9/17/06, Bart Braem <bart.braem@gmail.com> wrote:

Paul Lutus wrote:

> I think you want this: "string.string", but you don't want this:
> "string.string@domain". Yes?
>
That's right.

> Have you tried:
>
> string =~ /^\w+\.\w+$/
>
> "^" means match at the beginning of the string, "$" means match at the
> end. IOW the example must match the entire string. Is this what you
> wanted?

That's a good suggestion, I'll give it a shot.
One question though: why does \w match with '@'? According to the
documentation \w == [a..zA..Z]??

Bart

8

MonkeeSage wrote:

I.e., you were matching on either side of the @

Oh boy, you are right! Thanks for the explanation.
I will try it with:
string =~ /^\w+\.\w+\z/

But is there a ruby operator to look for matches on the entire string?

Thanks for your help
Bart

9

Bart Braem wrote:

MonkeeSage wrote:

I.e., you were matching on either side of the @

Oh boy, you are right! Thanks for the explanation.
I will try it with:
string =~ /^\w+\.\w+\z/

But is there a ruby operator to look for matches on the entire string?

string =~ /^\w+\.\w+$/

Must match the entire string. Because of multiline issues, where that is a
factor, you can always split on newlines in advance of this test to be sure
you are matching the entire string unambiguously.

···

--
Paul Lutus
http://www.arachnoid.com

10

Hi --

MonkeeSage wrote:

I.e., you were matching on either side of the @

Oh boy, you are right! Thanks for the explanation.
I will try it with:
string =~ /^\w+\.\w+\z/

"Are you sure?\nabc.def" =~ /^\w+\.\w+\z/ # :slight_smile:

Keep in mind that ^ matches the beginning of any line.

But is there a ruby operator to look for matches on the entire string?

Do you mean scanning the string repeatedly? If so, then you can use
String#scan. If you mean anchoring a regex to the beginning of the
string, then you can use \A and \z (or \Z if you want to discount a
possible ending newline).

David

···

On Mon, 18 Sep 2006, Bart Braem wrote:

--
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails" [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog) [2] | Co-director, Ruby Central, Inc. [4]
[1] Ruby for Rails | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com | [4] http://www.rubycentral.org

11

Paul Lutus schrieb:

Bart Braem wrote:

I will try it with:
string =~ /^\w+\.\w+\z/

But is there a ruby operator to look for matches on the entire string?

string =~ /^\w+\.\w+$/

Must match the entire string. Because of multiline issues, where that is a
factor, you can always split on newlines in advance of this test to be sure
you are matching the entire string unambiguously.

This would be unnecessarily complex. Just use Bart's regexp (with \z instead of $). It matches the entire string.

Regards,
Pit

12

dblack@wobblini.net wrote:

But is there a ruby operator to look for matches on the entire string?

Do you mean scanning the string repeatedly? If so, then you can use
String#scan. If you mean anchoring a regex to the beginning of the
string, then you can use \A and \z (or \Z if you want to discount a
possible ending newline).

I meant that I want to do input validation on the entire string. It must
correspond to the format defined by the regular expression, no more, no
less.
That's why the newline part is not important here: I can't permit newlines.
You are right about the ^ at the beginning, I will be using
test =~ /\A\w+\.\w+\z/

Thanks a lot for the great input!
Bart

13

Pit Capitain wrote:

Paul Lutus schrieb:

Bart Braem wrote:

I will try it with:
string =~ /^\w+\.\w+\z/

But is there a ruby operator to look for matches on the entire string?

string =~ /^\w+\.\w+$/

Must match the entire string. Because of multiline issues, where that is
a factor, you can always split on newlines in advance of this test to be
sure you are matching the entire string unambiguously.

This would be unnecessarily complex.

Not really.

···

-----------------------------------

#!/usr/bin/ruby

s = "this is\na test\nstring."

a =

a << s.sub(/(^.*$)/,"\\1")

a << s.sub(/(^.*\z)/,"\\1")

a << s.sub(/(^.*$)/m,"\\1")

a << s.sub(/(^.*\z)/m,"\\1")

a.each do |s|
  puts "[#{s}]"
end

-----------------------------------

Output:

[this is
a test
string.]
[this is
a test
string.]
[this is
a test
string.]
[this is
a test
string.]

Just use Bart's regexp (with \z
instead of $). It matches the entire string.

My point is that, if there are embedded linefeeds and they are an issue,
they must be dealt with. Also, I don't immediately see a difference in
behavior between \z and $, contrary to the documentation's specification
that one matches the end of a line and the other matches the entire string.

--
Paul Lutus
http://www.arachnoid.com

14

Hi --

Pit Capitain wrote:

Paul Lutus schrieb:

Bart Braem wrote:

I will try it with:
string =~ /^\w+\.\w+\z/

But is there a ruby operator to look for matches on the entire string?

string =~ /^\w+\.\w+$/

Must match the entire string. Because of multiline issues, where that is
a factor, you can always split on newlines in advance of this test to be
sure you are matching the entire string unambiguously.

This would be unnecessarily complex.

Not really.

-----------------------------------

#!/usr/bin/ruby

s = "this is\na test\nstring."

a =

a << s.sub(/(^.*$)/,"\\1")

That replaces "this is" with "this is".

a << s.sub(/(^.*\z)/,"\\1")

That replaces "string." with "string.".

a << s.sub(/(^.*$)/m,"\\1")

That replaces "this is\na test\nstring." with "this is\na test\n
string."

a << s.sub(/(^.*\z)/m,"\\1")

That does the same thing as the previous one.

In all of your examples, you're just replacing what was matched with
what was matched. That doesn't tell you anything *about* what was
matched.

Just use Bart's regexp (with \z
instead of $). It matches the entire string.

My point is that, if there are embedded linefeeds and they are an issue,
they must be dealt with. Also, I don't immediately see a difference in
behavior between \z and $, contrary to the documentation's specification
that one matches the end of a line and the other matches the entire string.

You don't see it because you're not looking for it :slight_smile: Look at the
difference in what gets matched:

irb(main):011:0> s =~ /(^.*$)/
=> 0
irb(main):012:0> $1
=> "this is"
irb(main):013:0> s =~ /(^.*\z)/
=> 15
irb(main):014:0> $1
=> "string."
irb(main):015:0> s =~ /(^.*\z)/m
=> 0
irb(main):016:0> $1
=> "this is\na test\nstring."

David

···

On Tue, 19 Sep 2006, Paul Lutus wrote:

--
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails" [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog) [2] | Co-director, Ruby Central, Inc. [4]
[1] Ruby for Rails | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com | [4] http://www.rubycentral.org

15

Paul Lutus wrote:

Also, I don't immediately see a difference in
behavior between \z and $, contrary to the documentation's specification
that one matches the end of a line and the other matches the entire string.

The \z matches up to the terminus of the entire string, including any
newlines that come between. It's different from $ with multiline
because that will match every line end. To see it, change your example
to

a << s.sub(/(^.*$)/,'REPLACE')
a << s.sub(/(^.*\z)/,'REPLACE')
a << s.sub(/(^.*$)/m,'REPLACE')
a << s.sub(/(^.*\z)/m,'REPLACE')

Regards,
Jordan