re = /(?: # Non capturing group 1
\G # Matches where the regex engine stops in the previous step
(\w+) # capture group 1: a regex word of 1+ chars
\h* # zero or more horizontal spaces (space, tabs)
(?: # Non capturing group 2
=\h* # literal '=' follower by zero or more hspaces
(\w+) # capture group 2: a regex word of 1+ chars
)? # make the non capturing group 2 optional
)+ # repeat the non capturing group 1, one or more/x
str = 'Key name = value'
subst = '\\1\\2'
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html