How to write to a file in Ruby
File handling is an essential aspect of programming that allows you to read from and write data to files. In Ruby, the File class provides a set of methods that make file manipulation straightforward and efficient.
Whether you're working with text files, binary files, or any other type of file, you'll want to know how to create, read, and write files in Ruby.
Creating a file in Ruby is a simple process that involves using the File class and some of its associated methods. Let's start with the basics.
File.new
The File.new method is one of the primary ways to create a file in Ruby. Here are two examples of how to use it:Two examples using File.new
file_name = File.new("example.txt", "w")
# use the w flag as shown above if
# you want to write to a new file
file_name.close
file_name = File.new("example.txt", "a")
# use the w flag as shown above if
# you want to append to a pre-existing file
file_name.close
In the first code example above, the File.new method creates a new file called example.txt in write mode ("w.") It can also take an old file called example.txt, remove the content, and overwrite it with the "a" flag. The File.close method ensures that the file is properly closed after it's created or overwritten.
This is a simple and easy-to-understand method that is useful for a quick one-off file creation.
Comparison of File Handling Methods in Ruby
Method | Overwrite / Append | When to use | Drawbacks |
|---|---|---|---|
File.new | Both | Basic file creation, manual handling | Must manually manage file |
File.open | Both | Flexible file handling with block support | None |
File.write | Overwrites by default, but can append with a flag | Quick file writing | Less control over file handling as compared to File.open |
FileUtils.touch | Neither | Creating an empty file or updating timestamps | Does not allow for file manipulation |
IO.sysopen + IO.sysnew | Both | offers low-level file operations for more control | Complex |
Tempfile | Overwrites | Creating files for temporary use | Not suitable for long-term storage |
Pathname + open | Both | Object-oriented file handling | Requires setup with the Pathname library |
File.open
Another common method for creating files in Ruby is File.open. This method is similar to File.new but uses a block syntax that can make it easier to manage any other operations you want to do on the file.Example of File.open
File.open("example.txt", "w") do |file|
#Other operations go here
end
In the example above, the File.open method creates the example.txt file in write mode, and then it goes to the block for any further operations you want to do on the file. When the block ends, the file closes automatically.
The behavior of File.open is similar to File.new in that a "w" flag will overwrite or create a new file, and "a" will append.
While the previous method is more succinct, you'll likely more often find yourself using this technique as the code block allows you more functionality in your code. This is my go-to method for creating files in Ruby.
In the example above, the File.open method creates the example.txt file in write mode, and then it goes to the block for any further operations you want to do on the file. When the block ends, the file closes automatically.
The behavior of File.open is similar to File.new in that a "w" flag will overwrite or create a new file, and "a" will append.
While the previous method is more succinct, you'll likely more often find yourself using this technique as the code block allows you more functionality in your code. This is my go-to method for creating files in Ruby.
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File.write
This is not my favorite file creation method in Ruby, nor is it intuitive. However, it is succinct, which does have its own benefits, and it's important to include this for completion. Here's how to create a file with File.write:Example of File.write
File.write('example.txt', 'really cool text here')
Example of File.write with append
File.write('example.txt', "Text to append.\n", mode: 'a')
# append mode must be explicitly specified
# append mode must be explicitly specified
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Close your files! One common pitfall that people run into when creating files in Ruby is forgetting to close a file after they're done with it. Using block syntax can help prevent this.
FileUtils.touch
If you're familiar with Unix, you'll immediately recognize this. The FileUtils module has a method called touch. Touch is primarily used to update a file's access and modify timestamps or, as in our case, it can be used to create a file if it doesn't exist. This method is particularly useful if you want to create an empty file without opening it for reading or writing.Example of FileUtils.touch
require 'fileutils'
FileUtils.touch('example.txt')
IO.sysopen and IO.sysnew
If you're used to writing in low-level programming languages or just want more control over file descriptors, using IO.sysopen in conjunction with IO.sysnew is a good option.This method is also slightly useful for obfuscation. I appreciate this as using low-level methodologies on a high-level language for the sole reason of being confusing is peak absurdity.
Example of IO.sysopen and IO.sysnew
fd = IO.sysopen("example.txt", "w")
# you can elect to use append flag "a"
file = IO.new(fd, "w")
file.puts "some low-level file operation"
file.close
Tempfile
If you're wanting to create a tempfile, Ruby has a built-in tempfile class that will help you get this done. These are great for immediate use and are automatically deleted when no longer needed. Let's see it in action!Example of Tempfile
require 'tempfile'
tempfile = Tempfile.new('example')
tempfile.puts "This is an awesome yet fleeting moment"
tempfile.close
Pathname and open
If you're a fan of object-oriented programming (and you should be, because you're programming in Ruby in the first place) then you might like this method for creating files in Ruby. Let's get to the guts of the code.Example of Pathname and open
require 'pathname'
path = Pathname.new("example.txt")
path.open("w") do |file|
file.puts "I made this rad file using Pathname"
end
path.open("w") do |file|
file.puts "I made this rad file using Pathname"
end
File Modes
File Mode | What it does |
|---|---|
"r" | This is read-only mode. It will open the file for reading. |
"w" | This is write mode. It will create a new file or truncate an existing file for writing. |
"a" | This is append mode. This will open the file for writing and append data to the end. |
"r+" | This is read-write mode. It'll open a file for both reading and writing. |
"w+" | This is write-read mode. It will create a new file or truncate an existing file for reading and writing. |
"a+" | This is append-read mode. This will open the file for reading and writing and append data to the end. |
- FileUtils.touch will create empty files without opening them.
- IO.sysopen and IO.new will allow you to do low-level file operations.
- Tempfile is a good way to create temporary files.
- Pathname gives you an object-oriented approach.
References
Lucas Carlson and Leonard Richardson, Ruby Cookbook, 2nd ed. (Sebastopol, CA: O'Reilly Media, 2015), 228.Dave Thomas, Programming Ruby 3.3: The Pragmatic Programmers' Guide, 5th ed. (The Pragmatic Bookshelf, [2024]).
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