From: Jim Menard <jimm@...>
Date: 2000-11-02T22:40:01+09:00
Subject: [ruby-talk:5988] Putting backslash before \1

I am trying to create a string by preceeding all backslashes or tabs in the
original with a backslash. For example,

     makeSafe("a\tb")    => "a\\\tb"
     makeSafe("a\\b")    => "a\\\\b"

I can't figure out how to use gsub() to do this. Specifically,  I can't
figure out how to preceed '\1' with a backslash. For example (output
below):

    str = "tab:\tand backslash:\\done"
    puts str.gsub(/([\\\t])/, '\1')   # Should do nothing.
    puts str.gsub(/([\\\t])/, '\\1')  # Should do nothing ('\\1' same as
    '\1').
    puts str.gsub(/([\\\t])/, '\\\1') # Help! Want backslashes before \1.
    puts str.gsub(/([\\\t])/, '\\' + '\1') # How about this? No good.

Output:

    tab:    and backslash:\done    ("tab:\tand backslash:\\done")
    tab:    and backslash:\done    ("tab:\tand backslash:\\done")
    tab:\1and backslash:\1done    ("tab:\tand backslash:\\done")
    tab:\1and backslash:\1done    ("tab:\\1and backslash:\\1done")

(My workaround? Two separate substitutions that "know" what character they
are looking  for:)

    def makeSqlSafe(str)
    copy = str
    copy.gsub!(/\t/, "\\\t")
    copy.gsub!(/\\/, "\\\\")
    return copy
    end

Any suggestions or better workarounds? Is this a Ruby bug, or am I
misunderstanding the use of '\1' and '\\1'? Thanks for your time and help.

Jim
-- 
Jim Menard   jimm@io.com   http://www.io.com/~jimm/   BeOS developer #1283
"The reason why there is no good commercial Java develoment environment
is that the only folks that are good enough to write one all use EMACS."
    -- Unknown, on comp.lang.java.programmer