Finding un-escaped characters in scan()

ruby-talk
1

I have a string that looks like this: "test,\,test". And I'm trying to
count the commas which don't follow a \. But when using scan(/[^\\],/) it
only finds the first comma. I think this is because after scan() has found a
comma without a backslash, it continues from where it left off, and since
there's no character before the next comma, it won't match it. Does anyone
know how to fix it?

2

I don't see that behaviour:

irb(main):001:0> "test,\,test,test2,\,test3".scan(/[^\\],/)
=> ["t,", ",", "t,", "2,"]
irb(main):002:0>

4 total, as expected.

···

-----Original Message-----
From: Fred Phillips [mailto:fophillips1990@gmail.com]
Sent: Saturday, July 28, 2007 6:03 AM
To: ruby-talk ML
Subject: Finding un-escaped characters in scan()

I have a string that looks like this: "test,\,test". And I'm
trying to count the commas which don't follow a \. But when
using scan(/[^\\],/) it only finds the first comma. I think
this is because after scan() has found a comma without a
backslash, it continues from where it left off, and since
there's no character before the next comma, it won't match
it. Does anyone know how to fix it?

3

Works for me:

irb(main):001:0> "test,\,test".scan(/[^\\],/)
=> ["t,", ","]

Todd

···

On 7/28/07, Fred Phillips <fophillips1990@gmail.com> wrote:

I have a string that looks like this: "test,\,test". And I'm trying to
count the commas which don't follow a \. But when using scan(/[^\\],/) it
only finds the first comma. I think this is because after scan() has found a
comma without a backslash, it continues from where it left off, and since
there's no character before the next comma, it won't match it. Does anyone
know how to fix it?

4

Fred Phillips wrote:

I have a string that looks like this: "test,\,test". And I'm trying to
count the commas which don't follow a \. But when using scan(/[^\\],/)
it
only finds the first comma. I think this is because after scan() has
found a
comma without a backslash, it continues from where it left off, and
since
there's no character before the next comma, it won't match it. Does
anyone
know how to fix it?

Just wanted to point out a mistake the OP and all of the replying people
made:
",\," # => ","
The , is *not* escaped. You need ',\,' # => ',\\,'

Regards
Stefan

···

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5

Are you expecting something like this,

str = "test,test"
p str.scan(/,/) #[","]

to give you [",",","] ?

Harry

···

On 7/28/07, Fred Phillips <fophillips1990@gmail.com> wrote:

I have a string that looks like this: "test,\,test". And I'm trying to
count the commas which don't follow a \. But when using scan(/[^\\],/) it
only finds the first comma. I think this is because after scan() has found a
comma without a backslash, it continues from where it left off, and since
there's no character before the next comma, it won't match it. Does anyone
know how to fix it?

--
A Look into Japanese Ruby List in English

6

Fred Phillips wrote:

I have a string that looks like this: "test,\,test". And I'm trying to
count the commas which don't follow a \. But when using scan(/[^\\],/)
it
only finds the first comma. I think this is because after scan() has
found a
comma without a backslash, it continues from where it left off, and
since
there's no character before the next comma, it won't match it. Does
anyone
know how to fix it?

If you can use Ruby 1.9, you simly can express it using 'negative look
behind':

irb(main):001:0> "test,\\,test".scan(/(?<!\\),/)
=> [",", ","]
irb(main):002:0> "test,\\,test,test2,\\,test3".scan(/(?<!\\),/)
=> [",", ",", ",", ","]

Wolfgang Nádasi-Donner

···

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Posted via http://www.ruby-forum.com/\.

7

Hmm, it appears I made a typo in my actual code. But this still isn't the
result I want.

For instance "test,test" only returns one comma. And the results you have
shown above, are returning the wrong number as well.

8

If so,
here is one way.
There is probably a more elegant way.

require 'enumerator'
str = "test,\\,\\,"
str.split(//).each_cons(2){|x|p x[1] if x[0] != "\\" and x[1] == ","}

Harry

···

On 7/28/07, Harry Kakueki <list.push@gmail.com> wrote:

On 7/28/07, Fred Phillips <fophillips1990@gmail.com> wrote:
> I have a string that looks like this: "test,\,test". And I'm trying to
> count the commas which don't follow a \. But when using scan(/[^\\],/) it
> only finds the first comma. I think this is because after scan() has found a
> comma without a backslash, it continues from where it left off, and since
> there's no character before the next comma, it won't match it. Does anyone
> know how to fix it?
>
Are you expecting something like this,

str = "test,test"
p str.scan(/,/) #[","]

to give you [",",","] ?

Harry

--
A Look into Japanese Ruby List in English

9

Fred:

Ah, I see what you are saying in your original post.

"test,test".scan(/.,/)
=> ["t,"]

It should find "," too, right?

Interesting behavior and has nothing to do with backslashes, just the
fact that scan won't find it if the character is adjacent to itself.
Like you said, where it starts the next scan, maybe. I'm not sure how
to get around it without playing around a bit.

Todd

···

On 7/28/07, Fred Phillips <fophillips1990@gmail.com> wrote:

Hmm, it appears I made a typo in my actual code. But this still isn't the
result I want.

For instance "test,test" only returns one comma. And the results you have
shown above, are returning the wrong number as well.

10

Excellent, that works like a charm. Thanks.

···

On 28/07/07, Harry Kakueki <list.push@gmail.com> wrote:

On 7/28/07, Harry Kakueki <list.push@gmail.com> wrote:
> On 7/28/07, Fred Phillips <fophillips1990@gmail.com> wrote:
> > I have a string that looks like this: "test,\,test". And I'm trying
to
> > count the commas which don't follow a \. But when using scan(/[^\\],/)
it
> > only finds the first comma. I think this is because after scan() has
found a
> > comma without a backslash, it continues from where it left off, and
since
> > there's no character before the next comma, it won't match it. Does
anyone
> > know how to fix it?
> >
> Are you expecting something like this,
>
> str = "test,test"
> p str.scan(/,/) #[","]
>
> to give you [",",","] ?
>
> Harry

If so,
here is one way.
There is probably a more elegant way.

require 'enumerator'
str = "test,\\,\\,"
str.split(//).each_cons(2){|x|p x[1] if x[0] != "\\" and x[1] == ","}

Harry

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