# Substituting variables in a method **URL:** \ **Category:** Ruby\ **Created:** [May 23, 2007, 1:50am UTC](https://www.ruby-forum.com/t/substituting-variables-in-a-method/104829 "2007-05-23T01:50:47Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Michael\_WSRyder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/53a042/32.png) [@Michael\_WSRyder](https://www.ruby-forum.com/u/Michael_WSRyder)\ **Post date:** [May 23, 2007, 1:50am UTC](https://www.ruby-forum.com/t/substituting-variables-in-a-method/104829/1 "2007-05-23T01:50:47Z")
I am trying to figure out how to pass variables for the parameters to a method. I want to do something like b = a.tr({c}, {d}) where ‘c’ is the text to be matched and ‘d’ is the replacement text. Obviously the above does not work, nor does b = a.tr(#{c}, ${d}). Is this even possible or do I need to work out some regular expression to do the same thing. What I am trying to do is have a method where I can say change all periods to commas and commas to periods or change all \*s to #s or … ---
**Author:** ![Michael\_WSRyder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/53a042/32.png) [@Michael\_WSRyder](https://www.ruby-forum.com/u/Michael_WSRyder)\ **Post date:** [May 23, 2007, 2:26am UTC](https://www.ruby-forum.com/t/substituting-variables-in-a-method/104829/2 "2007-05-23T02:26:49Z")
On 5/23/07, Michael W. Ryder [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I am trying to figure out how to pass variables for the parameters to a > method. I want to do something like b = a.tr({c}, {d}) where ‘c’ is the > text to be matched and ‘d’ is the replacement text. Obviously the above > does not work, nor does b = a.tr(#{c}, ${d}). Is this even possible or > do I need to work out some regular expression to do the same thing. > What I am trying to do is have a method where I can say change all > periods to commas and commas to periods or change all \*s to #s or … I’m not sure if this is what you want, but… str1 = "I am a string. " str2 = "You are not. " str3 = str1 + str2 str4 = str3.gsub(“#{str1}”,“#{str2}”) p str1 p str2 p str3 p str4 Harry – A Look into Japanese Ruby List in English [http://www.kakueki.com/](http://www.kakueki.com/) ---
**Author:** ![Michael\_WSRyder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/53a042/32.png) [@Michael\_WSRyder](https://www.ruby-forum.com/u/Michael_WSRyder)\ **Post date:** [May 23, 2007, 3:10am UTC](https://www.ruby-forum.com/t/substituting-variables-in-a-method/104829/3 "2007-05-23T03:10:51Z")
Harry K. wrote: > p str3 > p str4 > > Harry That’s what I was looking for. I would never have thought of enclosing the variables in double quotes. It also works for the .tr method. Is there some place that describes how to do these types of things or is it just a matter of experimenting or asking others? ---
**Author:** ![Michael\_WSRyder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/53a042/32.png) [@Michael\_WSRyder](https://www.ruby-forum.com/u/Michael_WSRyder)\ **Post date:** [May 23, 2007, 3:45am UTC](https://www.ruby-forum.com/t/substituting-variables-in-a-method/104829/4 "2007-05-23T03:45:54Z")
Rick DeNatale wrote: > On 5/22/07, Harry K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > str4 = str3.gsub(“#{str1}”,“#{str2}”) > > The string interpolation is completely unnecessary, this is the same as: > str4 = str3.gsub(str1, str2) How does one know when to use string interpolation and when it isn’t needed? I know that if I want to put a variable in the middle of a string I have to use interpolation so I thought I also needed something like that in this case as I didn’t want to convert c’s to d’s. ---
**Author:** ![Michael\_WSRyder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/53a042/32.png) [@Michael\_WSRyder](https://www.ruby-forum.com/u/Michael_WSRyder)\ **Post date:** [May 23, 2007, 3:27am UTC](https://www.ruby-forum.com/t/substituting-variables-in-a-method/104829/5 "2007-05-23T03:27:52Z")
On 5/22/07, Harry K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > str4 = str3.gsub(“#{str1}”,“#{str2}”) The string interpolation is completely unnecessary, this is the same as: str4 = str3.gsub(str1, str2) – Rick DeNatale My blog on Ruby [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) ---
**Author:** ![Michael\_WSRyder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/53a042/32.png) [@Michael\_WSRyder](https://www.ruby-forum.com/u/Michael_WSRyder)\ **Post date:** [May 23, 2007, 4:35am UTC](https://www.ruby-forum.com/t/substituting-variables-in-a-method/104829/6 "2007-05-23T04:35:58Z")
On 5/23/07, Michael W. Ryder [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > needed? I know that if I want to put a variable in the middle of a > string I have to use interpolation so I thought I also needed something > like that in this case as I didn’t want to convert c’s to d’s. OK, I gave a bad example. Maybe this is a little better. str1 = "str1 string. " str2 = “more stuff” str3 = str1.gsub(str1,str2) str4 = str1.gsub(“str1”,“str2”) str5 = str1.gsub(“str1”,“Now #{str2}”) p str1 p str2 p str3 p str4 p str5 Harry – A Look into Japanese Ruby List in English [http://www.kakueki.com/](http://www.kakueki.com/) ---
**Author:** ![Michael\_WSRyder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/53a042/32.png) [@Michael\_WSRyder](https://www.ruby-forum.com/u/Michael_WSRyder)\ **Post date:** [May 23, 2007, 6:40am UTC](https://www.ruby-forum.com/t/substituting-variables-in-a-method/104829/7 "2007-05-23T06:40:07Z")
In message [pYM4i.345947$removed\_email\_address@domain.invalid](mailto:pYM4i.345947$removed_email_address@domain.invalid), “Michael W. Ryder” writes: > How does one know when to use string interpolation and when it isn’t > needed? I know that if I want to put a variable in the middle of a > string I have to use interpolation so I thought I also needed something > like that in this case as I didn’t want to convert c’s to d’s. It’s simple. If you are trying to embed a variable in a literal string, you need string interpolation. That’s it. That’s the only time you need it. -s ---
**Author:** ![Michael\_WSRyder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/53a042/32.png) [@Michael\_WSRyder](https://www.ruby-forum.com/u/Michael_WSRyder)\ **Post date:** [May 23, 2007, 7:16am UTC](https://www.ruby-forum.com/t/substituting-variables-in-a-method/104829/8 "2007-05-23T07:16:08Z")
Harry K. wrote: > > > > > str1 = "str1 string. " > > Harry It took me a couple of minutes to figure out what these were doing and they do make some of it clearer. What you helped me to figure out was how to do something like: a = “This is a test!” c = “!” d = “.” b = a.gsub(c, d) puts b I didn’t want to convert c’s to d’s in this example, but wanted to convert the exclamation mark to a period and get ‘This is a test.’. I can also change c to “test” and d to “mess” to get ‘This is a mess!’. Thank you and Rick for the assistance.