Ruby (or Python) Instead of Shell

Question

Since I am conversant in Ruby, I am about to script a few things on OSX using it. But then I thought, perhaps I am missing the boat. I know a lot of reasons to prefer Ruby over Bash (or whatever sh-compatible command language interpreter), but I don't know any reasons not to. What is the upside of programming the shell directly?

I intend to take advantage of system commands using system whenever necessary.

Note: I already know that Ruby won't always be there, but I'm interested in mostly technical, semantic and syntactic criteria.

Edit: By Ruby not always being there, I mean that it is not a standard part of all *nix distributions, unlike vi.

Answer 1

The shell's programming language is awful for all but one thing.

Pipelines.

The shell's programming language for pipelines totally rocks.

The |, & and ; operators, plus () and ``` form a tidy little language for describing pipelines.

a & b is concurrent

a ; b is sequential

a | b is a pipeline where a feeds b

That part of shell programming rocks.

Think of ( a & b & c ) | tee capture | analysis as the kind of thing that's hard to express in Python (or Ruby). You can do much of this with iterpipes, but not quite all of it.

Much of the rest you can live without, and use Python (or Ruby) and you'll be happier and more productive.

The biggest thing to watch out for is anything involving expr at the shell level. As soon as you start trying to do "calculations", you've crossed out of the shell's sweet spot and you should stop programming in the shell and rethink what you're doing.

Answer 2

The core functionality in bash is to run other command line applications. Making those programs interact with each other etc. This is not what ruby is designed for (right?).

Answer 3

Shell's programming languages have a very small footprint and very few dependencies. Beside that I can't see much point using it. Personnaly I prefer using Perl or python for such tasks.

Answer 4

I don't see any problem with Ruby. You can use the back-tick instead of system and insert things inline like

`cp ${source} ${dest}` 

Also, you can easily get the contents of stdout (not sure about stdin) and form your own little pipelining thing.

I think Ruby is a win for doing scripting stuff, but less so as a general shell because of the clunky bit of always having to remember to put back-ticks to execute commands.

Answer 5

Directly writing Posix or bash script works out well for operations that loop over lists of files. Things like

find . -name \*.htm | while read x; do
   # whatever
done

The shell can do command substitution and simple parameter transformations reasonably well. Shell procedures allow fairly complex programs to be reasonably modular.

The transition to something like Ruby happens when some kind of internal data structure is needed. The shell is a macro processor, so it is capable of something like "metaprogramming" where you make up variables names. Some versions of bash have arrays and all versions can "metaprogram" variable names where the index is part of the name.

But it's 100% hack and even the built-in arrays are crude. Once decisions have to be made and data structures retained, it's time to switch to Ruby.

Answer 6

The comments about how the shell handles piping are spot on. However, if you are interested in a rubyish approach to the shell you might look at rush. There are immediate observations (outside of how piping is handled) such as paths are now handled in an entirely different way, but if what you want is the ease of ruby things like iterators and blocks you have that at your fingertips.

Likely not a full replacement in any case, but it might serve your purpose.

[Edit] A quick look around turned up ipython which looks (at a cursory glance) to give more of the natural feel of a shell environment which may or may not be an incentive for you.

Answer 7

Ruby has a massive advantage: you know Ruby and (I assume) you don't know Bash that well!

Personally I use Ruby for complex scripts and Bash for simple ones -- the breakpoint for me is usually anything that actually has a proper set of command line parameters -- but then, I know both Bash and Ruby.

I would advise you to use Bash for anything that is simple enough that you can work it out on the commandline beforehand, for example:

who |grep -i admin |cut -c10-20 

-- and use Ruby for anything else

Answer 8

@OP, if you want to compare Ruby vs Shell, compare using Ruby's interpreter( without libraries/modules). ie compare its in-builts against the shell. Otherwise, they are almost the same. Why? For example, if you want to do advanced maths other than those provided by the shell, the shell can use bc/awk/dc. Those are the math "libraries" for the shell. If you want date structures such as associative arrays, you can use awk. (equivalent to hashes in ruby). In modern bash shell, there are also associative arrays. You can think of *nix external tools (eg wc,grep,sed etc and those in /usr/bin/, /usr/sbin etc) as the shell's "libraries".

Lastly, if you intend to use system() a lot in Ruby, i suggest using the shell as one of them mentioned, the shell excels in pipes. etc..