How to Pass <Arguments> to Irb If I Don't Specify <Programfile>

Reset IRB Console

Type

exec($0)

in your irb console session.

How to require files by default without mentioning explicitly

Ruby 1.9 help:

$ ruby --help
Usage: ruby [switches] [--] [programfile] [arguments]
  -0[octal]       specify record separator (\0, if no argument)
  -a              autosplit mode with -n or -p (splits $_ into $F)
  -c              check syntax only
  -Cdirectory     cd to directory, before executing your script
  -d              set debugging flags (set $DEBUG to true)
  -e 'command'    one line of script. Several -e's allowed. Omit [programfile]
  -Eex[:in]       specify the default external and internal character encodings
  -Fpattern       split() pattern for autosplit (-a)
  -i[extension]   edit ARGV files in place (make backup if extension supplied)
  -Idirectory     specify $LOAD_PATH directory (may be used more than once)
  -l              enable line ending processing
  -n              assume 'while gets(); ... end' loop around your script
  -p              assume loop like -n but print line also like sed
  -rlibrary       require the library, before executing your script
  -s              enable some switch parsing for switches after script name
  -S              look for the script using PATH environment variable
  -T[level=1]     turn on tainting checks
  -v              print version number, then turn on verbose mode
  -w              turn warnings on for your script
  -W[level=2]     set warning level; 0=silence, 1=medium, 2=verbose
  -x[directory]   strip off text before #!ruby line and perhaps cd to directory
  --copyright     print the copyright
  --version       print the version

Take a look on:

-rlibrary       require the library, before executing your script

Why is the --simple-prompt command not working?

You seem to be confused about passing flags to commands vs issuing statements in a REPL.

To start irb with the --simple-prompt option enabled, pass it in like so:

$ irb --simple-prompt
>>

Then you should be able to execute Ruby code.

>> puts "hello world!"
hello world!
=> nil
>>

Couldn't understand how the command line option -T is used in practice

It sets the $SAFE level.

This dictates how inputs are handled, along with a great number of other things regarding environment variables, I/O, threads, exceptions, interpreter command line args, etc.

http://www.ruby-doc.org/docs/ProgrammingRuby/html/taint.html

IMO the docs are a good place to start. If you have a question about a specific behavior, ask.

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To address your comment and your edits:

Yes, I can, but the docs can too, and likely better.

Why does -x not work?

Because the docs say it won't:

$SAFE >= 1

   * The command-line options -e, -i, -I, -r, -s, -S, and -x are not allowed.

[~]$ ruby --help
Usage: ruby [switches] [--] [programfile] [arguments]
# elided
-T[level=1] turn on tainting checks

So the default level if -T is specified with no number is 1, which means $SAFE >= 1, which means exactly what the docs say: -x is not allowed.

Why doesn't puts work?

Difficult to say since you don't actually provide the code you're executing, but most likely, again, as the docs say:

$SAFE >= 4

   * Can't write to files or pipes.

which in ruby: Checking if program exists in $PATH from ruby

True cross-platform solution, works properly on Windows:

# Cross-platform way of finding an executable in the $PATH.
#
#   which('ruby') #=> /usr/bin/ruby
def which(cmd)
  exts = ENV['PATHEXT'] ? ENV['PATHEXT'].split(';') : ['']
  ENV['PATH'].split(File::PATH_SEPARATOR).each do |path|
    exts.each do |ext|
      exe = File.join(path, "#{cmd}#{ext}")
      return exe if File.executable?(exe) && !File.directory?(exe)
    end
  end
  nil
end

This doesn't use host OS sniffing, and respects $PATHEXT which lists valid file extensions for executables on Windows.

Shelling out to which works on many systems but not all.

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