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comp.lang.ruby

Scanning a String

basi

4/28/2005 1:42:00 AM

Hello,
How do I scan a string for a pattern and process it when found? For
example:

for all occurrences of two vowel letters in succession, insert the
apostrophe between the vowels.

Thus:

breakground > bre'akgro'und

thank you for your help!
basi
11 Answers

Nicholas Seckar

4/28/2005 2:04:00 AM

0

On 4/27/05, basi <basiibarra@yahoo.com> wrote:
> Hello,
> How do I scan a string for a pattern and process it when found? For
> example:
>
> for all occurrences of two vowel letters in succession, insert the
> apostrophe between the vowels.

some_string.gsub(/([aeiou])([aeiou])/) {|match| $1 + "'" + $2}

dblack

4/28/2005 2:11:00 AM

0

basi

4/28/2005 2:30:00 AM

0

David,
Yes, three vowels in a row should be handled as you indicated.
Thank you, and to Nicholas Seckar as well, for the quick reply.

I think I should finally bite the bullet and learn regex.

Basi

Nicholas Seckar

4/28/2005 2:40:00 AM

0

On 4/27/05, David A. Black <dblack@wobblini.net> wrote:
> (You don't really need the block arg (match) :-)

Good point :-)

> pious".gsub(/([aeiou])(?=[aeiou])/) { "#{$1}'#{$2}" }

We could also do away with the block altogether and use
"pious".gsub(/([aeiou])(?=[aeiou])/, '\1\'\2')

Although I don't know if one approach is preferred to the other.

Robert Klemme

4/28/2005 7:27:00 AM

0


"Nicholas Seckar" <nseckar@gmail.com> schrieb im Newsbeitrag
news:6bfb9c8a050427193967475977@mail.gmail.com...
> On 4/27/05, David A. Black <dblack@wobblini.net> wrote:
> > (You don't really need the block arg (match) :-)
>
> Good point :-)
>
> > pious".gsub(/([aeiou])(?=[aeiou])/) { "#{$1}'#{$2}" }
>
> We could also do away with the block altogether and use
> "pious".gsub(/([aeiou])(?=[aeiou])/, '\1\'\2')
>
> Although I don't know if one approach is preferred to the other.

Yes, it's preferred because it's faster. Although your variant works, I
usually prefer to put the correct number of backslashes in there:

"pious".gsub(/([aeiou])(?=[aeiou])/, '\\1\'\\2')

Kind regards

robert

dblack

4/28/2005 10:21:00 AM

0

dblack

4/28/2005 10:22:00 AM

0

Robert Klemme

4/28/2005 10:53:00 AM

0


"David A. Black" <dblack@wobblini.net> schrieb im Newsbeitrag
news:Pine.LNX.4.61.0504280320190.13336@wobblini...
> Hi --
>
> On Thu, 28 Apr 2005, Robert Klemme wrote:
>
> >
> > "Nicholas Seckar" <nseckar@gmail.com> schrieb im Newsbeitrag
> > news:6bfb9c8a050427193967475977@mail.gmail.com...
> >> On 4/27/05, David A. Black <dblack@wobblini.net> wrote:
> >>> (You don't really need the block arg (match) :-)
> >>
> >> Good point :-)
> >>
> >>> pious".gsub(/([aeiou])(?=[aeiou])/) { "#{$1}'#{$2}" }
> >>
> >> We could also do away with the block altogether and use
> >> "pious".gsub(/([aeiou])(?=[aeiou])/, '\1\'\2')
> >>
> >> Although I don't know if one approach is preferred to the other.
> >
> > Yes, it's preferred because it's faster. Although your variant works,
I
> > usually prefer to put the correct number of backslashes in there:
> >
> > "pious".gsub(/([aeiou])(?=[aeiou])/, '\\1\'\\2')
>
> Why do you consider that more correct?

Although both produce the same:

>> p '\1'
"\\1"
=> nil
>> p '\\1'
"\\1"
=> nil

because Ruby is so kind to take "\1" literally (i.e not using the
backslash as escaping char because "\1" is not an escaping sequence). I
prefer to explicitely escape the backslash and put the "1" in there
literally. IMHO it's more fail safe when changes are done (especially
when changing single quotes to double quotes, see below).

Consider also

>> p "\n"
"\n"
=> nil
>> p "\\n"
"\\n"
=> nil

>> p "\1"
"\001"
=> nil
>> p "\\1"
"\\1"
=> nil

Might be overly cautious but this is the kind of error that bites you and
if you're not lucky it can take quite some time to figure what's going on
here.

Kind regards

robert

dblack

4/28/2005 12:13:00 PM

0

Robert Klemme

4/28/2005 12:27:00 PM

0


"David A. Black" <dblack@wobblini.net> schrieb im Newsbeitrag
news:Pine.LNX.4.61.0504280509220.30582@wobblini...
> Hi --
>
> On Thu, 28 Apr 2005, Robert Klemme wrote:
>
> >
> > "David A. Black" <dblack@wobblini.net> schrieb im Newsbeitrag
> > news:Pine.LNX.4.61.0504280320190.13336@wobblini...
> >> Hi --
> >>
> >> On Thu, 28 Apr 2005, Robert Klemme wrote:
> >>> Yes, it's preferred because it's faster. Although your variant
works,
> > I
> >>> usually prefer to put the correct number of backslashes in there:
> >>>
> >>> "pious".gsub(/([aeiou])(?=[aeiou])/, '\\1\'\\2')
> >>
> >> Why do you consider that more correct?
> >
> > Although both produce the same:
> >
> >>> p '\1'
> > "\\1"
> > => nil
> >>> p '\\1'
> > "\\1"
> > => nil
> >
> > because Ruby is so kind to take "\1" literally (i.e not using the
> > backslash as escaping char because "\1" is not an escaping sequence).
I
> > prefer to explicitely escape the backslash and put the "1" in there
> > literally. IMHO it's more fail safe when changes are done (especially
> > when changing single quotes to double quotes, see below).
>
> If you're talking about double quotes then clearly it has to be "\\1".
> I meant specifically in the case of single quotes.

Well, yes. But quotes don't necessarily stay single through the course of
a software's lifecycle - with all this dating and matching around... :-)
Sorry, drifting off-topic.

> Anyway, it's not a
> big deal -- I was just curious.

Thought so. I hope I could satisfy your curiosity. :-)

Kind regards

robert