Backslashes in gsub (escaping and backreferencing)

Posted by polygenelubricants on Stack Overflow See other posts from Stack Overflow or by polygenelubricants
Published on 2010-06-12T11:48:07Z Indexed on 2010/06/12 11:52 UTC
Read the original article Hit count: 318

Filed under:

ruby

|

regex

|

replace

|

escape-sequence

|

backreference

Consider the following snippet:

puts 'hello'.gsub(/.+/, '\0 \\0 \\\0 \\\\0')

This prints (as seen on ideone.com):

hello hello \0 \0

This was very surprising, because I'd expect to see something like this instead:

hello \0 \hello \\0

My argument is that \ is an escape character, so you write \\ to get a literal backslash, thus \\0 is a literal backslash \ followed by 0, etc. Obviously this is not how gsub is interpreting it, so can someone explain what's going on?

And what do I have to do to get the replacement I want above?

© Stack Overflow or respective owner

Related posts about ruby

Setting up Rails to work with sqlserver

as seen on Stack Overflow - Search for 'Stack Overflow'
Ok I followed the steps for setting up ruby and rails on my Vista machine and I am having a problem connecting to the database. Contents of database.yml development: adapter: sqlserver database: APPS_SETUP Host: WindowsVT06\SQLEXPRESS Username: se Password: paswd Run rake db:migrate… >>> More
marshal data too short!!!

as seen on Stack Overflow - Search for 'Stack Overflow'
My application requires to keep large data objects in session. There are like 3-4 data objects each created by parsing a csv containing 150 X 20 cells having strings of 3-4 characters. My application shows this error- "marshal data too short". I tried this- Deleting the old session table. Deleting… >>> More
Sinatra and XML POST request

as seen on Stack Overflow - Search for 'Stack Overflow'
I don't know is it my mistake or no. So i have that code: <code> post '/singin/get_token' do content_type :xml puts request.body.read puts xmlRequest xmlRequest = REXML::Document.new(request.body.read) ... </code> And when i post something like that: <code> <?xml… >>> More
how to change ruby path from /usr/bin/ruby to /usr/local/bin/ruby

as seen on Stack Overflow - Search for 'Stack Overflow'
reading around the various ruby install tutorials it's required to change path from /usr/bin/ruby to /usr/local/bin/ruby but i cant seem to be able to do it. Ultimately i want to install Ruby 1.9.2, should i uninstall 1.8.7 or what? i tried to install Ruby 1.9.2 with macports, the installation seemed… >>> More
strange bundler error: tar_input.rb:49:in `initialize': not in gzip format (Zlib::GzipFile::Error) o

as seen on Stack Overflow - Search for 'Stack Overflow'
i am getting a strange bundler error when running bundle pack with bundler 0.9.12 any ideas? (see pastie for a better formatted code: http://pastie.org/881328 ) /opt/ruby-enterprise-1.8.7-2010.01/lib/ruby/site_ruby/1.8/rubygems/package/tar_input.rb:49:in `initialize': not in gzip format (Zlib::GzipFile::Error) … >>> More

Related posts about regex

Find multiple regex in each line and skip result if one of the regex doesn't match

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a list of variables: variables = ['VariableA', 'VariableB','VariableC'] which I'm going to search for, line by line ifile = open("temp.txt",'r') d = {} match = zeros(len(variables)) for line in ifile: emptyCells=0 for i in range(len(variables)): regex = r'('+variables[i]+r')[:|=|\(](-… >>> More
OWASP Regex Repository: Is this regex correct?

as seen on Stack Overflow - Search for 'Stack Overflow'
I was looking at the regular expression for validating various data types from the (OWASP Regex Repository). One of the regular expressions in there is called safetext and looks like: ^[a-zA-Z0-9\s.\-]+$ My first question is: Is this regular expression correct? complementary question If this… >>> More
Make a Perl-style regex interpreter behave like a basic or extended regex interpreter

as seen on Stack Overflow - Search for 'Stack Overflow'
I am writing a tool to help students learn regular expressions. I will probably be writing it in Java. The idea is this: the student types in a regular expression and the tool shows which parts of a text will get matched by the regex. Simple enough. But I want to support several different regex… >>> More
JS regex isn't matching, even thought it works with a regex tester

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm writing a piece of client-side javascript code that takes a function and finds the derivative of it, however, the regex that's supposed to match with the power rule fails to work in the context of the javascript program, even though it sucessfully matches when it's used with an independent regex… >>> More
c# RegEx with "|"

as seen on Stack Overflow - Search for 'Stack Overflow'
I need to be able to check for a pattern with | in them. For example an expression like d*|*t should return true for a string like "dtest|test". I'm no regex hero so I just tried a couple of things, like: Regex Pattern = new Regex("s*\|*d"); //unable to build because of single backslash Regex Pattern… >>> More