From: Steve Pauly <stevepauly@...>
Date: 2010-07-02T11:09:32+09:00
Subject: Re: Running a shell command from ruby

Josh Cheek wrote:
> On Thu, Jul 1, 2010 at 7:02 PM, Josh Cheek <josh.cheek@gmail.com> wrote:
> 
>>> #!/usr/bin/ruby
>>>
>> It has to do with block bindings. do ... end bind to the furthest left
>> script1=["touch ~/ruby/f1;touch ~/ruby/f2"]    #addl array elements to be
>> added
>> puts script1[0].split(/;/) do |k|
>>  puts k
>>  system(k)
>> end
>>
>>
>>
> 
> Here is a solution that creates the files.
> 
> ----------
> 
> script1=["touch ~/f1;touch ~/f2"]    #addl array elements to be added
> script1[0].split(/;/).each do |k|
>  puts k
>  system k
> end
> 
> ----------
> 
> Note that {} has the kind of binding that you were looking for, but that
> split does not take a block (which is why I added the each method).
> 
> though I don't understand your format, are you wanting them to be 
> separated
> by being elements in an array, or by splitting a string on semicolons? 

My idea, as a learning exercise only,was to prove to myself that I could 
use an array of strings to contain "multiple" bash commands in "each" 
array element. Of course, my use of a ";" to delimit is probably ill 
advised, but was done merely for a proof of concept.

Now that with the addition of ".each", it works and mystery (for me) 
solved.

I will have to study your code below more.

Thanks to all.
Steve.




> Right
> now, any other elements in this array will be ignored, because you only 
> look
> at the one in index zero. (what is the point of the Array?)
> 
> But you also have an issue if you split on semicolons, that assumes all
> semicolons are valid delimiters.  Depending on context, this may not be 
> the
> case. For example, what if the String was:
> %{echo "if ARGV.empty? ; puts 'no args' else puts 'got args' end" >
> argchecker.rb ; ruby argchecker.rb 1 2 3 ; ruby argchecker.rb}
> 
> Then you want it to find these commands
> [
>   "echo \"if ARGV.empty? ; puts 'no args' else puts 'got args' end\" >
> argchecker.rb ",
>   " ruby argchecker.rb 1 2 3 ",
>   " ruby argchecker.rb"
> ]
> 
> But split(';') will give you these commands
> [
>   "echo \"if ARGV.empty? ",
>   " puts 'no args' else puts 'got args' end\" > argchecker.rb ",
>   " ruby argchecker.rb 1 2 3 ",
>   " ruby argchecker.rb"
> ]
> 
> 
> I think the best solution (easiest to implement, least likely to have 
> bugs,
> most straightforward) is to keep each command separated in the Array, 
> and
> not try to pull them from the string. If you do need to do that, you 
> must
> either be careful to avoid using a semicolon in a way that is not a 
> command
> delimiter, or you must find/write a parser so that you can determine 
> where
> commands begin and end. I suppose you could also pick a different 
> delimiter
> that is really unlikely to ever show up outside of the delimiter 
> context.
> Some obscure unicode character, maybe.

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