--copyright    Prints the copyright notice.

--version      Prints the version of Ruby interpreter.

-0[octal]      (The digit “zero”.)  Specifies the input record separator ($/) as an octal number. If no
               digit is given, the null character is taken as the separator.  Other switches may follow the
               digits.  -00 turns Ruby into paragraph mode.  -0777 makes Ruby read whole file at once as a
               single string since there is no legal character with that value.

-C directory   Causes Ruby to switch to the directory.

-F pattern     Specifies input field separator ($;).

-I directory   Used to tell Ruby where to load the library scripts.  Directory path will be added to the
               load-path variable ($:).

-K kcode       Specifies KANJI (Japanese) encoding.

-S             Makes Ruby use the PATH environment variable to search for script, unless if its name begins
               with a slash.  This is used to emulate #! on machines that don't support it, in the
               following manner:

                     #! /usr/local/bin/ruby
                     # This line makes the next one a comment in Ruby \
                       exec /usr/local/bin/ruby -S $0 $*

-T[level]      Turns on taint checks at the specified level (default 1).

-a             Turns on auto-split mode when used with -n or -p.  In auto-split mode, Ruby executes
                     $F = $_.split
               at beginning of each loop.

-c             Causes Ruby to check the syntax of the script and exit without executing. If there are no
               syntax errors, Ruby will print “Syntax OK” to the standard output.

-d
--debug        Turns on debug mode.  $DEBUG will be set to true.

-e command     Specifies script from command-line while telling Ruby not to search the rest of arguments
               for a script file name.

-h
--help         Prints a summary of the options.

-i extension   Specifies in-place-edit mode.  The extension, if specified, is added to old file name to
               make a backup copy.  For example:

                     % echo matz > /tmp/junk
                     % cat /tmp/junk
                     matz
                     % ruby -p -i.bak -e '$_.upcase!' /tmp/junk
                     % cat /tmp/junk
                     MATZ
                     % cat /tmp/junk.bak
                     matz

-l             (The lowercase letter “ell”.)  Enables automatic line-ending processing, which means to
               firstly set $\ to the value of $/, and secondly chops every line read using chop!.

-n             Causes Ruby to assume the following loop around your script, which makes it iterate over
               file name arguments somewhat like sed -n or awk.

                     while gets
                       ...
                     end

-p             Acts mostly same as -n switch, but print the value of variable $_ at the each end of the
               loop.  For example:

                     % echo matz | ruby -p -e '$_.tr! "a-z", "A-Z"'
                     MATZ

-r library     Causes Ruby to load the library using require.  It is useful when using -n or -p.

-s             Enables some switch parsing for switches after script name but before any file name
               arguments (or before a --).  Any switches found there are removed from ARGV and set the
               corresponding variable in the script.  For example:

                     #! /usr/local/bin/ruby -s
                     # prints "true" if invoked with `-xyz' switch.
                     print "true\n" if $xyz

               On some systems $0 does not always contain the full pathname, so you need the -S switch to
               tell Ruby to search for the script if necessary.  To handle embedded spaces or such.  A
               better construct than $* would be ${1+"$@"}, but it does not work if the script is being
               interpreted by csh(1).

-v
--verbose      Enables verbose mode.  Ruby will print its version at the beginning, and set the variable
               $VERBOSE to true.  Some methods print extra messages if this variable is true.  If this
               switch is given, and no other switches are present, Ruby quits after printing its version.

-w             Enables verbose mode without printing version message at the beginning.  It sets the
               $VERBOSE variable to true.

-x[directory]  Tells Ruby that the script is embedded in a message.  Leading garbage will be discarded
               until the first that starts with “#!” and contains the string, “ruby”.  Any meaningful
               switches on that line will applied.  The end of script must be specified with either EOF, ^D
               (control-D), ^Z (control-Z), or reserved word __END__.  If the directory name is specified,
               Ruby will switch to that directory before executing script.

-y
--yydebug      Turns on compiler debug mode.  Ruby will print a bunch of internal state messages during
               compiling scripts.  You don't have to specify this switch, unless you are going to debug the
               Ruby interpreter.