From: "Peña, Botp" <botp@...>
Date: 2008-08-16T11:46:07+09:00
Subject: Re: [Regex] Alternative for look behind

From: Janus Bor [mailto:janus@urban-youth.com] 
# I need to replace all '-' characters at the beginning of a sequence
# (string) with 'X's (until a character appears that is not '-').
# E.g.
# -------abcde-gh----
# should be changed into
# XXXXXXXabcde-gh----

my initial reaction was not a look behind,

irb(main):062:0> s.gsub(/(^-*)/){$1.tr("-","X")}
=> "XXXXXXXabcde-gh----"


the second was to use oniguruma,

re=Oniguruma::ORegexp.new( '(?<dashes>^-*)(?<after>.*)' )
#=> /(?<dashes>^-*)(?<after>.*)/
s
#=> "-------abcde-gh----"
m=re.match s
#=> #<MatchData:0x2c51b7c>
m[:dashes]
#=> "-------"
m[:after]
#=> "abcde-gh----"
...

nice naming feature, but overkill for this case. ymmv.

kind regards -botp