Module: RIO::Doc::INTRO

Defined in:

lib/rio/doc/INTRO.rb

Overview

Rio - Ruby I/O Comfort Class

Rio is a convenience class wrapping much of the functionality of IO, File, Dir, Pathname, FileUtils, Tempfile, StringIO, and OpenURI and uses Zlib, and CSV to extend that functionality using a simple consistent interface. Most of the instance methods of IO, File and Dir are simply forwarded to the appropriate handle to provide identical functionality. Rio also provides a “grande” interface that allows many application level IO tasks to be expressed succinctly.

Rio functionality can be broadly broken into three categories

• path manipulation

• file system access

• stream manipulation

Which methods are available to a given Rio, depends on the underlying object.

A Rio generally does not need to be opened or have its mode specified. Most of Rio’s methods simply configure it. When an actual IO operation is specified, Rio determines how to open it based on the object it is opening, the operation it is performing, and the options specified.

Rio configuration methods return the Rio for easy chaining and regard the presence of a block as an implied each.

Using a Rio

Using a Rio can be described as having 3 steps:

• Creating a Rio

• Configuring a Rio

• Rio I/O

Creating a Rio

Rio extends Kernel with one function rio, its constructor. This function is overloaded to create any type of Rio. rio looks at the class and sometimes the value of its first argument to create an internal representation of the resource specified, additional arguments are used as needed by the resource type. The rio constructor does not initiate any io, it does not check for a resources existance or type. It neither knows nor cares what can be done with this Rio. Using methods like respond_to? are meaningless at best and usually misleading.

For purposes of discussion, we divide Rios into two catagories, those that have a path and those that don’t.

Creating a Rio that has a path

To create a Rio that has a path the arguments to rio may be:

• a string representing the entire path. The separator used for Rios is as specified in RFC1738 (‘/’).

  rio('adir/afile')
  

• a string representing a fully qualified file URI as per RFC1738

  rio('file:///atopleveldir/adir/afile')
  

• a URI object representing a file or generic URI

  rio(URI('adir/afile'))
  

• the components of a path as separate arguments

  rio('adir','afile')
  

• the components of a path as an array

  rio(%w/adir afile/)
  

• another Rio

  another_rio = rio('adir/afile')
  rio(another_rio)
  

• any object whose to_s method returns one of the above

  rio(Pathname.new('apath'))
  

• any combination of the above either as separate arguments or as elements of an array,

  another_rio = rio('dir1/dir2')
  auri = URI('dir4/dir5)
  rio(another_rio,'dir3',auri,'dir6/dir7')
  

Creating a Rio that refers to a web page

To create a Rio that refers to a web page the arguments to rio may be:

• a string representing a fully qualified http URI

  rio('http://ruby-doc.org/index.html')
  

• a URI object representing a http URI

  rio(URI('http://ruby-doc.org/index.html'))
  

• either of the above with additional path elements

  rio('http://www.ruby-doc.org/','core','classes/Object.html')
  

Creating a Rio that refers to a file or directory on a FTP server

To create a Rio that refers to a file on a FTP server the arguments to rio may be:

• a string representing a fully qualified ftp URI

  rio('ftp://user:password@ftp.example.com/afile.tar.gz')
  

• a URI object representing a ftp URI

  rio(URI('ftp://ftp.example.com/afile.tar.gz'))
  

• either of the above with additional path elements

  rio('ftp://ftp.gnu.org/pub/gnu','emacs','windows','README')
  

Creating Rios that do not have a path

To create a Rio without a path, the first argument to rio is usually a single character.

Creating a Rio that refers to a clone of your programs stdin or stdout.

rio(?-) (mnemonic: ‘-’ is used by some Unix programs to specify stdin or stdout in place of a file)

Just as a Rio that refers to a file, does not know whether that file will be opened for reading or writing until an io operation is specified, a stdio: Rio does not know whether it will connect to stdin or stdout until an I/O operation is specified.

Creating a Rio that refers to a clone of your programs stderr.

rio(?=) (mnemonic: ‘-’ refers to fileno 1, so ‘=’ refers to fileno 2)

Creating a Rio that refers to an arbitrary IO object.

an_io = ::File.new('afile')
rio(an_io)

Creating a Rio that refers to a file descriptor

rio(?#,fd) (mnemonic: a file descriptor is a number ‘#’ )

an_io = ::File.new('afile')
rio(an_io)

Creating a Rio that refers to a StringIO object

rio(?") (mnemonic: ‘“’ surrounds strings)

• create a Rio that refers to its own string

rio(?")

• create a Rio that refers to a string of your choosing

astring = ""
rio(?",astring)

Creating a Rio that refers to a Temporary object

rio(??) (mnemonic: ‘?’ you don’t know its name)

To create a temporary object that will become a file or a directory, depending on how you use it:

rio(??)
rio(??,basename='rio',tmpdir=Dir::tmpdir)

To force it to become a directory:

rio(??).mkdir

or

rio(??).chdir

Creating a Rio that refers to an arbitrary TCPSocket

rio('tcp:',hostname,port)

or

rio('tcp://hostname:port')

Creating a Rio that runs an external program and connects to its stdin and stdout

rio(?-,cmd) (mnemonic: ‘-’ is used by some Unix programs to specify stdin or stdout in place of a file)

or

rio(?`,cmd) (mnemonic: ‘`’ (backtick) runs an external program in ruby)

This is Rio’s interface to IO#popen

Path Manipulation

Rio’s path manipulation methods are for the most part simply forwarded to the File or URI classes with the return values converted to a Rio.

Creating a Rio from a Rio’s component parts.

The Rio methods for creating a Rio from a Rio’s component parts are IF::Path#dirname, IF::Path#filename, IF::Path#basename, and IF::Path#extname. The behavior of IF::Path#basename depends on the setting of the ext configuration variable and is different from its counterpart in the File class. The default value of the ext configuration variable is the string returned File#extname. The ext configuration variable can be changed using IF::Path#ext and IF::Path#noext and can be queried using IF::Path#ext?. This value is used by calls to IF::Path#basename.

IF::Path#filename returns the last component of a path, and is basically the same as basename without consideration of an extension.

rio('afile.txt').basename       #=> rio('afile')
rio('afile.txt').filename       #=> rio('afile.txt')

ario = rio('afile.tar.gz')
ario.basename                   #=> rio('afile.tar')
ario.ext?                       #=> ".gz"
ario.ext('.tar.gz').basename    #=> rio('afile')
ario.ext?                       #=> ".tar.gz"

Changing a path’s component parts.

Rio also provides methods for changing the component parts of its path. They are IF::Path#dirname=, IF::Path#filename=, IF::Path#basename=, and IF::Path#extname=. These methods replace the part extracted as described above with their argument.

ario = rio('dirA/dirB/afile.rb')
ario.dirname = 'dirC'          # rio('dirC/afile.rb')
ario.basename = 'bfile'        # rio('dirC/bfile.rb')
ario.extname = '.txt'          # rio('dirC/bfile.txt')
ario.filename = 'cfile.rb'     # rio('dirC/cfile.rb')

Rio also has a rename mode which causes each of these to rename the actual file system object as well as changing the Rio. This is discussed in the section on Renaming and Moving.

Splitting a Rio

IF::Grande#split (or IF::Path#splitpath) returns an array of Rios, one for each path element. (Note that this behavior differs from File#split.)

rio('a/b/c').split   #=> [rio('a'),rio('b'),rio('c')]

The array returned is extended with a to_rio method, which will put the parts back together again.

ary = rio('a/b/c').split   #=> [rio('a'),rio('b'),rio('c')]
ary.to_rio           #=> rio('a/b/c')

Creating a Rio by specifying the individual parts of its path

The first way to create a Rio by specifying its parts is to use the Rio constructor Rio#rio. Since a Rio is among the arguments the constructor will take, the constructor can be used.

ario = rio('adir')
rio(ario,'b')    #=> rio('adir/b')

IF::Path#join and IF::Path#/ do the same thing, but the operator version / can take only one argument.

a = rio('a')
b = rio('b')
c = a.join(b)    #=> rio('a/b')
c = a/b          #=> rio('a/b')

The arguments to IF::Path#join and IF::Path#/ do not need to be Rios, of course

ario = rio('adir')
ario/'afile.rb'           #=> rio('adir/afile.rb')
ario.join('b','c','d')    #=> rio('adir/b/c/d')
ario/'b'/'c'/'d'          #=> rio('adir/b/c/d')
ario /= 'e'               #=> rio('adir/b/c/d/e')

Manipulating a Rio path by treating it as a string.

The Rio methods which treat a Rio as a string are IF::String#sub, IF::String#gsub and IF::String#+. These methods create a new Rio using the string created by forwarding the method to the String returned by Rio#to_s.

ario = rio('dirA/dirB/afile') + '-1.1.1'   # rio('dirA/dirB/afile-1.1.1')
brio = ario.sub(/^dirA/, 'dirC')           # rio('dirC/dirB/afile-1.1.1')

Creating a Rio based on its relationship to another

IF::Path#abs creates a new rio whose path is the absolute path of a Rio. If called with an argument, it uses it as the base path, otherwise it uses an internal base path (usually the current working directory when it was created).

rio('/tmp').chdir do
  rio('a').abs            #=> rio('/tmp/a')
  rio('a').abs('/usr')    #=> rio('/usr/a')
end

IF::Path#rel creates a new rio with a path relative to a Rio.

rio('/tmp').chdir do
  rio('/tmp/a').rel       #=> rio('a')
end
rio('/tmp/b').rel('/tmp') #=> rio('b')

IF::Path#route_to and IF::Path#route_from creates a new rio with a path representing the route to get to/from a Rio. They are based on the methods of the same names in the ::URI class

Configuring a Rio

The second step in using a rio is configuring it. Note that many times no configuration is necessary and that this is not a comprehensive list of all of Rio’s configuration methods.

Rio’s configuration mehods fall into three categories.

• I/O manipulators

  An I/O manipulator alters the behavior of a Rio’s underlying IO object. These affect the behaviour of I/O methods which are forwarded directly to the underlying object as well as the grande I/O methods.

• Grande configuration methods

  The grande configuration methods affect the behaviour of Rio’s grande I/O methods

• Grande selection methods

  The grande selection methods select what data is returned by Rio’s grande I/O methods

All of Rio’s configuration and selection methods can be passed a block, which will cause the Rio to behave as if IF::Grande#each had been called with the block after the method.

IO manipulators

• gzip a file on output, and ungzip it on input

  rio('afile.gz').gzip
  

  This causes the rio to read through a Zlib::GzipReader and to write Zlib::GzipWriter.

• chomp lines as they are read

  rio('afile').chomp
  

  This causes a Rio to call String#chomp on the the String returned by all line oriented read operations.

Grande configuration methods

• all, recurse, norecurse

  rio('adir').all
  rio('adir').norecurse('CVS')
  

  These methods instruct the Rio to also include entries in subdirectories when iterating through directories and control which subdirectories are included or excluded.

• bytes

  rio('afile').bytes(1024)
  

  This causes a Rio to read the specified number of bytes at a time as a file is iterated through.

Grande selection methods

• lines, skiplines

  rio('afile').lines(0..9)
  rio('afile').skiplines(/^\s*#/)
  

  Strictly speaking these are both configuration and selection methods. They configure the Rio to iterate through an input stream as lines. The arguments select which lines are actually returned. Lines are included (lines) or excluded (skiplines) if they match any of the arguments as follows.

  If the argument is a:

  RegExp

  the line is matched against it

  Range

  the lineno is matched against it

  Integer

  the lineno is matched against it as if it were a one element range

  Symbol

  the symbol is sent to the string; the line is included unless it returns false

  Proc

  the proc is called with the line as an argument; the line is included unless it returns false

  Array

  an array containing any of the above, all of which must match for the line to be included

• entries, files, dirs, skipentries, skipfiles, skipdirs

  rio('adir').files('*.txt')
  rio('adir').skipfiles(/^\./)
  

  These methods select which entries will be returned when iterating throug directories. Entries are included (entries,files,dirs) or excluded(skipentries,skipfiles,skipdirs) if they match any of the arguments as follows.

  If the argument is a:

  String

  the arg is treated as a glob; the filname is matched against it

  RegExp

  the filname is matched against it

  Symbol

  the symbol is sent to the entry (a Rio); the entry is included unless it returns false

  Proc

  the proc is called with the entry (a Rio) as an argument; the entry is included unless it returns false

  Array

  an array containing any of the above, all of which must match for the line to be included

• records, rows, skiprecords, skiprows

  rio('afile').bytes(1024).records(0...10)
  

  These select items from an input stream just as lines, but without specifying lines as the input record type. They can be used to select different record types in extension modules. The only such module at this writing is the CSV extension. In that case records causes each line of a CSV file to be parsed into an array while lines causes each line of the file to be returned normally.

Rio I/O

As stated above the the three steps to using a Rio are:

• Creating a Rio

• Configuring a Rio

• Doing I/O

This section describes that final step.

After creating and configuring a Rio, the file-system has not been accessed, no socket has been opened, not so much as a test for a files existance has been done. When an I/O method is called on a Rio, the sequence of events required to complete that operation on the underlying object takes place. Rio takes care of creating the appropriate object (eg IO,Dir), opening the object with the appropriate mode, performing the operation, closing the object if required, and returning the results of the operation.

Rio’s I/O operations can be divide into two catagories:

• Proxy operations

• Grande operations

Proxy operations

These are calls which are forwarded to the underlying object (eg IO,Dir,Net::FTP), after appropriately creating and configuring that object. The result produced by the method is returned, and the object is closed.

In some cases the result is modified before being returned, as when a Rio is configured with IF::GrandeStream#chomp.

In all cases, if the result returned by the underlying object, could itself be used for further I/O operations it is returned as a Rio. For example: where File#dirname returns a string, IF::Path#dirname returns a Rio; where Dir#read returns a string representing a directory entry, IF::FileOrDir#read returns a Rio.

With some noteable exceptions, most of the operations available if one were using the underlying Ruby I/O class are available to the Rio and will behave identically.

For things that exist on a file system:

• All the methods in FileTest are available as Rio instance methods. For example

  FileTest.file?('afile')
  

  becomes

  rio('afile').file?
  

• All the instance methods of File except path are available to a rio without change

• Most of the class methods of File are available.

  • For those that take a filename as their only argument the calls are mapped to Rio instance methods as described above for FileTest.

  • dirname, and readlink return Rios instead of strings

  • Rio has its own IF::Path#basename, IF::Path#join and IF::FileOrDir#symlink, which provide similar functionality.

  • The class methods which take multiple filenames (chmod,chown,lchmod,lchown) are available as Rio instance methods. For example

    File.chmod(0666,'afile')
    

    becomes

    rio('afile').chmod(06660)
    

For I/O Streams

Most of the instance methods of IO are available, and most do the same thing, with some interface changes. The big exception to this is the ‘<<’ operator. This is one of Rio’s grande operators. While the symantics one would use to write to an IO object would actually accomplish the same thing with a Rio, It is a very different operator. Read the section on grande operators. The other differences between IO instance methods and the Rio equivelence can be summarized as follows.

• The simple instance methods (eg fcntl, eof?, tty? etc.) are forwarded and the result returned as is

• Anywhere IO returns an IO, Rio returns a Rio

• close and its cousins return the Rio.

• each_byte and each_line are forwarded as is.

• All methods which read (read*,get*,each*) will cause the file to closed when the end of file is reached. This behavior is configurable, but the default is to close on eof

• The methods which write (put*,print*) are forwarded as is; put* and print* return the Rio; write returns the value returned by IO#write; as mentioned above ‘<<’ is a grande operator in Rio.

For directories:

• all the instance methods of Dir are available except each which is a grande method.

• the class methods mkdir, delete, rmdir are provided as instance methods.

• chdir is provided as an instance method. IF::Dir#chdir returns a Rio and passes a Rio to a block if one is provided.

• glob is provided as an instance method, but returns an array of Rios

• foreach is not supported

• each and [] have similar functionality provided by Rio

For other Rios, instance methods are generally forwarded where appropriate. For example

• Rios that refer to StringIO objects forward ‘string’ and ‘string=’

• Rios that refer to http URIs support all the Meta methods provided by open-uri

Grande operators

The primary grande operator is IF::Grande#each. each is used to iterate through Rios. When applied to a file it iterates through records in the file. When applied to a directory it iterates through the entries in the directory. Its behavior is modified by configuring the Rio prior to calling it using the configuration methods discussed above. Since iterating through things is ubiquitous in ruby, it is implied by the presence of a block after any of the grande configuration methods and many times does not need to be call explicitly. For example:

# iterate through chomped ruby comment lines
rio('afile.rb').chomp.lines(/^\s*#/) { |line| ... } 

# iterate through all .rb files in 'adir' and its subdirectories
rio('adir').all.files('*.rb') { |f| ... }

Because a Rio is an Enumerable, it supports to_a, which is the basis for the grande subscript operator. IF::Grande#[] with no arguments simply calls to_a. With arguments it behaves as if those arguments had been passed to the most recently called of the grande selection methods listed above, and then calls to_a. For example to get the first ten lines of a file into an array with lines chomped

rio('afile').chomp.lines(0...10).to_a

can be written as

rio('afile.gz').chomp.lines[0...10]

or, to create an array of all the .c files in a directory, one could write

rio('adir').files['*.c']

The other grande operators are its copy operators. They are:

• < (copy-from)

• << (append-from)

• > (copy-to)

• >> (append-to)

The only difference between the ‘copy’ and ‘append’ versions is how they deal with an unopened resource. In the former the open it with mode ‘w’ and in the latter, mode ‘a’. Beyond that, their behavior can be summarized as:

source.each do |entry|
  destination << entry
end

Since they are based on the each operator, all of the selection and configuration options are available. And the right-hand-side argument of the operators are not restricted to Rios – Strings and Arrays are also supported.

For example:

rio('afile') > astring # copy a file into a string

rio('afile').chomp > anarray # copy the chomped lines of afile into an array

rio('afile.gz').gzip.lines(0...100) > rio('bfile') # copy 100 lines from a gzipped file into another file

rio(?-) < rio('http://rubydoc.org/') # copy a web page to stdout

rio('bdir') < rio('adir') # copy an entire directory structure

rio('adir').dirs.files('README') > rio('bdir') # same thing, but only README files

rio(?-,'ps -a').skiplines(0,/ps$/) > anarray # copy the output of th ps command into an array, skippying
                                           # the header line and the ps command entry

Renaming and Moving

Rio provides two methods for directly renaming objects on the filesystem: IF::FileOrDir#rename and IF::FileOrDir#rename!. Both of these use File#rename. The difference between them is the returned Rio. IF::FileOrDir#rename leaves the path of the Rio unchanged, while IF::FileOrDir#rename! changes the path of the Rio to refer to the renamed path.

ario = rio('a')
ario.rename('b')  # file 'a' has been renamed to 'b' but 'ario' => rio('a')
ario.rename!('b')  # file 'a' has been renamed to 'b' and 'ario' => rio('b')

Rio also has a rename mode, which causes the path manipulation methods IF::Path#dirname=, IF::Path#filename=, IF::Path#basename= and IF::Path#extname= to rename an object on the filesystem when they are used to change a Rio’s path. A Rio is put in rename mode by calling IF::FileOrDir#rename with no arguments.

rio('adir/afile.txt').rename.filename = 'bfile.rb' # adir/afile.txt => adir/bfile.rb
rio('adir/afile.txt').rename.basename = 'bfile'    # adir/afile.txt => adir/bfile.txt
rio('adir/afile.txt').rename.extname  = '.rb'      # adir/afile.txt => adir/afile.rb
rio('adir/afile.txt').rename.dirname =  'b/c'      # adir/afile.txt => b/c/afile.txt

When rename mode is set for a directory Rio, it is automatically set in the Rios created when iterating through that directory.

rio('adir').rename.files('*.htm') do |frio|
   frio.extname = '.html'  #=> changes the rio and renames the file
end

Deleting

The Rio methods for deleting filesystem objects are IF::File#rm, IF::Dir#rmdir, IF::Dir#rmtree, IF::Grande#delete, and IF::Grande#delete!. rm, rmdir and rmtree are passed the like named methods in the FileUtils module. IF::Grande#delete calls rmdir for directories and rm for anything else, while IF::Grande#delete! calls IF::Dir#rmtree for directories.

• To delete something only if it is not a directory use IF::File#rm

• To delete an empty directory use IF::Dir#rmdir

• To delete an entire directory tree use IF::Dir#rmtree

• To delete anything except a populated directory use IF::Grande#delete

• To delete anything use IF::Grande#delete!

It is not an error to call any of the deleting methods on something that does not exist. Rio provides IF::Test#exist? and IF::Test#symlink? to check if something exists (exist? returns false for symlinks to non-existant object even though the symlink itself exists). The deleting methods’ purpose is to make things not exist, so calling one of them on something that already does not exist is considered a success.

To create a clean copy of a directory whether or not anything with that name exists one might do this

rio('adir').delete!.mkpath.chdir do
  # do something in adir
end

---

Miscellany

Using Symbolic Links

To create a symbolic link (symlink) to the file-system entry refered to by a Rio, use IF::FileOrDir#symlink. IF::FileOrDir#symlink differs from File#symlink in that it calculates the path from the symlink location to the Rio’s position.

File#symlink('adir/afile','adir/alink')

creates a symlink in the directory ‘adir’ named ‘alink’ which references ‘adir/afile’. From the perspective of ‘alink’, ‘adir/afile’ does not exist. While:

rio('adir/afile').symlink('adir/alink')

creates a symlink in the directory ‘adir’ named ‘alink’ which references ‘afile’. This is the route to ‘adir/afile’ from the perspective of ‘adir/alink’.

Note that the return value from symlink is the calling Rio and not a Rio refering to the symlink. This is done for consistency with the rest of Rio.

IF::Test#symlink? can be used to test if a file-system object is a symlink. A Rio is extended with IF::FileOrDir#readlink, and IF::Test#lstat only if IF::Test#symlink? returns true. So for non-symlinks, these will raise a NoMethodError. These are both passed to their counterparts in File. IF::FileOrDir#readlink returns a Rio refering to the result of File#readlink.

Using A Rio as an IO (or File or Dir)

Rio supports so much of IO’s interface that one might be tempted to pass it to a method that expects an IO. While Rio is not and is not intended to be a stand in for IO, this can work. It requires knowledge of every IO method that will be called, under any circumstances.

Even in cases where Rio supports the required IO interface, A Rio feature that seems to cause the most incompatibility, is its automatic closing of files. To turn off all of Rio’s automatic closing use IF::GrandeStream#noautoclose.

For example:

require 'yaml'
yrio = rio('ran.yaml').delete!.noautoclose
YAML.dump( ['badger', 'elephant', 'tiger'], yrio )
obj = YAML::load( yrio ) #=> ["badger", "tiger", "elephant"]

Automatically Closing Files

Rio closes files automatically in three instances.

When reading from an IO it is closed when the end of file is reached. While this is a reasonable thing to do in many cases, sometimes this is not desired. To turn Rio’s automatic closing on end of file use IF::GrandeStream#nocloseoneof (it can be turned back on via IF::GrandeStream#closeoneof)

ario = rio('afile').nocloseoneof
lines = ario[]
ario.closed?   #=> false

Closing on end-of-file is necessary for many of Rio’s one-liners, but has an implication that may be surprising at first. A Rio starts life as a path, not much more than a string. When one of its read methods is called it becomes an input stream. When the stream is closed, it becomes a path again. This means that when reading from a Rio, the end-of-file condition is seen only once before it becomes a path again, and will be reopened if another read operation is attempted.

Another time a Rio will be closed atomatically is when writing to it with one of the copy operators (<, <<, >, >>). This behavior can be turned off with IF::GrandeStream#nocloseoncopy.

To turn off both of thes types of automatic closing use IF::GrandeStream#noautoclose.

The third instance when Rio will close a file automatically is when a file opened for one type of access receives a method which that access mode does not support. So, the code

rio('afile').puts("Hello World").gets

will open the file for write access when the puts method is received. When gets is called the file is closed and reopened with read access.

Explicitly Closing Files

Rio can not determine when the client is finished writing to it, as it does using eof on read. It is the author’s understanding that Ruby does not support a mechanism to have code run when there are no more references to it – that finalizers are not necessarily run immediatly upon an object’s reference count reaching 0. If this understanding is incorrect, some of Rio’s extranious ways of closing a file may be rethought.

That being said, Rio support several ways to explicitly close a file. IF::RubyIO#close will close any open Rio. The output methods IF::RubyIO#puts!, IF::RubyIO#putc!, IF::RubyIO#printf!, IF::RubyIO#print!, and IF::RubyIO#write!

behave as if their counterparts without the exclamation point had been called and then call IF::RubyIO#close or IF::RubyIO#close_write if the underlying IO object is opened for duplex access.

Open mode selection

A Rio is typically not explicitly opened. It opens a file automatically when an input or output methed is called. For output methods Rio opens a file with mode ‘w’, and otherwise opens a file with mode ‘r’. This behavior can be modified using the tersely named methods IF::GrandeStream#a, IF::GrandeStream#a!, IF::GrandeStream#r, IF::GrandeStream#r!, IF::GrandeStream#w, and IF::GrandeStream#w!, which cause the Rio to use modes ‘a’,‘a+’,‘r’,‘r+’,‘w’,and ‘w+’ respectively.

One way to append a string to a file and close it in one line is

rio('afile').a.puts!("Hello World")

Run a cmd that must be opened for read and write

ans = rio(?-,'cat').w!.puts!("Hello Kitty").readlines

The automatic selection of mode can be bypassed entirely using IF::RubyIO#mode and IF::FileOrDir#open.

If a mode is specified using mode, the file will still be opened automatically, but the mode specified in the mode method will be used regardless of whether it makes sense.

A Rio can also be opened explicitly using IF::RubyIO#open. open takes one parameter, a mode. This also will override all of Rio’s automatic mode selection.

CSV mode

Rio uses the CSV class from the Ruby standard library to provide support for reading and writing comma-separated-value files. Normally using (skip)records is identical to (skip)lines because while records only selects and does not specify the record-type, lines is the default.

rio('afile').records(1..2)

effectively means

rio('afile').lines.records(1..2)

The CSV extension distingishes between items selected using IF::GrandeStream#records and those selected using IF::GrandeStream#lines. Rio returns records parsed into Arrays by the CSV library when records is used, and returns Strings as normal when lines is used. records is the default.

rio('f.csv').puts!(["h0,h1","f0,f1"])                 

rio('f.csv').csv.records[]    #==>[["h0", "h1"], ["f0", "f1"]]
rio('f.csv').csv[]            #==> same thing
rio('f.csv').csv.lines[]      #==>["h0,h1\n", "f0,f1\n"]
rio('f.csv').csv.records[0]   #==>[["h0", "h1"]]
rio('f.csv').csv[0]           #==> same thing
rio('f.csv').csv.lines[0]     #==>["h0,h1\n"]
rio('f.csv').csv.skiprecords[0] #==>[["f0", "f1"]]
rio('f.csv').csv.skiplines[0]   #==>["f0,f1\n"]

This distinction, of course, applies equally when using the copy operators and each

rio('f.csv').csv[0] > rio('out').csv # out contains "f0,f1\n"

rio('f.csv').csv { |array_of_fields| ... }

Notice that csv mode is called on both the input and output Rios. The csv on the ‘out’ Rio causes it to treat an array written to it as an array of records which is converted into CSV format before writing. Without the csv, the output would be written as if Array#to_s on [[“f0”,“f1”]] had been called

rio('f.csv').csv[0] > rio('out') # out contains "f0f1"

The String representing a record that is returned when using lines is extended with a to_a method which will parse it into an array of fields. Likewise the Array returned when a record is returned using records is extended with a modified to_s which treats it as an array CSV fields, rather than just an array of strings.

array_of_lines = rio('f.csv').csv.lines[1]      #==>["f0,f1\n"]
array_of_records = rio('f.csv').csv.records[1]  #==>[["f0", "f1"]]

array_of_lines[0].to_a                          #==>["f0", "f1"]
array_of_records[0].to_s                        #==>"f0,f1"

IF::CSV#csv takes two optional parameters, which are passed on to the CSV library. They are the field_separator and the record_separator.

rio('semisep').puts!(["h0;h1","f0;f1"])                 

rio('semisep').csv(';').to_a  #==>[["h0", "h1"], ["f0", "f1"]]

These are specified independently on the source and destination when using the copy operators.

rio('semisep').csv(';') > rio('colonsep').csv(':')
rio('colonsep').contents  #==>"h0:h1\nf0:f1\n"

Rio provides two methods for selecting fields from CSV records in a manner similar to that provided for selecting lines – IF::CSV#columns and IF::CSV#skipcolumns.

rio('f.csv').puts!(["h0,h1,h2,h3","f0,f1,f2,f3"])

rio('f.csv').csv.columns(0).to_a       #==>[["h0"], ["f0"]]
rio('f.csv').csv.skipcolumns(0).to_a     #==>[["h1", "h2", "h3"], ["f1", "f2", "f3"]]
rio('f.csv').csv.columns(1..2).to_a    #==>[["h1", "h2"], ["f1", "f2"]]
rio('f.csv').csv.skipcolumns(1..2).to_a  #==>[["h0", "h3"], ["f0", "f3"]]

IF::CSV#columns can, of course be used with the each and the copy operators:

rio('f.csv').csv.columns(0..1) > rio('out').csv
rio('out').contents  #==>"h0,h1\nf0,f1\n"

YAML mode

Rio uses the YAML class from the Ruby standard library to provide support for reading and writing YAML files. Normally using (skip)records is identical to (skip)lines because while records only selects and does not specify the record-type, lines is the default.

The YAML extension distingishes between items selected using IF::GrandeStream#records, IF::GrandeStream#rows and IF::GrandeStream#lines. Rio returns objects loaded via YAML#load when records is used; returns the YAML text as a String when rows is used; and returns lines as Strings as normal when lines is used.

records is the default. In yaml-mode, (skip)records can be called as (skip)objects and (skip)rows can be called as (skip)documents

To read a single YAML document, Rio provides #getobj and #load For example, consider the following partial ‘database.yml’ from the rails distribution:

development:
  adapter: mysql
  database: rails_development

test:
  adapter: mysql
  database: rails_test

To get the object represented in the yaml file:

rio('database.yml').yaml.load
   ==>{"development"=>{"adapter"=>"mysql", "database"=>"rails_development"}, 
       "test"=>{"adapter"=>"mysql", "database"=>"rails_test"}}

Or one could read parts of the file like so:

rio('database.yml').yaml.getobj['development']['database']
   ==>"rails_development"

Single objects can be written using #putobj and #putobj! which is aliased to #dump

anobject = {
  'production' => {
    'adapter' => 'mysql',
    'database' => 'rails_production',
  }
}
rio('afile.yaml').yaml.dump(anobject)

IF::Grande#> (copy-to) and IF::Grande#>> (append-to) will fill an array with with all selected YAML documents in the Rio. For non-arrays, the yaml text is copied. (This may change if a useful reasonable alternative can be found)

rio('afile.yaml').yaml > anarray # load all YAML documents from 'afile.yaml'

Single objects can be written using IF::GrandeStream#putrec (aliased to IF::YAML#putobj and IF::YAML#dump)

rio('afile.yaml').yaml.putobj(anobject)

Single objects can be loaded using IF::GrandeStream#getrec (aliase to IF::YAML#getobj and IF::YAML#load)

anobject = rio('afile.yaml').yaml.getobj

A Rio in yaml-mode is just like any other Rio. And all the things you can do with any Rio come for free. They can be iterated over using IF::Grande#each and read into an array using IF::Grande#[] just like any other Rio. All the selection criteria are identical also.

Get the first three objects into an array:

array_of_objects = rio('afile.yaml').yaml[0..2]

Iterate over only YAML documents that are a kind_of ::Hash use:

rio('afile.yaml').yaml(::Hash) {|ahash| ...}

This takes advantage of the fact that the default for matching records is ===

Selecting records using a Proc can be used as normal:

anarray = rio('afile.yaml').yaml(proc{|anobject| ...}).to_a

---

See also:

• RIO::Doc::SYNOPSIS

• RIO::Doc::HOWTO

• RIO::Doc::EXAMPLES

• RIO::Rio