Gsub wrapper

Ruby
1

Help!

How do I get $1, $2, and $3 to get interpolated in the following
snippet?

string = ‘This is a test of the emergency’
regexp = Regexp.new(’(\W)+(\w\w)(\W)+’)
replacement = ‘$1->$2<-$3’
user_wants_upcase=FALSE

Note: All variables above are set by the user of the program, so I

don’t know

what they will contain before runtime.

string.gsub!(regexp) {
return_value = string # Here, how do I get $1, $2, and $3 to
interpolate?

if (user_wants_uppercase)
return_value.upcase! || return_value
end

return_value
}

I want return_value to be -> ‘This ->is<- a test ->of<- the emergency’

Note: I know that I can get it to work with the non-block version of
gsub! but I need to use the block version.

Thanks

Hector

2

Hector wrote:

Help!

How do I get $1, $2, and $3 to get interpolated in the following
snippet?

string = ‘This is a test of the emergency’
regexp = Regexp.new(’(\W)+(\w\w)(\W)+’)
replacement = ‘$1->$2<-$3’

If you have ‘"#{$1}->#{$2}<-#{$3}"’, you can eval
it in the block. This is probably a bad idea, though.

To make this a bit safer, you would probably want the
user to give you some kind of a sprintf-style string
that you format inside the block. This might limit
the user to strictly linear numbering or something.

user_wants_upcase=FALSE

Note: All variables above are set by the user of the program, so I

don’t know

what they will contain before runtime.

string.gsub!(regexp) {
return_value = string # Here, how do I get $1, $2, and $3 to
interpolate?

if (user_wants_uppercase)
return_value.upcase! || return_value
end

return_value
}

I want return_value to be -> ‘This ->is<- a test ->of<- the emergency’

Note: I know that I can get it to work with the non-block version of
gsub! but I need to use the block version.

Thanks

Hector

E

3

On Mar 2, 2006, at 6:09 PM, Hector wrote:

Note: All variables above are set by the user of the program, so I

Hector

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

assuming I understand your question:

str = “#{$1}->#{$2}<-#{$3}”

Alternatively:

str = “#$1->#$2<-#$3”

4

Timothy G. wrote:

str = “We love Ruby”
puts str.gsub(/We (\w+) \w+/, ‘Why do we \1 it?’)
puts str.gsub(/(\w+)$/, “it because \1 allows us to do cool stuff!”)

First, thanks to everyone for your input.

But I wanted to be able to invoke ‘gsub’ with end-user specified strings
for both the regex pattern and the replacement string. If the end-user
regex patern contains regexp groupings and the replacement string
contains any of $1, $2, … $9, these variables($1,$2…) will not get
interpolated because they are within a string object. The non-block
version of gsub works fine but I need more flexibility.

Maybe a sample invokation of the script would help explain what I want.
Here’s a sample:

INPUT_STRING = ‘This is getting to be a bear!’
script invokation -> snr.rb -regex’(\W)+(\w\w)(\W)+’
-replacement’$1->$2<-$3’

Should display -> ‘This ->is<- getting ->to<- ->be<- a bear!’

I’m finding it hard to explain exactly what it is I am looking for -
simple concept but difficult for me to explain.

Again, thank you for your help.

Hector

5

Hector wrote:

Note: All variables above are set by the user of the program, so I

return_value
}

I want return_value to be -> ‘This ->is<- a test ->of<- the emergency’

Note: I know that I can get it to work with the non-block version of
gsub! but I need to use the block version.

In your case you don’t even need groups, because you can nicely anchor
the
expression on word boundaries:

upcase=true
=> true

‘This is a test of the emergency’.gsub(/\b\w\w\b/) {|m| “->” << (upcase
? m.upcase : m) << “<-”}
=> “This ->IS<- a test ->OF<- the emergency”

Otherwise

‘This is a test of the emergency’.gsub(/(\W)+(\w\w)(\W)+/) {|m|
“#$1->#{upcase ? $2.upcase : $2}<-#$3”}
=> “This ->IS<- a test ->OF<- the emergency”

Note: #$1 in a double quoted string is a shortcut for #{$1}.

Kind regards

robert
6

$1 is a global variable which is set to the value matched by the
bracketed bits. You just treat it like any string.

e.g. “The first parameter was #$1” or number = $2.to_f

In gsub substitutions the letters ‘\N’ in the substitution text, where
N is a number from 1 to 9, will be replaced by the substituted
sequence. If you use double quotes, you will need two backslashes
because this is not a normal escape sequence.

str = “We love Ruby”
puts str.gsub(/We (\w+) \w+/, ‘Why do we \1 it?’)
puts str.gsub(/(\w+)$/, “it because \1 allows us to do cool stuff!”)