From: Robert Klemme <bob.news@...>
Date: 2003-10-06T17:40:32+09:00
Subject: Re: backquotes, system, shell and ruby


"John Carter" <john.carter@tait.co.nz> schrieb im Newsbeitrag
news:Pine.LNX.4.58.0310031253560.10643@parore.tait.co.nz...
> Somebody suggested I use zsh instead of bash for my commandline, so I
> looked at it, looked at the syntax for tweaking the profile files, and
> said...
> "Yuck! Another badly designed syntax! Why can't I just use Ruby?"
>
> And that got me thinking.
>
> Consider backquotes.
>
> a = `wc *.c`
>
> What did that do? Same as open("|wc *.c").
>
> It ran bash!
>
> Yuck!
>
> system( "tar -xvzf foo.tgz foo")
>
> What did that do? It ran shell!
>
> Why? Why does a scripting language like Ruby keep invoking an old and
bad
> scripting language call shell?
>
> Because...

.... you did not invoke it with an array.

>  a) Ruby doesn't have a good syntax for invoking and dealing with
>     processes and pipes between processes.
>
>  b) Ruby doesn't have a built in understanding of ENV['PATH']
>
>  c) Ruby doesn't have such a simple syntax for globbing (beyond
>     Dir['*.c'])

???

ruby -e 'p Dir["/cygdrive/c/temp/ruby/*.{rb,bak}"]'
ruby -e 'p Dir["/cygdrive/c/temp/**.{rb,bak}"]'

That's quite powerful and simple.

>     Consider the "rename" facility that comes with perl these days.
>        For example, to rename all files matching "*.bak" to strip the
exten-
>        sion, you might say
>
>                rename 's/\.bak$//' *.bak

ruby -e 'Dir["*.bak"].each {|f| File.rename(f, f.gsub(/\.bak$/, ""))}'

>        To translate uppercase names to lower, you'd use
>
>                rename 'y/A-Z/a-z/' *

ruby -e 'Dir["*"].each {|f| File.rename(f, f.upcase)}'
ruby -e 'Dir["*"].each {|f| File.rename(f, f.tr("a-z", "A-Z"))}'

>    Ooh! Looky! Nice! Wouldn't it be nice to have the power of ruby
>    intertwingled with the commandline.
>
>
> Ruby does have Shell.rb, which takes us halfway there. (If it had
> decent docs...)
>
> How hard would it be to extend the backtick syntax to be a pure ruby
> thing. ie. So proc_exec doesn't invoke bash, but invokes Shell.rb?
>
>
> Hmm. Could we even do this entirely in UserLand? ie. Couldn't we
> override proc_exec and replace it with ruby code that parses the
> string, handles the redirects, variable interpolation quoting and
> forks, then just directly execs the program without ever touching sh?

We could - but I wouldn't make this the default since every shell has it's
own pecularities (i.e. different syntax and built in commands.  Why not
simply write a method that takes a string and returns an array processed
according to a particular shell convention?  Then you can do

system( bashParse( "ls -lf *.bak" ) )

which is quite simple IMHO.

But I would leave in the default shell invocation because that gives most
flexibility.

Regards

    robert