# Gsub("\\\\", "\\\\\\\\") seems unintuitive **URL:** \ **Category:** ruby-talk\ **Created:** [22 February 2008 17:27 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701 "2008-02-22T17:27:44Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![John\_Woods](https://avatars.discourse-cdn.com/v4/letter/j/a88e4f/32.png) [@John\_Woods](https://rubytalk.org/u/John_Woods)\ **Post date:** [22 February 2008 17:27 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/1 "2008-02-22T17:27:44Z")
The following confusing behavior is noted in the pickaxe book (2nd ed) on page 75:    # I would expect two backslashes in the result    \> puts "\\".gsub("\\","\\\\")    \    # I would expect four backslashes in the result    \> puts "\\".gsub("\\","\\\\\\\\")    \\ I can certainly work around it, but it seems unintuitive. Is there a reason why gsub behaves this way? Just curious... ---
**Author:** ![J\_Cooper](https://avatars.discourse-cdn.com/v4/letter/j/3e96dc/32.png) [@J\_Cooper](https://rubytalk.org/u/J_Cooper)\ **Post date:** [22 February 2008 17:37 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/2 "2008-02-22T17:37:49Z")
John Woods wrote: > The following confusing behavior is noted in the pickaxe book (2nd ed) > on page 75: > >    # I would expect two backslashes in the result >    \> puts "\\".gsub("\\","\\\\") >    \ > >    # I would expect four backslashes in the result >    \> puts "\\".gsub("\\","\\\\\\\\") >    \\ > > I can certainly work around it, but it seems unintuitive. Is there a > reason why gsub behaves this way? Just curious... It's not a gsub thing, per se--it's a string thing. Backslashes are used in strings to escape special characters. One such character is a " mark. If you want to write a " mark in the middle of a string, you have to escape it with a backslash: "They call me \"Mellow Yellow\" etc." If you didn't, then the " would signify the end of the string! Similarly, in the example you listed, if you just did: "\" then you end up with a string that ISN'T ended! Because you escaped the next ". So, if you want a literal backslash, you have to escape the backslash too: "\\" It just looks confusing because you are escaping the escape character 馃檪 > **路路路** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![W\_James](https://avatars.discourse-cdn.com/v4/letter/w/e274bd/32.png) [@W\_James](https://rubytalk.org/u/W_James)\ **Post date:** [22 February 2008 17:40 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/3 "2008-02-22T17:40:00Z")
puts "\\".gsub("\\"){"\\\\"} > **路路路** > > On Feb 22, 11:27 am, John Woods \ wrote: > > > The following confusing behavior is noted in the pickaxe book (2nd ed) > > on page 75: > > > >    # I would expect two backslashes in the result > >    \> puts "\\".gsub("\\","\\\\") > >    \ > > > >    # I would expect four backslashes in the result > >    \> puts "\\".gsub("\\","\\\\\\\\") > >    \\ > > > > I can certainly work around it, but it seems unintuitive. Is there a > > reason why gsub behaves this way? Just curious... ---
**Author:** ![Rob\_Biedenharn1](https://avatars.discourse-cdn.com/v4/letter/r/57b2e6/32.png) [@Rob\_Biedenharn1](https://rubytalk.org/u/Rob_Biedenharn1)\ **Post date:** [22 February 2008 17:48 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/4 "2008-02-22T17:48:44Z")
Notwithstanding the earlier responses... Since the replacement string is evaluated 'twice', once as a ruby string literal and then again by gsub to look for group refrences like '\1', you need to provide two levels of escaping for a backslash. \ is "\\" so two of them is "\\\\" and you want gsub to see that so it need to have them escaped: "\\\\\\\\" Whew! Yeah, it's unfortunate, but backslash is doing double-duty here: introducing a group reference to the regular expression and escaping characters in a string literal (just like "\n", but also itself). -Rob Rob Biedenharn [http://agileconsultingllc.com](http://agileconsultingllc.com) Rob@AgileConsultingLLC.com > **路路路** > > On Feb 22, 2008, at 12:27 PM, John Woods wrote: > > > The following confusing behavior is noted in the pickaxe book (2nd ed) on page 75: > > > > # I would expect two backslashes in the result > > \> puts "\\".gsub("\\","\\\\") > > \ > > > > # I would expect four backslashes in the result > > \> puts "\\".gsub("\\","\\\\\\\\") > > \\ > > > > I can certainly work around it, but it seems unintuitive. Is there a reason why gsub behaves this way? Just curious... ---
**Author:** ![Kyle\_Schmitt](https://avatars.discourse-cdn.com/v4/letter/k/9e8a1a/32.png) [@Kyle\_Schmitt](https://rubytalk.org/u/Kyle_Schmitt)\ **Post date:** [22 February 2008 17:53 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/5 "2008-02-22T17:53:38Z")
Just as a side note, this is typical in all real programming languages. C, C++, Java, Perl, sh, etc. I \_believe\_ it's also true in python, lithp/scheme, & (o)caml, but for those I've either not used them, or not used them in so long I'm unsure. Some languages, like vb{[6|script|.net](http://6%7Cscript%7C.net)}, use a doubled quote, but those aren't really proper programing languages 馃槈 --Kyle ---
**Author:** ![John\_Woods](https://avatars.discourse-cdn.com/v4/letter/j/a88e4f/32.png) [@John\_Woods](https://rubytalk.org/u/John_Woods)\ **Post date:** [22 February 2008 18:01 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/6 "2008-02-22T18:01:08Z")
Thanks Rob, that's exactly what I was missing -- the second round of escaping is necessary to make escaped references to regex groups work. > **路路路** > > -----Original Message----- > From: Rob Biedenharn > Sent: 02/22/2008 09:48 AM > > > On Feb 22, 2008, at 12:27 PM, John Woods wrote: > > > > > The following confusing behavior is noted in the pickaxe book (2nd ed) on page 75: > > > > > > # I would expect two backslashes in the result > > > \> puts "\\".gsub("\\","\\\\") > > > \ > > > > > > # I would expect four backslashes in the result > > > \> puts "\\".gsub("\\","\\\\\\\\") > > > \\ > > > > > > I can certainly work around it, but it seems unintuitive. Is there a reason why gsub behaves this way? Just curious... > > > > Notwithstanding the earlier responses... > > > > Since the replacement string is evaluated 'twice', once as a ruby string literal and then again by gsub to look for group refrences like '\1', you need to provide two levels of escaping for a backslash. > > > > \ is "\\" > > so two of them is "\\\\" > > and you want gsub to see that so it need to have them escaped: "\\\\\\\\" > > > > Whew! Yeah, it's unfortunate, but backslash is doing double-duty here: introducing a group reference to the regular expression and escaping characters in a string literal (just like "\n", but also itself). > > > > -Rob > > > > Rob Biedenharn [http://agileconsultingllc.com](http://agileconsultingllc.com) > > Rob@AgileConsultingLLC.com ---
**Author:** ![Joe\_Peck](https://avatars.discourse-cdn.com/v4/letter/j/2bfe46/32.png) [@Joe\_Peck](https://rubytalk.org/u/Joe_Peck)\ **Post date:** [17 December 2008 21:07 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/7 "2008-12-17T21:07:51Z")
I stumbled onto this thread trying to figure out a similar problem... > **路路路** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Joe\_Peck](https://avatars.discourse-cdn.com/v4/letter/j/2bfe46/32.png) [@Joe\_Peck](https://rubytalk.org/u/Joe_Peck)\ **Post date:** [17 December 2008 21:12 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/8 "2008-12-17T21:12:03Z")
Joe Peck wrote: > I stumbled onto this thread trying to figure out a similar problem... Dangit, I didn't mean to post the above message 馃檪 Okay, I need to read a site name (like "joe.com") and put a \ in front of the period (so it would be "joe\.com"). I'm having trouble with this, I can't seem to get only ONE \ in front of the period... > > "joe.com".gsub(/\./, "\\\.") =\> "joe\\.com" > > "joe.com".gsub(/\./, "\\\\.") =\> "joe\\.com" Anyone have a clue what to do? I'm probably missing something simple. > **路路路** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Glen\_Holcomb](https://avatars.discourse-cdn.com/v4/letter/g/ecc23a/32.png) [@Glen\_Holcomb](https://rubytalk.org/u/Glen_Holcomb)\ **Post date:** [17 December 2008 21:20 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/9 "2008-12-17T21:20:47Z")
That's because you are in irb. You are getting what you want try this: puts "joe.com".gsub(/\./, "\\\\.") Actually it might be more readable as gsub('.', '\.') > **路路路** > > On Wed, Dec 17, 2008 at 2:12 PM, Joe Peck \ wrote: > > > Joe Peck wrote: > > \> I stumbled onto this thread trying to figure out a similar problem... > > > > Dangit, I didn't mean to post the above message 馃檪 > > > > Okay, I need to read a site name (like "joe.com") and put a \ in front > > of the period (so it would be "joe\.com"). I'm having trouble with > > this, I can't seem to get only ONE \ in front of the period... > > > > \>\> "joe.com".gsub(/\./, "\\\.") > > =\> "joe\\.com" > > \>\> "joe.com".gsub(/\./, "\\\\.") > > =\> "joe\\.com" > > > > Anyone have a clue what to do? I'm probably missing something simple. > > -- > > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). > > -- > "Hey brother Christian with your high and mighty errand, Your actions speak > so loud, I can't hear a word you're saying." > > -Greg Graffin (Bad Religion) ---
**Author:** ![Todd\_Benson](https://avatars.discourse-cdn.com/v4/letter/t/34f0e0/32.png) [@Todd\_Benson](https://rubytalk.org/u/Todd_Benson)\ **Post date:** [17 December 2008 22:56 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/10 "2008-12-17T22:56:24Z")
You are looking at a string with escaping characters (i.e. what it would look like in double quotes). You can verify this by using #puts or "joe.com".gsub('.', '\.').length. hth, Todd > **路路路** > > On Wed, Dec 17, 2008 at 3:12 PM, Joe Peck \ wrote: > > > Joe Peck wrote: > > > > > I stumbled onto this thread trying to figure out a similar problem... > > > > Dangit, I didn't mean to post the above message 馃檪 > > > > Okay, I need to read a site name (like "joe.com") and put a \ in front > > of the period (so it would be "joe\.com"). I'm having trouble with > > this, I can't seem to get only ONE \ in front of the period... > > > > > > "joe.com".gsub(/\./, "\\\.") > > > > =\> "joe\\.com" > > > > > > "joe.com".gsub(/\./, "\\\\.") > > > > =\> "joe\\.com" > > > > Anyone have a clue what to do? I'm probably missing something simple. ---
**Author:** ![Joe\_Peck](https://avatars.discourse-cdn.com/v4/letter/j/2bfe46/32.png) [@Joe\_Peck](https://rubytalk.org/u/Joe_Peck)\ **Post date:** [18 December 2008 15:12 UTC](https://rubytalk.org/t/gsub-seems-unintuitive/44701/11 "2008-12-18T15:12:51Z")
Okay, those last two explanations helped clear up my confusion. Thanks. > **路路路** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).