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Files

Reading

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

clojure

(defn read-line-by-line [fn]
(reduce str (map (partial format "%d> %s\n")
(iterate inc 1)
(read-lines fn))))

cpp C++/CLI .NET 2.0

IO::StreamReader^ stream; String^ ln; int i = 0;

try
{
stream = gcnew IO::StreamReader("test.txt");
while ((ln = stream->ReadLine())) Console::WriteLine("{0}> {1}", ++i, ln);
}

cpp C++/CLI .NET 2.0

int i = 0;
for each(String^ line in IO::File::ReadAllLines("test.txt")) Console::WriteLine("{0}> {1}", ++i, line);

csharp .Net 2.0 or later

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") }

fsharp

let stream = new StreamReader("test.txt")
let mutable i = 1
let mutable line = stream.ReadLine()
while (line <> null) do printfn "%d> %s" i line ; line <- stream.ReadLine() ; i <- i + 1 done
stream.Close()

fsharp

let proc_a_line (filename : string) proc =
let stream = new StreamReader(filename)
let rec proc_a_line' count line =
match line with
| null -> stream.Close()
| _ -> proc count line ; proc_a_line' (count + 1) (stream.ReadLine())
proc_a_line' 1 (stream.ReadLine())

// ------

let _ = proc_a_line "test.txt" (fun i line -> printfn "%d> %s" i line)

fsharp

let reader(filename : string) = seq {
use sr = new StreamReader(filename)
while not sr.EndOfStream do
let line = sr.ReadLine()
yield line
done
}

// ------

reader("test.txt") |> Seq.iteri (fun i line -> printfn "%d> %s" (i + 1) line)

fsharp

File.ReadAllLines("test.txt") |> Array.iteri (fun i line -> printfn "%d> %s" (i + 1) line)

fsharp .NET 4

// Unlike ReadAllLines, ReadLines (new in .NET 4) only reads the file
// one line at a time, rather than reading the entire file into an array first.

open System.IO
File.ReadLines("test.txt") |> Seq.iteri (fun i line -> printfn "%d> %s" (i + 1) line)

groovy

int count = 0
file.eachLine { line ->
println "${++count} > $line"
}

groovy

file.eachLine { line, count ->
println "${++count} > $line"
}

haskell

import Data.List

prefixWithNumber str n = show n ++ "> " ++ str

numberStrings (x:xs) n = prefixWithNumber x n : (numberStrings xs (n+1))
numberStrings [] n = []

main = do
str <- readFile "prefix.hs"
putStrLn (intercalate "\n" (numberStrings (lines str) 1))

haskell

prefix n str = show n ++ "> " ++ str

main = readFile "prefix.hs" >>=
putStr . unlines . zipWith prefix [1..] . lines

java

BufferedReader br = null;
try {
br = new BufferedReader(new FileReader("Solution104.java"));
String line = null;
int lineNumber = 1;
while ((line=br.readLine())!=null) {
System.out.println(lineNumber + "> " + line);
lineNumber++;
}
} catch (IOException e) {
throw new RuntimeException(e);
} finally {
if (br!=null) {
try {
br.close();
} catch (Exception e) {
// ok
}
}
}

java 1.5 or later

LineNumberReader lnr = null; PrintWriter pw = null; String line;

try
{
lnr = new LineNumberReader(new FileReader("Solution400.java"));
pw = new PrintWriter(System.out);
while ((line = lnr.readLine()) != null) pw.printf("%d> %s\n", lnr.getLineNumber(), line);
}

ocaml

let () =
let ic = open_in Sys.argv.(1) in
let i = ref 1 in
try
while true do
Printf.printf "%d> %s\n" !i (input_line ic);
incr i
done
with End_of_file ->
close_in ic

ocaml

let input_line_opt ic =
try Some (input_line ic)
with End_of_file -> None

let () =
let ic = open_in Sys.argv.(1) in
let rec aux i =
match input_line_opt ic with
| Some line ->
Printf.printf "%d> %s\n" i line;
aux (succ i)
| None ->
close_in ic
in
aux 1

perl

open(my $fh, '<', $path) or die "can't open $path: $!";
$c = 1;
print $c++ . "> $_" for (<$fh>);
close $fh;

perl

open my $fh, '<', $path or die "Can't open $path: $!";
while (<$fh>) {
print "$.> $_";
}

php

$lines = file('file.txt');
foreach ($lines as $lnum => $line) {
echo $line_num."> ".$line; // you may want to add a <br />\n
}

php PHP 5.1.0+

<?php
$lines = new SplFileObject('file.txt');
foreach ($lines as $line) {
echo $line;
}
?>

python 2.6

for no, line in enumerate(open(__file__)):
print "{0}> {1}".format(no+1, line.rstrip())

ruby

File.open("Solution103.rb").each_with_index { |line, count|
puts "#{count} > #{line}
}

scala

val source = Source.fromFile(new File("Solution468.scala")).getLines
var n = 1 ; while (source.hasNext) { printf("%d> %s", n, source.next) ; n += 1 }

scala

val source = Source.fromFile(new File("Solution469.scala")).getLines
for ((line, n) <- source zipWithIndex) { printf("%d> %s", (n + 1), line) }

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