String literal without need to escape backslash - ruby

In C#, I can write backslashes and other special characters without escaping by using # before a string, but I have to escape double-quotes.
C#
string foo = "The integer division operator in VisualBASIC is written \"a \\ b\"";
string bar = #"The integer division operator in VisualBASIC is written \"a \ b\""
In Ruby, I could use the single-quote string literal, but I'd like to use this in conjuction with string interpolation like "text #{value}". Is there an equivalent in Ruby to # in C#?

There is somewhat similar thing available in Ruby. E.g.
foo = %Q(The integer division operator in VisualBASIC is written "a \\ b" and #{'interpolation' + ' works'})
You can also interpolate strings in it. The only caveat is, you would still need to escape \ character.
HTH

You can use heredoc with single quotes.
foo = <<'_'
The integer division operator in VisualBASIC is written "a \ b";
_
If you want to get rid of the newline character at the end, then chomp it.
Note that this does not work with string interpolation. If you want to insert evaluated expressions within the string, you can use % operation after you create the string.
foo = <<'_'
text %{value}
_
foo.chomp % {value: "foo"}

Related

Why ruby controller would escape the parameters itself?

I am writing Ruby application for the back end service. There is a controller which would accept request from front-end.
Here is the case, there is a GET request with a parameter containing character "\n".
def register
begin
request = {
id: params[:key]
}
.........
end
end
The "key" parameter is passing from AngularJs as "----BEGIN----- \n abcd \n ----END---- \n", but in the Ruby controller the parameter became "----BEGIN----- \\n abcd \\n ----END---- \\n" actually.
Anyone has a good solution for this?
Yes, this is because of the ruby way to read the escape character. You can read the explanation right here: Escaping characters in Ruby
I got this issue once, and I just use gsub! to change the \\n to \n. What you should do is:
def register
begin
request = {
id: params[:key].gsub!("\\n", "\n")
}
.........
end
end
Remember, you have to use double quotation " instead of single quotation '. From the link I gave:
The difference between single and double quoted strings in Ruby is the way the string definitions represent escape sequences.
In double quoted strings, you can write escape sequences and Ruby will output their translated meaning. A \n becomes a newline.
In single quoted strings however, escape sequences are escaped and return their literal definition. A \n remains a \n.

How can I get a non-interpolation bash escape in Ruby?

In ruby, the backticks are a system call, but they are interpolation. This is nice as I could do this
a = 20.sqrt
`cat #{a}`
But it is also annoying because I sometimes want \ in my code, but I need \\ within `` because it is interpolation and escaping. How can I avoid this?
Try this
Kernel.`('echo "#{a}"')
Which prints verbatim
#{a}
Fun fact, ` is actually a method on Kernel and you can call it just like any other method. And thus pass a single quote string as argument.
Form the string in a nonescaping context and interpolate it into the backticks:
s = %{echo "he\ny"}
puts `#{s}`
If you need to juggle with escape characters, you could instead use %q :
system(%q{echo '#&%$][/\'})
#=> #&%$][/\
If you want string interpolation, you can use %Q :
a = 20
system(%Q{echo '#{a}&%$][/\'})
#=> 20&%$][/
Here's a thread about it. Note that you can use any delimiter after %q and %Q : pick one that isn't in your string!
I used system here instead of %x{} or ticks. They're not equivalent, but I just wanted to show the string definition without making the line even more complex than it already is.

unterminated string meets end of file

Following is my code:
md5 = Digest::MD5.new
md5 << "!##$"
Then comes the error:
SyntaxError: (irb):46: unterminated string meets end of file
What is wrong? And how can I calculate the md5 hash of the string "!##$"?
The hash # sign in double quoted strings is used for variable and expression substitution. In this case, you are substituting the value of the global variable $" into the string, but you are not closing the string. The syntactically correct way of expressing that would be
"!##$"" # Note the extra closing quotes
However, it seems that you actually don't want to do variable substitution anyway, in which case you should always use single quoted strings:
'!##$'
Seems like you need to quote #:
> puts "!#\#$"
!##$
Your problem is the string you got is in a double apostrophe (") - so it is interpreted. And you have a hash (#) inside, so it is trying to do expression substitution. Put the string in a single apostrophe:
md5 << '!##$'

Ruby string sub without regex back references

I'm trying to do a simple string sub in Ruby.
The second argument to sub() is a long piece of minified JavaScript which has regular expressions contained in it. Back references in the regex in this string seem to be effecting the result of sub, because the replaced string (i.e., the first argument) is appearing in the output string.
Example:
input = "string <!--tooreplace--> is here"
output = input.sub("<!--tooreplace-->", "\&")
I want the output to be:
"string \& is here"
Not:
"string & is here"
or if escaping the regex
"string <!--tooreplace--> is here"
Basically, I want some way of doing a string sub that has no regex consequences at all - just a simple string replace.
To avoid having to figure out how to escape the replacement string, use Regex.escape. It's handy when replacements are complicated, or dealing with it is an unnecessary pain. A little helper on String is nice too.
input.sub("<!--toreplace-->", Regexp.escape('\&'))
You can also use block notation to make it simpler (as opposed to Regexp.escape):
=> puts input.sub("<!--tooreplace-->") {'\&'}
string \& is here
Use single quotes and escape the backslash:
output = input.sub("<!--tooreplace-->", '\\\&') #=> "string \\& is here"
Well, since '\\&' (that is, \ followed by &) is being interpreted as a special regex statement, it stands to reason that you need to escape the backslash. In fact, this works:
>> puts 'abc'.sub 'b', '\\\\&'
a\&c
Note that \\\\& represents the literal string \\&.

Escaping single and double quotes in a string in ruby?

How can I escape single and double quotes in a string?
I want to escape single and double quotes together. I know how to pass them separately but don't know how to pass both of them.
e.g: str = "ruby 'on rails" " = ruby 'on rails"
My preferred way is to not worry about escaping and instead use %q, which behaves like a single-quote string (no interpolation or character escaping), or %Q for double quoted string behavior:
str = %q[ruby 'on rails" ] # like single-quoting
str2 = %Q[quoting with #{str}] # like double-quoting: will insert variable
See https://docs.ruby-lang.org/en/trunk/syntax/literals_rdoc.html#label-Strings and search for % strings.
Use backslash to escape characters
str = "ruby \'on rails\" "
Here is a complete list:
From http://learnrubythehardway.org/book/ex10.html
You can use Q strings which allow you to use any delimiter you like:
str = %Q|ruby 'on rails" " = ruby 'on rails|
>> str = "ruby 'on rails\" \" = ruby 'on rails"
=> "ruby 'on rails" " = ruby 'on rails"
I would go with a heredoc if I'm starting to have to worry about escaping. It will take care of it for you:
string = <<MARKER
I don't have to "worry" about escaping!!'"!!
MARKER
MARKER delineates the start/end of the string. start string on the next line after opening the heredoc, then end the string by using the delineator again on it's own line.
This does all the escaping needed and converts to a double quoted string:
string
=> "I don't have to \"worry\" about escaping!!'\"!!\n"
I would use just:
str = %(ruby 'on rails ")
Because just % stands for double quotes(or %Q) and allows interpolation of variables on the string.
Here is an example of how to use %Q[] in a more complex scenario:
%Q[
<meta property="og:title" content="#{#title}" />
<meta property="og:description" content="#{#fullname}'s profile. #{#fullname}'s location, ranking, outcomes, and more." />
].html_safe
One caveat:
Using %Q[] and %q[] for string comparisons is not intuitively safe.
For example, if you load something meant to signify something empty, like "" or '', you need to use the actual escape sequences. For example, let's say qvar equals "" instead of any empty string.
This will evaluate to false
if qvar == "%Q[]"
As will this,
if qvar == %Q[]
While this will evaluate to true
if qvar == "\"\""
I ran into this issue when sending command-line vars from a different stack to my ruby script. Only Gabriel Augusto's answer worked for me.

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