Regexp: named captures

Ruby
1

How do named captures in Ruby work? This is what I’ve tried:

irb(main):001:0> if /(?.+)/ =~ /ari/
irb(main):002:1> puts $name
irb(main):003:1> end
SyntaxError: compile error
(irb):1: undefined (?..) sequence: /(?.+)/
from (irb):3

and if I do this:

irb(main):007:0> if /(.+)/ =~ /ari/
irb(main):008:1> puts $name
irb(main):009:1> end
TypeError: can’t convert Regexp into String
from (irb):7

I get a Regexp => String error.

Bwah?
aRi
-------------------------------------------|
Nietzsche is my copilot

2

Ruby doesn’t have named-captures.

Coming from .NET myself, at first I was dissapointed. Eventually I
grew to love the simplicity of $1, $2, etc, but that’s just me. :slight_smile:

3

Hi –

On Tue, 21 Aug 2007, Sam S. wrote:

Ruby doesn’t have named-captures.

The new regex engine, Oniguruma, does. You can install it in 1.8, and
it’s included in 1.9/2.0.

David

4

Ari B. pisze:

How do named captures in Ruby work? This is what I’ve tried:

irb(main):001:0> if /(?.+)/ =~ /ari/
irb(main):002:1> puts $name
irb(main):003:1> end

1.9 supports that (so will 2.0):

if match = /(?blah)/.match(“blah”)
puts match[“name”]
end

lopex

5

On Aug 20, 3:32 pm, William J. [email protected] wrote:

On Aug 20, 2:44 pm, Ari B. [email protected] wrote:

How do named captures in Ruby work? This is what I’ve tried:

A work-around:

md = “foo bar”.match( /(\w+) (\w+)/ )
==>#MatchData:0x2851ef0
name, surname = md.captures
==>[“foo”, “bar”]
name
==>“foo”
surname
==>“bar”

Or my favorite (courtesy of Ara):

_, name, surname = /(\w+) (\w+)/.match(“foo bar”).to_a

6

On Aug 20, 2:44 pm, Ari B. [email protected] wrote:

-------------------------------------------|
Nietzsche is my copilot

A work-around:

md = “foo bar”.match( /(\w+) (\w+)/ )
==>#MatchData:0x2851ef0
name, surname = md.captures
==>[“foo”, “bar”]
name
==>“foo”
surname
==>“bar”

7

On Aug 20, 4:40 pm, Phrogz [email protected] wrote:

name
==>“foo”
surname
==>“bar”

Or my favorite (courtesy of Ara):

_, name, surname = /(\w+) (\w+)/.match(“foo bar”).to_a

name, surname = /(\w+) (\w+)/.match(“foo bar”).captures

8

On Aug 20, 2007, at 4:13 PM, David A. Black wrote:

On Tue, 21 Aug 2007, Sam S. wrote:

Ruby doesn’t have named-captures.

The new regex engine, Oniguruma, does. You can install it in 1.8, and
it’s included in 1.9/2.0.

I’ve read about Oniguruma - is it just a different engine behind
class Regex, and it won’t change the syntax, right?

Because there’s a Regexp wrapper I’m writing (with much help from
Robert K.) that uses Regex as the base, and all of the current
syntax.

~ Ari
English is like a pseudo-random number generator - there are a
bajillion rules to it, but nobody cares.

9

Hi –

On Tue, 21 Aug 2007, William J. wrote:

==>["foo", "bar"]

name
==>“foo”
surname
==>“bar”

Or my favorite (courtesy of Ara):

_, name, surname = /(\w+) (\w+)/.match(“foo bar”).to_a

name, surname = /(\w+) (\w+)/.match(“foo bar”).captures

That has the disadvantage that it will blow up if the match fails (no
captures method for nil).

David

10

Hi,

I need some help in simplefying my life

I need to create lots of tables from arrays and I need to provide

each of the columns with a heading. For eample, I have

two headings “a-value” and “b-value” specified as follows:

a = [“a-value”, “b-value”]
b = [10, 10]

The array b contains the width of the field, so that I get:

a-value b-value

Two ways to do this are as follows:

puts “#{‘a-value’.rjust(10)}#{‘b-value’.rjust(10)}”
puts “#{a[0].rjust(b[0])}#{a[1].rjust(b[1])}”

which is difficult to debug, so that I’m looking for

a simpler process, specificaly by writing a function.

The following one works:

def heading2(x, n)
x.length.times do |i|
print “#{x[i].rjust(n[i])}”
end
print “\n\n”
end

puts
heading2(a,b)

But this approach doesn’t. Why not? Are there other ways to make

this simpler?

def heading1(x, n)
s = “”
x.length.times do |i|
s = s + “#{’” + x[i] + “’.rjust(” + n[i].to_s + “)}”
end
p s
print s
puts s
return s
end

heading1(a,b)
puts “#{heading1(a, b)}”
puts “”#{heading1(a, b)}""

Thanks ahead. (NOTE: This file can be run from TextMate)

Peter V.
[email protected]

11

Hi Peter.

On 22 Aug 2007, at 12:21, Peter V. wrote:

But this approach doesn’t. Why not? Are there other ways to make

this simpler?

Maybe I’ve got the wrong end of the stick on this, but I get it to
work like this:

==========================

a = [“a-value”,“b-value”, “c-value”]
b = [10,30,15]

def header(names, widths)
header = ‘’
names.each_with_index do |v,i|
header += v.rjust widths[i]
end
header
end

p header(a, b)

==========================

Hope this helps.

Douglas F Shearer
[email protected]

12

Peter V. wrote:

But this approach doesn’t. Why not? Are there other ways to make

this simpler?

Here’s an idea that’s simpler … if you already have all the tools in
place.

Push your raw data into XML. Write an XSLT that converts it to XHTML.
Pipe this thru lynx -dump.

No joke: I have done that to produce beautiful automated text-only
e-mails, containing tables of data.

13

Ruby Reports. Ruport. Check it out.

On Aug 22, 2007, at 7:21 AM, Peter V. wrote:

Two ways to do this are as follows:

end
s = “”
puts “#{heading1(a, b)}”

---------------------------------------------------------------|
~Ari
“I don’t suffer from insanity. I enjoy every minute of it” --1337est
man alive

14

How about using “rescue nil” ?

ruby -e ‘name, surname = /(\w+) (\w+)/.match(“foo bar”).captures rescue
nil; p name, surname’
=> “foo”
=> “bar”

ruby -e ‘name, surname = /(\w+) (\w+)/.match("").captures rescue nil; p
name, surname’
=> nil
=> nil

Cheers,

j.k.

15

Douglas,

Thanks, this works also. The result is put in a string and the
string is printed.

I guess what I was trying to do is to create a string that ruby is
supposed to interpret, or execute. Perhaps there is another command
to accomplish this.

Peter

16

Ari,

Had not come across Ruport. Sounds interesting, especially since I
have to do a lot of reporting. I will investigate further.

Thanks,

Peter

17

On Aug 20, 5:17 pm, Ari B. [email protected] wrote:

current regexp engine to barf. Do you mean syntax inside the regex? Or
the syntax for declaring a regex? Or are you interested only in
backwards compatibility?

So yea, just backwards compatibility.

Is Oniguruma behind a new class Oniguruma.new or behind Regexp.new

Sorry, but I can’t seem to find much documentation on it.

I believe that under 1.8 it comes as its own class, but in 1.9 on it
is the code behind the builtin Regexp class. (I could be wrong,
though. There may be a way to build 1.8 using Oniguruma as the basis
for Regexp.)

And, from what I know, all regex features available in 1.8 use the
same syntax in Oniguruma.

18

On Aug 20, 4:00 pm, Ari B. [email protected] wrote:

I’ve read about Oniguruma - is it just a different engine behind
class Regex, and it won’t change the syntax, right?

Because there’s a Regexp wrapper I’m writing (with much help from
Robert K.) that uses Regex as the base, and all of the current
syntax.

What do you mean by “change the syntax”?

For example, Oniguruma supports named captures (per this thread) and
zero-width negative lookbehind assertions, and … more.

Certainly the syntax is different for new features, which cause the
current regexp engine to barf. Do you mean syntax inside the regex? Or
the syntax for declaring a regex? Or are you interested only in
backwards compatibility?

19

Philip,

That sounds complicated, given my current state of knowledge of Ruby,
but thanks for the recommendation

Peter

20

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