Forum: Ruby Using Shell linux commands in Ruby!

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8250bc01c27651035e14905b2c5fe961?d=identicon&s=25 Ch Asif (muasif80)
on 2008-10-03 12:41
I have the following text that allows for having shell linux commands
executed and their results manipulated inside ruby code. If anyone can
tell me a better way of doing this, or he/she can mention the pros and
cons of this way of using shell linux commands inside ruby. I will be
very thankful to him/her. The following text is also available on the
link
http://linux-certification.blogspot.com/2008/10/us...

The following is a step by step guide how can you write shell linux
commands inside ruby code and get their results in customized output
created by ruby.


First of all execute the following command on shell prompt

shell> vi userinfo.rb

This will open up vi editor with a file named userinfo opened in it

1. Press i on your keyboard, this will switch the file userinfo into
insert mode
2. Write the following code in it



#Code Starts
def user
user = `users`
end

def groups
groups = `groups`
end

puts "You are #{user} and you belongs to the groups \n #{groups}"
#Code Ends

3. Press ESC key on your keyboard to exit insert mode
4. Now write :wq and press enter key on your keyboard

This will throw you out to the shell prompt. On the shell prompt write
the following command

shell> ruby userinfo.rb

You will the customized output like this

You are root and you belong to the groups
  [A list of group will be displayed on this line]

Thats it to executing shell linux commands inside your linux code
6a6d3bbc06625f2043bdb5d79fa8512b?d=identicon&s=25 geo ssscripting (vhaerun)
on 2008-10-03 12:50
pros and cons ?

pro would be that you can write your own version of a binary

con would be that a shell is spawned to execute the command

Another way to execute a command would be through the system method. But
then you couldn't get the command output that easily , since system
returns an exit code .
0026dd77fd9ecc97b36e5b79cdbcf590?d=identicon&s=25 R. Kumar (sentinel)
on 2008-10-03 13:13
Ch Asif wrote:
>

Please also look at: %x{command}

such as :

dirlist=%x{ls -m}

etc.

Do note that you may have to chomp() the result in many cases - there
will be the extra char at end (newline).

btw, system() won't return the output.

There are other variations such as "exec" which will overlay your
current process ...

 my favorite is %x{...}
Bc368ef524130e8d0deb386de961e24a?d=identicon&s=25 Suraj Kurapati (snk)
on 2008-10-03 19:06
Lex Williams wrote:
> Another way to execute a command would be through the system method.

See also IO#popen:

>> IO.popen('cat', 'w+') {|f| f << 'hello'; f.close_write; puts f.read }
hello
=> nil
>> puts $?.exitstatus
0
=> nil

> But then you couldn't get the command output that easily,
> since system returns an exit code .

Wrong.  Obtaining the output of a command has nothing to do with the
exit code:

>> `false`
=> ""
>> puts $?.exitstatus
1
=> nil
6a6d3bbc06625f2043bdb5d79fa8512b?d=identicon&s=25 geo ssscripting (vhaerun)
on 2008-10-03 19:18
> Wrong.  Obtaining the output of a command has nothing to do with the
> exit code:
>
>>> `false`
> => ""
>>> puts $?.exitstatus
> 1
> => nil

Interesting example of NOT using system .
D337e2cf7c6d03caac6988d83e0e7f66?d=identicon&s=25 Michael Guterl (Guest)
on 2008-10-03 19:50
(Received via mailing list)
On Fri, Oct 3, 2008 at 6:48 AM, Lex Williams <etaern@yahoo.com> wrote:
> pros and cons ?
>
> pro would be that you can write your own version of a binary
>
> con would be that a shell is spawned to execute the command
>
> Another way to execute a command would be through the system method. But
> then you couldn't get the command output that easily , since system
> returns an exit code .

Actually Kernel#system returns true or false

macbook:~ michaelguterl$ ri Kernel#system
---------------------------------------------------------- Kernel#system
     system(cmd [, arg, ...])    => true or false
6a6d3bbc06625f2043bdb5d79fa8512b?d=identicon&s=25 geo ssscripting (vhaerun)
on 2008-10-03 20:12
sorry , I thought ruby went along the same way as the other languages
about system.
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