sub_and_gsub_in_ruby.md

.sub and .gsub in ruby

Both methods are for replacing part of a string.

.sub

String#sub method allows to replace first occurrence of pattern to another substring.

"some string with spaces".sub(" ", "_") # => "some_string with spaces"

.gsub

String#gsub method allows to replace all occurrences of pattern to another substring.

"some string with spaces".sub(" ", "_") # => "some_string_with_spaces"

Additional info

Both .sub and .gsub methods create a new string. So if you have a variable

my_string = "my string with spaces"
my_string.sub("my string", "new string") # => "new string with spaces"
my_string # => "my string with spaces"

If you want to transform string in place, you can add ! character to those methods (resulting in .sub! & .gsub!)

my_string = "my string with spaces"
my_string.sub!("my string", "new string") # => "new string with spaces"
my_string # => "new string with spaces"