How do I remove all characters in a string until a substring is matched, in Ruby?

Question

Say I have a string: Hey what\'s up @dude, @how\'s it going?

I\'d like to remove all the characters before@how\'s.

Answer 1

There are literally tens of ways of doing this. Here are the ones I would use:

If you want to preserve the original string:

str = "Hey what's up @dude, @how's it going?"
str2 = str[/@how's.+/mi]
p str, str2
#=> "Hey what's up @dude, @how's it going?"
#=> "@how's it going?"

If you want to mutate the original string:

str = "Hey what's up @dude, @how's it going?"
str[/\A.+?(?=@how's)/mi] = ''
p str
#=> "@how's it going?"

...or...

str = "Hey what's up @dude, @how's it going?"
str.sub! /\A.+?(?=@how's)/mi, ''
p str
#=> "@how's it going?"

You need the \A to anchor at the start of the string, and the m flag to ensure that you are matching across multiple lines.

Perhaps simplest of all for mutating the original:

str = "Hey what's up @dude, @how's it going?"
str.replace str[/@how's.+/mi]
p str
#=> "@how's it going?"