From: Xeno Campanoli <xcampanoli@...>
Date: 2008-07-12T14:14:29+09:00
Subject: Re: can ruby replace bash scripts for linux script

Greg Hauptmann wrote:
> hi,
> 
> I need to develop some backup scripts for my linux box. I'm ok with
> Ruby but havn't done bash scripts before.

Bash is a different kind of language, both because it's more devoted to 
handling native unix executables, but also because it's a more primitive 
and older language devoted to doing things in ways they needed to be 
done before the present price/cost of resources.

There are a lot of things you can do much more efficiently in Bash, and 
in far fewer lines.  Also, in Sysadmin land, you may find more of the 
people managing your production boxes will know Bash than Ruby. 
Probably far more.  In my shop, practically everyone is still refusing 
to use Ruby and they want me to write anything I can in Bash, when it's 
at all practical.  To a certain extent I think this kind of request has 
reasonable roots and should be taken into account.

That all being said, and despite the fact that Ruby programs can be 
longer, Ruby programs can be much more readable, IMHO, than Bash 
scripts, especially when the complexity of the program increases beyond 
a few hundred lines of code.  Now I have several Bash scripts that 
include libraries of Bash functions and the entire things are well over 
a thousand lines, and these are still reasonable pieces of software. 
Most things that size make me think of Ruby as the best long term, 
maintainable way to program.  The reasons, again IMHO, include:

	1.  A lot of general facilities which allow for clean solutions
	that would be ugly in Bash.  For instance, I recently ran into a
	Bash script that had sequences of over 10 sed commands to decode
	%nn embedded strings from an HTTP query string.  Ruby has native
	methods for this that you can depend upon.  When you write your
	own, thats gonna be delicate code subject to getting trashed in
	some quick vi edit.

	2.  Class organization, which I like to do when the programmed
	activity is best illustrated with that kind of organization, is
	nicely formalized in Ruby, and requires thought and jury-rigging
	in Bash.

	3.  Loops are very flexible in Ruby.  On the other hand, in Bash
	they may sometimes be more concise.

	4.  Structures in Ruby are generally clearer and more readable:

		if [[ x != 'y' ]]; then
			somefunction $arg1 $arg2
		else
			echo "ERROR:  blek $myevidence"
			exit 1
		fi

		vs Ruby

		if x != 'y' then
			somemethod(arg1,arg2)
		else
			raise Exception, "ERROR:  blek #{myevidence}"
		end

	The difference may not send you, but the extra little tick marks
	 and such can be a big time cost when it comes to debugging and
	maintenance.  Interpolation, as evidenced above, actually uses
	more, but is more clear and flexible, and is always the same.


> 
> Is ruby up to replacing bash shell scripts for this?  (eg calling
> commands, eg rsynch, getting responses etc?

	Yes,  but it's up to you whether you want to spend the time.  I have a 
class I call FlatAccess which has methods like:

	MYUSER=myusername
	SUDOPART = "sudo -u #{MYUSER}"

	def FlatAccess.sudo(shellcmd)
		`#{SUDOPART} #{shellcmd}`
	end

But of course you can just state the command directly like:
result = `sudo -u myusername #{shellcmd}`
---snip---

Now all that being said, there's also something called capistrano that 
does this kind of thing in Ruby for you, so if you're doing that a lot, 
it is worth looking into capistrano.  Perhaps I'll do that myself some 
time soon....

There are a lot of other facilities in native Ruby to do system stuff, 
so the more encompassing answer is:  yes.

One thing I did recently which was interesting was to use pipes and 
threads to collect output from stderr and stdout at the same time from a 
shell execution of curl.

xc

	

> 
> Thanks
> 
>