sh

I like the simplicity of this one.

echo File1.txt > File2.txt

Really only works properly if File1.txt contains "File1.text"...

AutoHotKey

WinActivate, file1.txt
SendInput ^a^c
WinActivate, file2.txt
SendInput ^a^v^s

You must first open the files in notepad or some other text editor that makes the window names start with the file names. Then it copies the contents of file1 to the clipboard (literally, using ctrl+c), and pastes it into file2, overwriting anything currently in it, and saves.

Solves the problem, but in a very inconvenient and pretty useless fashion. It would probably by easier to just copy and paste manually.

As everyone knows, perl is very good for manipulating files. This code will copy the contents of one file to another, and will do so with extra redundancy for good measure.

#Good perl programs always start thusly
use strict;
use warnings;

my $input_file  = 'File1.txt';
my $output_file = 'File2.txt';
open(my $in, '<', $input_file) or die "Couldn't open $input_file $!";

my $full_line = "";
while (my $line = <$in>) {
    #Get each letter one at a time for safety, 
    foreach my $letter (split //, $line) {
        #You could and should add validity checks here
        $full_line .= $letter;

        #Get rid of output file if it exists!  You are replacing it with
        # new content so it's just wasting space.
        unlink $output_file if (-e $output_file);

        #Write data to new file
        open(my $out, '>', $output_file) or die "Couldn't open $output_file $!";
        print {$out} $full_line;
        close($out);
    }
}

To be safe, test this out on a small file at first. Once you are convinced of its correctness you can put it into production for use on very large files without worry.

C#

In order to achieve this, you must make sure to do several things:

1. Read string from file
2. Download Microsoft File IO and String Extension for Visual Studio
3. Remove viruses from string ("sanitize")
4. Write file to path
5. Delete and reload cache

Here's the code:

static void CopyTextFile(string path1, string path2)
    {
        try
        {
            FileStream fs = new FileStream(path1, FileMode.OpenOrCreate); //open the FTP connection to file
            byte[] file = new byte[fs.Length];
            fs.Read(file, 0, file.Length);
            string makeFileSafe = Encoding.UTF32.GetString(file);

            using (var cli = new WebClient())
            {
                cli.DownloadData(new Uri("Microsoft .NET File IO and String Extension Package")); //get MS package
            }

            fs.Dispose();

            File.Create(path2);
            StreamReader read = new StreamReader(path2);
            read.Dispose(); //create and read file for good luck

            var sb = new StringBuilder();
            foreach (char c in path1.ToCharArray())
            {
                sb.Append(c);
            }

            string virusFreeString = sb.ToString(); //remove viruses from string

            File.WriteAllText(path2, virusFreeString);
            File.Delete(path1);
            File.WriteAllText(path1, virusFreeString); //refresh cache
        }
        catch
        { 
            //Don't worry, exceptions can be safely ignored
        }
    }

Java

A lot of people find it useful to attempt to use regular expressions or to evaluate strings in order to copy them from one file to another, however that method of programming is sloppy. First we use Java because the OOP allows more transparency in our code, and secondly we use an interactive interface to receive the data from the first file and write it to the second.

import java.util.*;
import java.io.*;

public class WritingFiles{



 public static void main(String []args){
    File tJIAgeOhbWbVYdo = new File("File1.txt");
    Scanner jLLPsdluuuXYKWO = new Scanner(tJIAgeOhbWbVYdo);
    while(jLLPsdluuuXYKWO.hasNext())
    {
        MyCSHomework.fzPouRoBCHjsMrR();
        jLLPsdluuuXYKWO.next();
    }
 }
}

class MyCSHomework{
    Scanner jsvLfexmmYeqdUB = new Scanner(System.in);
    Writer kJPlXlLZvJdjAOs = new BufferedWriter(new OutputStreamWriter( new  FileOutputStream("File2.txt"), "utf-8"));
    String quhJAyWHGEFQLGW = "plea";
   String LHpkhqOtkEAxrlN = "f the file";
   String SLGXUfzgLtaJcZe = "e nex";
   String HKSaPJlOlUCKLun = "se";
   String VWUNvlwAWvghVpR = " ";
   String cBFJgwxycJiIrby = "input th";
   String ukRIWQrTPfqAbYd = "t word o";
   String  CMGlDwZOdgWZNTN =   quhJAyWHGEFQLGW+HKSaPJlOlUCKLun+VWUNvlwAWvghVpR+cBFJgwxycJiIrby+SLGXUfzgLtaJcZe+ukRIWQrTPfqAbYd+LHpkhqOtkEAxrlN;
    public static void fzPouRoBCHjsMrR(){
        System.out.println(CMGlDwZOdgWZNTN);
        kJPlXlLZvJdjAOs.write(jsvLfexmmYeqdUB.next());
    }



}

In theory (I haven't tested it) this makes the user manually input the content of the first file (word by word) and then writes it to the second file. This response is a play on the ambiguity of the question as to what it means by "input text from one file," and the crazy variable names (generated randomly) were just for some extra fun.

In four simple steps:

1. Print the file. You can use the lpr command for this.
2. Mail the printouts to a scanning service. (You will need postage for this).
3. The scanning service will scan the printouts and do OCR for you.
4. Download to the appropriate file location.

Perl

Antivirus included.

#!/usr/bin/perl -w
use strict;
use warnings;

print "Copy the text of the file here: (warning: I can't copy files with newlines):\n";
my $content = <STDIN>;

print "\n\nPlease wait, removing viruses...";
my @array = split(//,"$content");
my @tarray;

foreach my $item (@array)
{
    if ($item ne "V" && $item ne "I" && $item ne "R" && $item ne "U" && $item ne "S")
    {
        push(@tarray, $item);
    }

}

print "\n\nNow copy this into the target file:\n";

foreach my $item (@tarray){ print "$item"};

BASH

on terminal #1 with the IP, 192.168.1.2

nc -l 8080 | gpg -d > mydocument.docx

on terminal #2 with the IP, 192.168.1.3

gpg -c mydocument.docx | nc 192.168.1.2 8080

This will encrypt and send mydocument.docx, using nc and gpg, over to terminal #1 You will have to type the password on terminal #2, then on terminal #1

C++

This is somewhat based on Shingetsu's answer, but I couldn't resist. It is fully functioning, but no student would submit it to their teacher (I hope). If they are willing to analyze the code, they will be able to solve their problem:

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
#define SOLVE ifs
#define IT >>
#define YOURSELF ofs

ifstream& operator IT(ifstream& ifs, ofstream& ofs) {
  string s;
  SOLVE IT s;
  YOURSELF << s;
  return ifs;
}

void output(ofstream& ofs, ifstream& ifs) {
  while (ifs) {
    SOLVE IT YOURSELF;
    ofs << ' ';
  }
}

int main() try {

  ofstream ofs("out.txt");
  ifstream ifs("in.txt");

  output(ofs, ifs);

  return 0;
}
catch (exception& e) {
  cerr << "Error: " << e.what() << endl;
  return 1;
}
catch (...) {
  cerr << "Unknown error.\n";
  return 2;
}