Ruby - replace the first occurrence of a substring with another string

Question

a = "foobarfoobarhmm"

I want the result to be like "fooBARfoobarhmm"

that is, only the first appearance of "bar" should be replaced by "BAR".

Answer 1

Use #sub :

 a.sub('bar', "BAR") 

Answer 2

String#sub is what you need, as Yossi said. But instead, I would use Regexp, as it is faster:

 a = 'foobarfoobarhmm' output = a.sub(/foo/, 'BAR') 

Answer 3

to replace the first occurrence, simply do the following:

 str = "Hello World" str['Hello'] = 'Goodbye' # the result is 'Goodbye World' 

you can even use regular expressions:

 str = "I have 20 dollars" str[/\d+/] = 500.to_s # will give 'I have 500 dollars'