From: Ara.T.Howard@...
Date: 2004-10-14T01:44:33+09:00
Subject: Re: [nuby] shell-like substitution in a string

On Thu, 14 Oct 2004, Lionel Thiry wrote:

> Hi!
>
> I'd like to make some kind of substitution like in a shell, i.e. having:
> "${tool} -o ${target} -L${libpath} -l${lib} ${source}"
>
> with an env like this:
> env = {
> "tool" => "gcc",
> "target" => "hello.exe",
> "libpath" => "/usr/lib",
> "lib" => "somelib",
> "source" => "hello.c"
> }
>
> it should give:
> "gcc -o hello.exe -L/usr/lib -lsomelib hello.c"
>
>
> It is easy until I want to manage caracter escapement like
> "${var\\}weird}" which should give env["var}weird"],  "\\${var}" which
> should give the simple string "${var}" and "\\\\${var}" which should be
> equivalent to "\\" + env["var"].

i don't think you need to worry about that since 'var}weird' is not a valid
shell identifier - at least i can't seem to create a var by that name in the
shell...

> Any idea of how I could manage that?

you can get bash's exact parameter expansion like this:

   jib:~ > cat a.rb
   require 'session'

   class Expander
     def self::new(*a, &b)
       @instance = super
     end
     def initialize
       @bash = Session::Bash::new
     end
     def expand expr, context = {}
       context.each do |k,v|
         o, e = @bash.execute "#{ k }=#{ v }"
         raise e unless e.empty?
       end
       stdout, stderr = @bash.execute "cat <<eos\n#{ expr }\neos"
       raise stderr unless stderr.empty?
       context.each{|k,v| @bash.execute "unset #{ k }"}
       stdout.chomp
     end
   end

   ex = Expander::new

   expr = "${tool} -o ${target} -L${libpath} -l${lib} ${source}"

   env = {
     "tool" => "gcc",
     "target" => "hello.exe",
     "libpath" => "/usr/lib",
     "lib" => "somelib",
     "source" => "hello.c"
   }

   cmd = ex.expand expr, env
   p cmd


   jib:~ > ruby a.rb
   "gcc -o hello.exe -L/usr/lib -lsomelib hello.c"


-a
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