Ruby String Prepend '\' Character

Appending to an existing string

You can use << to append to a string in-place.

s = "foo"
old_id = s.object_id
s << "bar"
s                      #=> "foobar"
s.object_id == old_id  #=> true

How to add string \n literally at the end of each line in Ruby?

String#gsub/String#gsub! plus a very simple regular expression can be used to achieve that:

str = "line1
       line2
       line3"
str.gsub!(/$/, ' \n')
puts str

Output:

line1 \n
       line2 \n
       line3 \n

How do I add characters between each character in a string in ruby?

There are many solutions to this, I would suggest the following :

1/ split the string into an array of individual characters with chars

"hello".chars
=> ["h", "e", "l", "l", "o"]

2/ join them with the two characters you want to add in-between each character

["h", "e", "l", "l", "o"].join('--')
=> "h--e--l--l--o"

You can execute this in one line as such :

"hello".chars.join('--')

How to delete specific characters from a string in Ruby?

Do as below using String#tr :

 "((String1))".tr('()', '')
 # => "String1"

How to mask all but last four characters in a string

positive lookahead

A positive lookahead makes it pretty easy. If any character is followed by at least 4 characters, it gets replaced :

"654321".gsub(/.(?=.{4})/,'#')
# "##4321"

Here's a description of the regex :

r = /
     .        # Just one character
     (?=      # which must be followed by
        .{4}  # 4 characters
     )        #
    /x        # free-spacing mode, allows comments inside regex

Note that the regex only matches one character at a time, even though it needs to check up to 5 characters for each match :

"654321".scan(r)
# => ["6", "5"]

/(.)..../ wouldn't work, because it would consume 5 characters for each iteration :

"654321".scan(/(.)..../)
# => [["6"]]
"abcdefghij".scan(/(.)..../)
# => [["a"], ["f"]]

If you want to parametrize the length of the unmasked string, you can use variable interpolation :

all_but = 4
/.(?=.{#{all_but}})/
# => /.(?=.{4})/

Code

Packing it into a method, it becomes :

def mask(string, all_but = 4, char = '#')
  string.gsub(/.(?=.{#{all_but}})/, char)
end

p mask('testabcdef')
# '######cdef'
p mask('1234')
# '1234'
p mask('123')
# '123'
p mask('x')
# 'x'

You could also adapt it for sentences :

def mask(string, all_but = 4, char = '#')
  string.gsub(/\w(?=\w{#{all_but}})/, char)
end

p mask('It even works for multiple words')
# "It even #orks for ####iple #ords"

Some notes about your code

string.to_s

Naming things is very important in programming, especially in dynamic languages.

string.to_s

If string is indeed a string, there shouldn't be any reason to call to_s.

If string isn't a string, you should indeed call to_s before gsub but should also rename string to a better description :

object.to_s
array.to_s
whatever.to_s

join

puts array.join(", ").delete(", ").inspect

What do you want to do exactly? You could probably just use join :

[1,2,[3,4]].join(", ").delete(", ")
# "1234"
[1,2,[3,4]].join
# "1234"

delete

Note that .delete(", ") deletes every comma and every whitespace, in any order. It doesn't only delete ", " substrings :

",a b,,,   cc".delete(', ')
# "abcc"
["1,2", "3,4"].join(', ').delete(', ')
# "1234"

How to check whether a string contains a substring in Ruby

You can use the include? method:

my_string = "abcdefg"
if my_string.include? "cde"
   puts "String includes 'cde'"
end

Inserting Escape Characters

I assume you are reffering to the following problem:

"\\n".gsub(/\\\\/, "\\").gsub(/\\n/, "\n") # => "n"
"\\n".gsub(/\\n/, "\n").gsub(/\\\\/, "\\") # => "\\\n"

String#gsub can take a block argument, which performs the substitution.

str.gsub(/\\(.)/) do |s|
  case $1
  when "n"
    "\n"
  when "t"
    "\t"
  else
    $1
  end
end

This way no special escape sequence is substituted first and everything works as expeted.

---

Related Topics