Files and Directories

Read File

Ruby can read text from a file after another part of the program creates it.

file read `File.read` loads the whole file content as a string.

Read File

line
read_file.rb
Replay: real traced execution (multi-file project)
require "tmpdir"

line = "alpha"

Dir.mktmpdir do |dir|
  path = File.join(dir, "notes.txt")
  File.write(path, "#{line}\nsecond\n")

  content = File.read(path)
  rows = content.split("\n")

  puts "file=#{File.basename(path)}"
  puts "first=#{rows.first}"
  puts "line_count=#{rows.length}"
end

require "tmpdir"

line = "beta"

Dir.mktmpdir do |dir|
  path = File.join(dir, "notes.txt")
  File.write(path, "#{line}\nsecond\n")

  content = File.read(path)
  rows = content.split("\n")

  puts "file=#{File.basename(path)}"
  puts "first=#{rows.first}"
  puts "line_count=#{rows.length}"
end

require "tmpdir"

line = "gamma"

Dir.mktmpdir do |dir|
  path = File.join(dir, "notes.txt")
  File.write(path, "#{line}\nsecond\n")

  content = File.read(path)
  rows = content.split("\n")

  puts "file=#{File.basename(path)}"
  puts "first=#{rows.first}"
  puts "line_count=#{rows.length}"
end

  1. line ← alpha

    1require "tmpdir"23line→ alpha = "alpha"  #@line="beta", "gamma"45Dir.mktmpdir do |dir|6  path = File.join(dir, "notes.txt")7  File.write(path, "#{line}\nsecond\n")89  content = File.read(path)10  rows = content.split("\n")1112  puts "file=#{File.basename(path)}"13  puts "first=#{rows.first}"14  puts "line_count=#{rows.length}"15end

  2. path ← /tmp/⟨tmp A⟩/notes.txt, content ← alpha\nsecond\n, rows ← ["alpha", "second"]

    5Dir.mktmpdir do |dir/tmp/⟨tmp A⟩|6  path→ /tmp/⟨tmp A⟩/notes.txt = File.join(dir, "notes.txt")/tmp/⟨tmp A⟩/notes.txt7  File.write(path/tmp/⟨tmp A⟩/notes.txt, "#{linealpha}\nsecond\n")89  content→ alpha\nsecond\n = File.read(path)alpha\nsecond\n10  rows→ ["alpha", "second"] = content.split("\n")["alpha", "second"]1112  puts "file=#{File.basename(path)notes.txt}"13  puts "first=#{rows.firstalpha}"14  puts "line_count=#{rows.length2}"15end
    outputfile=notes.txt
first=alpha
line_count=2

  1. line ← beta

    1require "tmpdir"23line→ beta = "beta"45Dir.mktmpdir do |dir|6  path = File.join(dir, "notes.txt")7  File.write(path, "#{line}\nsecond\n")89  content = File.read(path)10  rows = content.split("\n")1112  puts "file=#{File.basename(path)}"13  puts "first=#{rows.first}"14  puts "line_count=#{rows.length}"15end

  2. path ← /tmp/⟨tmp A⟩/notes.txt, content ← beta\nsecond\n, rows ← ["beta", "second"]

    5Dir.mktmpdir do |dir/tmp/⟨tmp A⟩|6  path→ /tmp/⟨tmp A⟩/notes.txt = File.join(dir, "notes.txt")/tmp/⟨tmp A⟩/notes.txt7  File.write(path/tmp/⟨tmp A⟩/notes.txt, "#{linebeta}\nsecond\n")89  content→ beta\nsecond\n = File.read(path)beta\nsecond\n10  rows→ ["beta", "second"] = content.split("\n")["beta", "second"]1112  puts "file=#{File.basename(path)notes.txt}"13  puts "first=#{rows.firstbeta}"14  puts "line_count=#{rows.length2}"15end
    outputfile=notes.txt
first=beta
line_count=2

  1. line ← gamma

    1require "tmpdir"23line→ gamma = "gamma"45Dir.mktmpdir do |dir|6  path = File.join(dir, "notes.txt")7  File.write(path, "#{line}\nsecond\n")89  content = File.read(path)10  rows = content.split("\n")1112  puts "file=#{File.basename(path)}"13  puts "first=#{rows.first}"14  puts "line_count=#{rows.length}"15end

  2. path ← /tmp/⟨tmp A⟩/notes.txt, content ← gamma\nsecond\n, rows ← ["gamma", "second"]

    5Dir.mktmpdir do |dir/tmp/⟨tmp A⟩|6  path→ /tmp/⟨tmp A⟩/notes.txt = File.join(dir, "notes.txt")/tmp/⟨tmp A⟩/notes.txt7  File.write(path/tmp/⟨tmp A⟩/notes.txt, "#{linegamma}\nsecond\n")89  content→ gamma\nsecond\n = File.read(path)gamma\nsecond\n10  rows→ ["gamma", "second"] = content.split("\n")["gamma", "second"]1112  puts "file=#{File.basename(path)notes.txt}"13  puts "first=#{rows.firstgamma}"14  puts "line_count=#{rows.length2}"15end
    outputfile=notes.txt
first=gamma
line_count=2