Contents
Outline
In this blog post, I will introduce how to use the String in Ruby.
Search
In Ruby, you can search the string by the index method.
puts "ABCD".index("C")
# 2
If the searched string is in the string, the index method returns the index of the string position. If the searched string doesn’t exist, nil is returned.
Replace
we can refer to the string via index, and replace the string via index.
a = "Apple Juice"
a[0] = "O"
a[1] = "r"
a[2] = "a"
a[3] = "n"
a[4] = "ge"
puts a
# Orange Juice
As you see above, we can replace between the different the length of the strings like a[4] = "ge".
Regular expression
Like other languages, you can use the regular expression to search the string in Ruby.
Meta characters
In the regular expression, we use the meta characters to make the regular expression.
| Meta characters | Description |
|---|---|
| [] | single character in [] |
| . | any one character |
| * | repeat the last expression more than zero times. |
| + | repeat the last expression more than once. |
| ? | repeat the last expression more than zero times or once. |
| () | regular expression group |
| a|b | one character in a, b |
| \s | space character |
| \w | alphanumeric or underbar(_) |
| \d | number(0~9) |
| ^ | the front of the string |
| $ | the end of the string |
Pattern matching
You can search the string by the regular expression.
puts /R.by/ =~ "Let's study Ruby!"
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Like the index method, if the pattern is matched, the index of the string is returned. if the pattern is not matched, nil is returned.
Regexp class
You can make the regular expression object by the new method of the Regexp like below.
re = Regexp.new("R.by")
puts re =~ "Let's study Ruby!"
# 12
Regular expression objects
You can use more efficiently the regular expression with the regular expression objects.
Regular expression object
x: If you usex, you can add the comments in the regular expression.re =/R.by # Search Ruby/x puts re =~ "Let's study Ruby!" # 12Regular expression object
i: If you usei, you can search the string without case-sensitive.re =/r.by/i puts re =~ "Let's study Ruby!" # 12
Symbol
The Symbol is a class that identifies the variable. It is like the memory address of the variables.
a = :apple
b = :apple
c = :orange
puts a == b # true
puts a == c # false
In the above, a and b is the same symbol, so it means the same objects.
Symbol and String
You can convert the Symbol to the String by to_s, and the String to the Symbol by intern.
a = :apple
b = "apple"
puts a # apple
puts b # apple
puts a == b # false
puts a.to_s == b # true
puts a == b.intern # true
Usages of the Symbol
The Symbol is like the memory address, so it’s faster and better for the memory that using the String.
def triangle(value)
value[:a] + value[:b] + value[:c]
end
test = {:a => 5, :b => 2, :c => 5}
puts triangle(test)
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The Symbol is normally used for the Hash keys.
Percent technique
Normally, the String is in the double quotation(“) or single quotation(‘), but we can use % for it.
puts %{This string has " character}
# This string has " character
puts %Q{This string has " character}
# This string has " character
puts %q{This string has ' character}
# This string has ' character
Also, we can convert the string includes the space divisions to the array by %w.
puts %w(apple orange banana)
# apple
# orange
# banana
Completed
We’ve seen how to use the string in Ruby. The regular expression is used in other languages, so if you remember it, you can use it in many places.
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