Getting error as "Can't set variable $`"

Hi, First see the code :

a = ‘foo bar baz 12 34 ret’
b = ‘2.bar foo tree ream baz foo’

match = Regexp.union(a.split(" "))
b.gsub(match) { |m| p m }

>> “bar”

>> “foo”

>> “baz”

>> “foo”

What I am looking for is, for every match inside the block I want to
substitute the $to set to empty string(""`). so that at the end of
gsub I get at last final string “bar foo baz”.

But I am getting error as

a = ‘foo bar baz 12 34 ret’
b = ‘2.bar foo tree ream baz foo’

match = Regexp.union(a.split(" "))

b.gsub(match) { |m| $`=""; m }

~> -:6: Can’t set variable $`

With gsub how can I do that?

Mike S. wrote in post #1136321:

On Feb 11, 2014, at 12:03 AM, Arup R. [email protected] wrote:

Where did the second “foo” go?

If there is a duplicate match, I am interested to take only the first
one. So last “foo” is not desired.

With gsub how can I do that?
I dont understand what you are trying to do. If you want to “ignore” the
stuff which currently ends up in $` you need to match it as gsub
replaces what was matched. For example:

~ ∙ pry
[1] pry(main)> a = ‘foo bar baz 12 34 ret’
=> “foo bar baz 12 34 ret”
[2] pry(main)> token_re = Regexp.union(a.split(" "))
=> /foo|bar|baz|12|34|ret/
[3] pry(main)> b = ‘2.bar foo tree ream baz foo’
=> “2.bar foo tree ream baz foo”
[4] pry(main)> b.gsub(/.*?(#{token_re})/, ‘\1’)
=> “barfoobazfoo”

This makes sense. Just need to remove the last “foo” that’s a challenge.
Also I can put space with some change in the '\1' to ' \1'.

If you just want a list of tokens matched then I wouldn’t use gsub:

[5] pry(main)> b.scan(token_re).join(’ ')
=> “bar foo baz foo”

and if you just want unique tokens matched:

[8] pry(main)> b.scan(token_re).uniq.join(’ ')
=> “bar foo baz”

I know, but this causes performance issue, if you do benchmark, then you
can see. My mistake I didn’t show you that attempt from my side. I wrote
it first, then tried to thinking using gsub.

On Feb 11, 2014, at 12:03 AM, Arup R. [email protected] wrote:

>> “foo”

What I am looking for is, for every match inside the block I want to
substitute the $to set to empty string(""`). so that at the end of
gsub I get at last final string “bar foo baz”.

In the example above you have 4 matches, and you want the final string
to be “bar foo baz”.

Where do the spaces in the final string come from?

Where did the second “foo” go?

With gsub how can I do that?
I dont understand what you are trying to do. If you want to “ignore” the
stuff which currently ends up in $` you need to match it as gsub
replaces what was matched. For example:

~ ∙ pry
[1] pry(main)> a = ‘foo bar baz 12 34 ret’
=> “foo bar baz 12 34 ret”
[2] pry(main)> token_re = Regexp.union(a.split(" "))
=> /foo|bar|baz|12|34|ret/
[3] pry(main)> b = ‘2.bar foo tree ream baz foo’
=> “2.bar foo tree ream baz foo”
[4] pry(main)> b.gsub(/.*?(#{token_re})/, ‘\1’)
=> “barfoobazfoo”

might give you a good starting point, I recommend using rubular.com to
play with regular expressions and reading
http://ruby-doc.org/core-2.1.0/Regexp.html#class-Regexp-label-Repetition
to understand what .*? does.

If you just want a list of tokens matched then I wouldn’t use gsub:

[5] pry(main)> b.scan(token_re).join(’ ')
=> “bar foo baz foo”

and if you just want unique tokens matched:

[8] pry(main)> b.scan(token_re).uniq.join(’ ')
=> “bar foo baz”

Hope this helps,

Mike

Mike S. [email protected]
http://www.stok.ca/~mike/

The “`Stok’ disclaimers” apply.

This forum is not affiliated to the Ruby language, Ruby on Rails framework, nor any Ruby applications discussed here.

| Privacy Policy | Terms of Service | Remote Ruby Jobs