Linux Command Library


Interpreted object-oriented scripting language

- Open an Interactive Ruby Shell (REPL):

- Execute a Ruby script:
ruby [script.rb]

- Execute a single Ruby command in the command line:
ruby -e [command]

- Check for syntax errors on a given Ruby script:
ruby -c [script.rb]

- Show the version of Ruby you are using:
ruby -v

ruby [--copyright] [--version] [-Sacdlnpswvy] [-0[octal]] [-C directory] [-F pattern] [-I directory] [-K c] [-T[level]] [-e command] [-i[extension]] [-r library] [-x[directory]] [--] [program_file] [argument ...]

Ruby is an interpreted scripting language for quick and easy object-oriented programming. It has many features to process text files and to do system management tasks (as in Perl). It is simple, straight-forward, and extensible.

If you want a language for easy object-oriented programming, or you don't like the Perl ugliness, or you do like the concept of LISP, but don't like too much parentheses, Ruby may be the language of your choice.

Ruby's features are as follows:

Ruby is an interpreted language, so you don't have to recompile programs written in Ruby to execute them.

Variables have no type (dynamic typing) Variables in Ruby can contain data of any type. You don't have to worry about variable typing. Consequently, it has a weaker compile time check.

No declaration needed You can use variables in your Ruby programs without any declarations. Variable names denote their scope, local, global, instance, etc.

Simple syntax Ruby has a simple syntax influenced slightly from Eiffel.

No user-level memory management Ruby has automatic memory management. Objects no longer referenced from anywhere are automatically collected by the garbage collector built into the interpreter.

Everything is an object Ruby is the purely object-oriented language, and was so since its creation. Even such basic data as integers are seen as objects.

Class, inheritance, and methods Of course, as an object-oriented language, Ruby has such basic features like classes, inheritance, and methods.

Singleton methods Ruby has the ability to define methods for certain objects. For example, you can define a press-button action for certain widget by defining a singleton method for the button. Or, you can make up your own prototype based object system using singleton methods, if you want to.

Mix-in by modules Ruby intentionally does not have the multiple inheritance as it is a source of confusion. Instead, Ruby has the ability to share implementations across the inheritance tree. This is often called 'Mix-in'.

Iterators Ruby has iterators for loop abstraction.

Closures In Ruby, you can objectify the procedure.

Text processing and regular expression Ruby has a bunch of text processing features like in Perl.

Bignums With built-in bignums, you can for example calculate factorial(400).

Exception handling As in Java(tm).

Direct access to the OS Ruby can use most UNIX system calls, often used in system programming.

Dynamic loading On most UNIX systems, you can load object files into the Ruby interpreter on-the-fly.

Ruby interpreter accepts following command-line options (switches). They are quite similar to those of perl(1).

 --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 automaticline-ending processing, which means to firstly set $\ tothe value of $/, and secondly chops every line read usingchop!.
-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 ofvariable $_ at the each end of the loop. For example:
% echo matz | ruby -p -e '$! "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).

--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.

 RUBYLIB' A colon-separated list of directories that areadded to Ruby's library load path ($:). Directories fromthis environment variable are searched before thestandard load path is searched. e.g.: RUBYLIB="$HOME/lib/ruby:$HOME/lib/rubyext"
RUBYOPT' Additional Ruby options.

e.g. RUBYOPT="-w -Ke"

RUBYPATH' A colon-separated list of directories that Ruby searches for Ruby programs when the -S flag is specified. This variable precedes the PATH environment variable.

RUBYSHELL' The path to the system shell command. This environment variable is enabled for only mswin32, mingw32, and OS/2 platforms. If this variable is not defined, Ruby refers to COMSPEC.

PATH' Ruby refers to the PATH environment variable on calling Kernel#system.

RUBYLIB_PREFIX This variable is obsolete.

Ruby is designed and implemented by Yukihiro Matsumoto <>.

UNIX December 31, 2002 UNIX

kross(1), pdumpfs(8), shotgun(1), texexec(1), texmfstart(1)

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