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scanf is an implementation of the C function scanf(3), modified as necessary for Ruby compatibility.

The methods provided are String#scanf, IO#scanf, and Kernel#scanf. Kernel#scanf is a wrapper around STDIN.scanf. IO#scanf can be used on any IO stream, including file handles and sockets. scanf can be called either with or without a block.

Scanf scans an input string or stream according to a format, as described below in Conversions, and returns an array of matches between the format and the input. The format is defined in a string, and is similar (though not identical) to the formats used in Kernel#printf and Kernel#sprintf.

The format may contain conversion specifiers, which tell scanf what form (type) each particular matched substring should be converted to (e.g., decimal integer, floating point number, literal string, etc.) The matches and conversions take place from left to right, and the conversions themselves are returned as an array.

The format string may also contain characters other than those in the conversion specifiers. Whitespace (blanks, tabs, or newlines) in the format string matches any amount of whitespace, including none, in the input. Everything else matches only itself.

Scanning stops, and scanf returns, when any input character fails to match the specifications in the format string, or when input is exhausted, or when everything in the format string has been matched. All matches found up to the stopping point are returned in the return array (or yielded to the block, if a block was given).


Add this line to your application's Gemfile:

gem 'scanf'

And then execute:

$ bundle

Or install it yourself as:

$ gem install scanf


require 'scanf'

# String#scanf and IO#scanf take a single argument, the format string
array = a_string.scanf("%d%s")
array = an_io.scanf("%d%s")

# Kernel#scanf reads from STDIN
array = scanf("%d%s")


After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the 2-Clause BSD License.