{"id":40839,"date":"2026-01-06T14:24:44","date_gmt":"2026-01-06T14:24:44","guid":{"rendered":"https:\/\/www.railscarma.com\/?p=40839"},"modified":"2026-01-06T14:24:47","modified_gmt":"2026-01-06T14:24:47","slug":"how-to-read-and-write-files-in-ruby-with-examples","status":"publish","type":"post","link":"https:\/\/www.railscarma.com\/sv\/blogg\/how-to-read-and-write-files-in-ruby-with-examples\/","title":{"rendered":"How To Read and Write Files in Ruby (With Examples)"},"content":{"rendered":"
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Ruby provides simple, elegant, and powerful ways to read from and write to files. The language emphasizes readability and developer happiness, making file I\/O operations straightforward. This guide covers the most common and idiomatic approaches with practical examples.<\/p>

Basic Concepts<\/strong><\/h3>

In Ruby, file operations are typically performed using the File<\/code> class or the shorter File.open<\/code> method. Most file operations use block<\/strong> to ensure files are properly closed after use, preventing resource leaks.<\/p>

Opening a File<\/strong><\/h3>

The recommended way is to use a block form:<\/p>

ruby\nFile.open(\"filename.txt\", \"r\") do |file|\n  # work with the file<\/em>\nslutet\n# file is automatically closed here<\/em><\/pre>
Without a block, you must manually close the file:<\/p>
ruby\nfile = File.open(\"filename.txt\", \"r\")\n# ... operations ...<\/em>\nfile.close<\/pre>
File Modes<\/strong><\/h3>
The second argument to File.open<\/code> is the mode<\/strong> string:<\/p>
Mode<\/strong><\/td>Meaning<\/strong><\/td><\/tr>
“r”<\/td>Read-only (default)<\/td><\/tr>
“w”<\/td>Write-only, creates\/truncates file<\/td><\/tr>
“a”<\/td>Write-only, appends to file<\/td><\/tr>
“r+”<\/td>Read and write, preserves content<\/td><\/tr>
“w+”<\/td>Read and write, truncates file<\/td><\/tr>
“a+”<\/td>Read and write, appends<\/td><\/tr><\/tbody><\/table>
Add “b” for binary mode on Windows (e.g., “rb”, “wb”).<\/p>
Reading Files in Ruby<\/strong><\/h3>
1. Read Entire File as a String<\/strong><\/p>
ruby\ncontent = File.read(\"example.txt\")\nputs content<\/pre>
Or using File.open<\/code>:<\/p>
ruby\ncontent = File.open(\"example.txt\", \"r\") { |f| f.read }<\/pre>
2. Read Entire File into an Array of Lines<\/strong><\/p>
ruby\nlines = File.readlines(\"example.txt\")\nlines.each { |line| puts line }\n\n# Or more idiomatically:<\/em>\nFile.readlines(\"example.txt\").each do |line|\n  puts \"Line: #{line.chomp}\"\nend<\/pre>
3.<\/strong> Read Line by Line (Most Memory-Efficient)<\/strong><\/p>
Ideal for large files:<\/p>
ruby\nFile.open(\"large_file.txt\", \"r\") do |file|\n  file.each_line do |line|\n \u00a0\u00a0 puts line.chomp.upcase\n  end\nend<\/pre>
Or using the shorter foreach<\/code>:<\/p>
ruby\nFile.foreach(\"large_file.txt\") do |line|\n  process(line.chomp)\nend<\/pre>
4. Read Specific Number of Bytes or Lines<\/strong><\/p>
ruby\nFile.open(\"data.bin\", \"rb\") do |f|\n  header = f.read(16)\u00a0\u00a0\u00a0\u00a0\u00a0 # read first 16 bytes<\/em>\n  puts header\nend\n\n# Read first 5 lines<\/em>\nfirst_five = File.foreach(\"log.txt\").first(5)<\/pre>
5. Read with Encoding Specified<\/strong><\/p>
ruby\ncontent = File.read(\"utf8_file.txt\", encoding: \"UTF-8\")\n# or<\/em>\nFile.open(\"file.txt\", \"r:UTF-8\") do |f|\n  f.each_line { |line| puts line }\nend<\/pre>
Writing Files in Ruby<\/strong><\/h3>
1. Write a String to a File (Overwrites)<\/strong><\/p>
ruby\nFile.write(\"output.txt\", \"Hello, Ruby!\\nThis is a new file.\")<\/pre>
This is the simplest and most common way.<\/p>
2. Write Using File.open (Block Form)<\/strong><\/p>
ruby\nFile.open(\"greeting.txt\", \"w\") do |file|\n  file.puts \"Hello World\"\n  file.puts \"Welcome to Ruby file I\/O\"\n  file.write \"This line is written without newline\"\n  file << \" << This uses the shovel operator\\n\"\nend<\/pre>
Methods available inside the block:<\/p>