Bug #18271: Regexp inconsistency (repeatable)

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux]
• Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN

[hanHoll (Han Holl)]

han:~/au> irb >> st = 'A. C. Cobble'
=> "A. C. Cobble"

st.gsub(/. ([A-Z])(?=.)/, ".#{$1}")
=> "A.. Cobble"
st.gsub(/. ([A-Z])(?=.)/, ".#{$1}")
=> "A.C. Cobble"
RUBY_VERSION
=> "3.0.2"

[zverok (Victor Shepelev)]

$1 is global variable, "#{$1}" is evaluated BEFORE the method call, making a string "whatever was in $1 at that moment":

st = 'A. C. Cobble'

'foobar' =~ /f(.{2})/ # unrelated regex call, sets $1 to "oo"

st.gsub(/. ([A-Z])(?=.)/, ".#{$1}") # it is now an equivalent to calling with second arg = ".oo"
# => "A.oo.ooobble"

If I am understanding correctly what you want to achieve, you need to use \1 (meaning "first group of currently evaluating regexp"):

st.gsub(/. ([A-Z])(?=.)/, '.\1')
# => "A.C.Cobble"

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed