Newbie : Regular expression

Ruby
1

Hi,

Can some one please tell me of an example expression which maps to this
regex

“(^#{r}$)”

The ruby statement is

regex = Regexp.new("(^#{r}$)")

2

r = ‘hello’
str = ‘hello’

if Regexp.new(“(^#{r}$)”).match str
puts “Yep”
puts $1
end

–output:–
Yep
hello

Try practicing here:

3

7stud – wrote in post #1081740:

r = ‘hello’
str = ‘hello’

if Regexp.new("(^#{r}$)").match str
puts “Yep”
puts $1
end

–output:–
Yep
hello

Thanks for the prompt reply. Can you explain a bit about #{r}. What that
means ??

4

greeting = ‘hello’
str = “#{greeting} world”

puts str

–output:–
hello world

It’s called ‘string interpolation’. It’s used to insert the value of a
variable (or an expression) into a string.

5

On Oct 28, 2012, at 18:14 , Muhammad S. [email protected]
wrote:

Hi,

Can some one please tell me of an example expression which maps to this
regex

“(^#{r}$)”

The ruby statement is

regex = Regexp.new(“(^#{r}$)”)

it is entirely dependent on what r evaluates to… so no, we can’t
really.

6

Hi Muhammad,

That depends entirely on what the value of “r” is. The #{} is
interpolation, like in strings.

e.g.

r = /boo/
regexp = Regexp.new("(^#{r}$)")

regexp is now /(^(?-mix:boo)$)/, which is basically the same as saying
/(^(?:boo)$)/, … which is basically the same as /(^boo$)/ in this
context.

In other words, the value of “r” gets included there, with any options
on the regexp “r” set. If “r” is a String, its value is included
verbatim, as if it was part of the regexp source.

Cheers,

Arlen