String has several methods that can be used to manipulate strings.
These methods are called on the string itself and are often chained together to perform multiple operations on a string.
The following is a list of some of the most common methods.
See the String API documentation for a complete list of methods.
String#upcase & String#downcase
The upcase method returns a new string with all the characters converted to uppercase.
"hello".upcase
# => "HELLO"
The downcase method returns a new string with all the characters converted to lowercase.
"HELLO".downcase
# => "hello"
String#sub & String#gsub
Crystal has methods for replacing parts of a string.
These are known as sub (substitution) and gsub (global substitution).
These methods can take a string, char, or regex as the first argument and a string or char as the second argument.
The first argument is the part of the string that will be replaced, and the second argument is the replacement.
Char and regex will be explained in later concepts.
The sub method will replace the first occurrence of the first argument with the second argument.
"hello".sub("l", "r")
# => "herlo"
The gsub method works the same as sub but will replace all occurrences of the first argument with the second argument.
"hello".gsub("l", "r")
# => "herro"
String#chomp & String#strip
Chomp and strip can be used to remove unwanted characters from a string.
The chomp method will be default remove the last \r, \n or \r\n characters from a string.
If the method is called with an argument, it will remove the given value from the end of the string.
If it does exist at the end of the string.
"hello\n".chomp
# => "hello"
"hello".chomp("llo")
# => "he"
By default, the strip method will remove all whitespace from the beginning and end of a string.
If the method is called with an argument, it will remove that argument from the beginning and end of the string.
If it does exist at the beginning or end of the string.
" hello ".strip
# => "hello"
String#index
The index method can be used to find a character's index in a string.
The index method takes a String, Char, or regex as an argument.
It can take an optional second argument to specify the index from which to search.
The index method will return the index of the first occurrence of the argument.
"hello".index("l")
# => 2
"hello".index("l", 3)
# => 3
String#delete_at
You can use the delete_at method to remove a character from a string.
The delete_at method takes an index as an argument and will remove the character at that index.
"hello".delete_at(0)
# => "ello"
"hello".delete_at(3)
# => "helo"
String#insert
The insert method can be used to insert a string at a specific index.
The insert method takes an index as the first argument and a string as the second argument.
The insert method will return a new string with the second argument inserted at the index.
"hello".insert(0, "h")
# => "hhello"
"hello".insert(3, "l")
# => "helllo"
Learning Exercise
