I want to insert backslash before apostrophe in "children's world" string. Is there a easy way to do it?
irb(main):035:0> s = "children's world"
=> "children's world"
irb(main):036:0> s.gsub('\'', '\\\'')
=> "childrens worlds world"
Answer
You need some extra backslashes:
>> puts "children's world".gsub("'", '\\\\\'')
children\'s world
or slightly more concisely (since you don't need to escape the ' in a double-quoted string):
>> puts "children's world".gsub("'", "\\\\'")
children\'s world
or even more concisely:
>> puts "children's world".gsub("'") { "\\'" }
children\'s world
Explanation
Your '\\\'' generates \' as a string:
>> puts '\\\''
\'
and \' is a special replacement pattern in Ruby. From ruby-doc.org:
you may refer to some special match variables using these combinations ... \' corresponds to $', which contains string after match
So the \' that gsub sees in the second argument is being interpreted as a special pattern (everything in the original string after the match) instead of as a literal \'.
So what you want gsub to see is actually \\', which can be produced by '\\\\\'' or "\\\\'".
Or, if you use the block form of gsub (gsub("xxx") { "yyy" }) then Ruby takes the replacement string "yyy" literally without trying to apply replacement patterns.
Note: If you have to create a replacement string with a lot of \s you could take advantage of the fact that when you use /.../ (or %r{...}) you don't have to double-escape the backslashes:
>> puts "children's world".gsub("'", /\\'/.source)
children\'s world
Or you could use a single-quoted heredoc: (using <<'STR' instead of just <<STR)
>> puts "children's world".gsub("'", <<'STR'.strip)
\\'
STR
children\'s world
>> puts s.gsub("'", "\\\\'")
children\'s world
Your problem is that the string "\'" is meaningful to gsub in a replacement string. In order to make it work the way you want, you have to use the block form.
s.gsub("'") {"\\'"}
Related
How can I format "hello bro" to obtain "hello\ bro" in ruby.
When I use "...".gsub /\s/,'\\ ', I obtain "hello\\ bro" which bash cannot read. The '\ ' replacement has no effect.
Thanks
Your gsub arguments are actually correct. If you're running it through irb, it may not be obvious though - backslashes are escaped in the console output. For instance:
irb(main):036:0> my_str = "hello bro".gsub /\s/, '\\ '
=> "hello\\ bro"
However, we'll see the expected string when we output the value of my_str:
irb(main):043:0> puts my_str
hello\ bro
That said, unless you're absolutely sure that spaces are the only characters you need to escape, you're better off using something like Shellwords, as mentioned in the comments.
So I'm having an issue replacing \" in a string.
My Objective:
Given a string, if there's an escaped quote in the string, replace it with just a quote
So for example:
"hello\"74" would be "hello"74"
simp"\"sons would be simp"sons
jump98" would be jump98"
I'm currently trying this: but obviously that doesn't work and messes everything up, any assistance would be awesome
str.replace "\\"", "\""
I guess you are being mistaken by how \ works. You can never define a string as
a = "hello"74"
Also escape character is used only while defining the variable its not part of the value. Eg:
a = "hello\"74"
# => "hello\"74"
puts a
# hello"74
However in-case my above assumption is incorrect following example should help you:
a = 'hello\"74'
# => "hello\\\"74"
puts a
# hello\"74
a.gsub!("\\","")
# => "hello\"74"
puts a
# hello"74
EDIT
The above gsub will replace all instances of \ however OP needs only to replace '" with ". Following should do the trick:
a.gsub!("\\\"","\"")
# => "hello\"74"
puts a
# hello"74
You can use gsub:
word = 'simp"\"sons';
print word.gsub(/\\"/, '"');
//=> simp""sons
I'm currently trying str.replace "\\"", "\"" but obviously that doesn't work and messes everything up, any assistance would be awesome
str.replace "\\"", "\"" doesn't work for two reasons:
It's the wrong method. String#replace replaces the entire string, you are looking for String#gsub.
"\\"" is incorrect: " starts the string, \\ is a backslash (correctly escaped) and " ends the string. The last " starts a new string.
You have to either escape the double quote:
puts "\\\"" #=> \"
Or use single quotes:
puts '\\"' #=> \"
Example:
content = <<-EOF
"hello\"74"
simp"\"sons
jump98"
EOF
puts content.gsub('\\"', '"')
Output:
"hello"74"
simp""sons
jump98"
How can i say "all symbols except backslash" in Ruby character class?
/'[^\]*'/.match("'some string \ hello'") => should be nil
Variant with two backslashed doesn't work
/'[^\\]*'/.match("'some string \ hello'") => 'some string \ hello' BUT should be nil
Your problem is not with your regex; you got that right. Your problem is that your test string does not have a backslash in it. It has an escaped space, instead. Try this:
str = "'some string \\ hello'"
puts str #=> 'some string \ hello'
p /'[^\\]*'/.match(str) #=> nil
You need to escape the backslash:
[^\\]*
because backslash is the escape character in regular expressions, thus escaping the closing bracket here.
If you want to verify that the whole string contains non-backslash characters, then you need anchors:
^[^\\]*$
There's actually not a backslash in your string to match against. Try taking a look at just your input:
"'some string \ hello'".length # => 20
"a\ b".length # => 3
The "\ " in double quotes is being escaped into just a space:
irb(main):014:0> " "[0].to_i # => 32
irb(main):015:0> "\ "[0].to_i # => 32
irb(main):016:0> "\ ".size #=> 1
If you want to match no slash, you'll need two, like in your second example, which looks good to me:
/'[^\\]*'/.match("'some string \\ hello'") # => nil
This is relevant to Csharp.. but idk it might help you.
[^\\\\]*
four slashes instead of two.
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?
Escaping is limited when using single quotes rather then double quotes:
puts 'sinlge\nquote'
puts "double\nquote"
"\0" is the null-character (used i.e. in C to determine the end of a string), where as '\0' is "\\0", therefore both 'hello'.gsub(/.+/, '\0') and 'hello'.gsub(/.+/, "\\0") return "hello", but 'hello'.gsub(/.+/, "\0") returns "\000". Now 'hello'.gsub(/.+/, '\\0') returning 'hello' is ruby trying to deal with programmers not keeping the difference between single and double quotes in mind. In fact, this has nothing to do with gsub: '\0' == "\\0" and '\\0' == "\\0". Following this logic, whatever you might think of it, this is how ruby sees the other strings: both '\\\0' and '\\\\0' equal "\\\\0", which (when printed) gives you \\0. As gsub uses \x for inserting match number x, you need a way to escape \x, which is \\x, or in its string representation: "\\\\x".
Therefore the line
puts 'hello'.gsub(/.+/, "\\0 \\\\0 \\\\\\0 \\\\\\\\0")
indeed results in
hello \0 \hello \\0
I don't understand what is going on here. How should I feed gsub to get the string "Yaho\'o"?
>> "Yaho'o".gsub("Y", "\\Y")
=> "\\Yaho'o"
>> "Yaho'o".gsub("'", "\\'")
=> "Yahooo"
\' means $' which is everything after the match.
Escape the \ again and it works
"Yaho'o".gsub("'", "\\\\'")
"Yaho'o".gsub("'", "\\\\'")
Because you're escaping the escape character as well as escaping the single quote.
This will also do it, and it's a bit more readable:
def escape_single_quotes(str)
str.gsub(/'/) { |x| "\\#{x}" }
end
If you want to escape both a single-quote and a backslash, so that you can embed that string in a double-quoted ruby string, then the following will do that for you:
def escape_single_quotes_and_backslash(str)
str.gsub(/\\|'/) { |x| "\\#{x}" }
end