Question

I need to remove a string A that exists in another string B only if string A is between two spaces.

string A = "e"
string B = "the fifth letter is e "

Example for replacing ‘e’ : "the fifth letter is e " –> "the fifth letter is"

Answer 1

ruby-1.9.2-p290 :006 > a = "the fifth letter is e "
 => "the fifth letter is e " 
ruby-1.9.2-p290 :007 > print a.gsub(/\se\s/,"")
the fifth letter is => nil 

Edited the answer after you edited the question. A possible regular expression to find an “e” character between two space characters is /\se\s/. In this case I’m replacing it with an empty string "". You can use gsub which returns a copy of the string or gsub! to modify the original string.

UPDATE: Since you edited the question again, here’s un updated answer:

ruby-1.9.2-p290 :001 > a = "e"
 => "e" 
ruby-1.9.2-p290 :002 > b = "the fifth letter is e "
 => "the fifth letter is e " 
ruby-1.9.2-p290 :003 > print b.gsub(/\s#{a}\s/,"")
the fifth letter is => nil