View Category
Files
Reading

Read the contents of a file into a string

ruby
file = File.new("Solution108.rb")
whole_file = file.read
csharp
string contents = System.IO.File.ReadAllText("filename.txt");
fantom
contents := File(`file.text`).readAllStr
erlang
Text = readfile("Solution607.erl"),
Text = readfile("Solution608.erl"),

Process a file one line at a time

Open the source file to your solution and print each line in the file, prefixed by the line number, like:
1> First line of file
2> Second line of file
3> Third line of file
ruby
File.open("Solution103.rb").each_with_index { |line, count|
puts "#{count} > #{line}
}
csharp
int counter = 0;

// If the file is large, you would want to buffer this instead of reading everything at once
foreach (string line in System.IO.File.ReadAllLines("filename.txt"))
{
Console.WriteLine("{0}> {1}", ++counter, line);
}
fantom
File(`input.text`).readAllLines.each |Str s, Int i| { echo("${i+1}> $s") }
erlang
Reader = fun (IODevice) -> io:get_line(IODevice, "") end,
Worker = fun (Line, N) -> io:format("~B> ~s", [N, Line]), N + 1 end,

while_not_eof("Solution609.erl", Reader, Worker, 1).
Reader = fun (Filename) -> {ok, Contents} = file:read_file(Filename), Contents end,
Transformer = fun (Line, N) -> string:concat(string:concat(integer_to_list(N), "> "), Line) end,
Printer = fun (Line) -> io:format("~s~n", [Line]) end,

Lines = string:tokens(binary_to_list(Reader("Solution610.erl")), "\n"),
NewLines = lists:zipwith(Transformer, Lines, lists:seq(1, length(Lines))),
lists:foreach(Printer, NewLines).
Writing

Write a string to a file

ruby
File.new("a_file", "w") << "some text"
csharp
System.IO.File.WriteAllText("filename.txt", "Some text to write to the file");
fantom
File(`out.txt`).out.writeChars("some text").flush
erlang
Line = "This line overwites file contents!\n",
{ok, IODevice} = file:open("test.txt", [write]), file:write(IODevice, Line), file:close(IODevice).

Append to a file

ruby
file = File.new('/tmp/test.txt', 'a+') ; file.puts 'This line appended to file!!' ; file.close()
csharp
System.IO.File.AppendAllText("filename.txt", "Some text to append to the file");
fantom
File(`out.txt`).out(true).writeChars("some text").flush
erlang
Line = "This line appended to file!\n",
{ok, IODevice} = file:open("test.txt", [append]), file:write(IODevice, Line), file:close(IODevice).
Directories

Process each file in a directory

ruby
directory = '/tmp' ; Dir.foreach(directory) {|file| puts "#{file}"}
csharp
foreach (string filename in System.IO.Directory.GetFiles(directory)) ProcessFile(filename);
fantom
File(`./`).list.each { process(it) }
erlang
% File basenames only - many tasks require absolute paths to work
lists:foreach(fun (FileOrDirPath) -> Worker(FileOrDirPath) end, file:list_dir(Directory)).
% Absolute paths provided - will accomodate most tasks
lists:foreach(fun (FileOrDirPath) -> Worker(FileOrDirPath) end, list_dir_path(Directory)).

Process each file in a directory recursively

ruby
def procdir(dirname)
Dir.foreach(dirname) do |dir|
dirpath = dirname + '/' + dir
if File.directory?(dirpath) then
if dir != '.' && dir != '..' then
puts "DIRECTORY: #{dirpath}" ; procdir(dirpath)
end
else
puts "FILE: #{dirpath}"
end
end
end

# ------

procdir('/tmp')
fantom
File(`./`).walk { process(it) }
erlang
filelib:fold_files(Directory, ".*", true, fun (FileOrDirPath, Acc) -> Worker(FileOrDirPath), Acc end, []).
process_dir(Directory, Worker).