File I/O

## Learning Objectives - Read from and write to files - Work with file paths and directories - Use File class methods - Handle file-related exceptions ## File Reading ### Read Entire File ```ruby content = File.read("example.txt") puts content ``` ### Read Line by Line ```ruby File.open("example.txt", "r") do |file| file.each_line do |line| puts line end end # Or with block shorthand File.foreach("example.txt") { |line| puts line } ``` ### Read with Encoding ```ruby content = File.read("example.txt", encoding: "UTF-8") content = File.read("example.txt", encoding: "Windows-1252") ``` ## File Writing ### Write to File ```ruby File.write("output.txt", "Hello, World!") # Append mode File.write("output.txt", "More content\n", mode: "a") ``` ### Open and Write ```ruby File.open("output.txt", "w") do |file| file.puts "Line 1" file.puts "Line 2" file.write "No newline" end ``` ## File Modes | Mode | Description | |------|-------------| | `r` | Read only (default) | | `w` | Write only (truncates) | | `a` | Append | | `r+` | Read and write | | `w+` | Read and write (truncates) | | `a+` | Read and append | ## File Operations ### Check File Existence ```ruby File.exist?("example.txt") File.file?("example.txt") File.directory?("path") ``` ### File Info ```ruby File.size("example.txt") File.mtime("example.txt") # Modification time File.atime("example.txt") # Access time File.extname("file.txt") # ".txt" File.basename("/path/file.txt") # "file.txt" File.dirname("/path/file.txt") # "/path" ``` ### Copy, Move, Delete ```ruby FileUtils.cp("source.txt", "dest.txt") FileUtils.mv("old.txt", "new.txt") FileUtils.rm("file.txt") # Or built-in File.copy("source.txt", "dest.txt") File.delete("file.txt") ``` ## Directories ### Reading Directory Contents ```ruby Dir.foreach(".") do |entry| puts entry unless entry.start_with?(".") end # Glob pattern Dir.glob("*.rb") # All Ruby files Dir.glob("**/*.rb") # Recursive Dir.glob("{app,config}/*.rb") # Multiple patterns ``` ### Create and Delete Directories ```ruby Dir.mkdir("new_directory") Dir.rmdir("empty_directory") # Recursive create require 'fileutils' FileUtils.mkdir_p("a/b/c/d") ``` ### Change Directory ```ruby Dir.chdir("/tmp") puts Dir.pwd # Current directory ``` ## Pathname ```ruby require 'pathname' path = Pathname.new("/home/user/docs/report.pdf") path.basename # "report.pdf" path.dirname # "/home/user/docs" path.extname # ".pdf" path.parent # "/home/user/docs" path.join("..", "backup", "report.pdf") path.exist? path.directory? path.file? ``` ## Working with CSV ```ruby require 'csv' # Reading CSV.foreach("data.csv") do |row| puts row.join(", ") end # Writing CSV.open("output.csv", "w") do |csv| csv << ["Name", "Age"] csv << ["Alice", 30] csv << ["Bob", 25] end # To array csv_data = CSV.read("data.csv") ``` ## Working with JSON ```ruby require 'json' # Read JSON json_string = File.read("data.json") data = JSON.parse(json_string) # Write JSON data = { name: "Alice", age: 30 } File.write("data.json", JSON.generate(data)) # Pretty print File.write("data.json", JSON.pretty_generate(data)) ``` ## Working with YAML ```ruby require 'yaml' # Read YAML data = YAML.load_file("config.yml") # Write YAML File.write("config.yml", YAML.dump(data)) ``` ## Tempfile ```ruby require 'tempfile' file = Tempfile.new("myapp") file.write("Temporary data") file.rewind puts file.read file.close file.unlink # Delete # Block form - auto cleans up Tempfile.create("myapp") do |f| f.write("Temporary data") puts f.read end ``` ## File Locking ```ruby File.open("shared.txt", "w") do |f| f.flock(File::LOCK_EX) # Exclusive lock f.write("Data") f.flock(File::LOCK_UN) # Unlock end # Shared lock for reading File.open("shared.txt", "r") do |f| f.flock(File::LOCK_SH) # Shared lock puts f.read end ``` ## Binary Files ```ruby # Read binary File.binread("image.png") # Write binary File.binwrite("copy.png", File.binread("original.png")) # With mode File.open("image.png", "rb") do |f| data = f.read end ``` ## Error Handling with Files ```ruby begin File.open("example.txt", "r") do |file| content = file.read end rescue Errno::ENOENT puts "File not found" rescue Errno::EACCES puts "Permission denied" rescue => e puts "Error: #{e.message}" end ``` ## Summary - `File.read`/`File.write` for simple operations - `File.open` with block ensures proper closing - File modes: `r`, `w`, `a`, `r+`, `w+`, `a+` - `Dir` class for directory operations - `Pathname` for path manipulation - `CSV`, `JSON`, `YAML` libraries for structured data - `Tempfile` for temporary files - `FileUtils` for common file operations - Handle `Errno::ENOENT` for missing files