在Windows命令行上，如何将cat的输出输入到java main方法中？

Question

I can't figure out how to get the command line command "cat" and my trivial Java program to work together in a Windows command line. In the same way that it's common in Linux to use:

cat *.* | grep stackoverflow

I would like to do this in Windows:

cat inputfile.txt | java Boil

I can't get cat to feed Boil though. As you can see below, the command line command "cat" works fine, and the Boil program works fine if I supply it with parameters in the format "java Boil these are parameters".

My Boil.java code

// Boil down lines of input code to just ;{}( and )
//          and enjoy seeing the patterns
public class Boil {
    public static void main(String[] args) {
        int outputCounter = 0;
        for (int i = 0; i < args.length; i++) {
            for (int j = 0; j < args[i].length(); j++) {
                if (args[i].charAt(j) == ';' 
                        || args[i].charAt(j) == '(' 
                        || args[i].charAt(j) == ')' 
                        || args[i].charAt(j) == '{' 
                        || args[i].charAt(j) == '}') {
                    System.out.print(args[i].charAt(j));
                    outputCounter++;
                    if (outputCounter >= 80) {
                        System.out.print("\n");
                        outputCounter = 0;
                    }
                }   
            }
        }
    }
}    

I know this could be better optimized :)

From my C:\\Windows\\System32\\cmd.exe, 'Administrator: cmd.exe' Windows command line window, running on a computer with Windows 7 Professional SP1 32 bit OS:

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Windows\System32>cd ../../workspace1/Boil/bin

C:\workspace1\Boil\bin>ls
Boil.class     inputfile.txt

C:\workspace1\Boil\bin>cat inputfile.txt
This is a sample text file() with {
        multiple lines!;
}
C:\workspace1\Boil\bin>java Boil this should print nothing

C:\workspace1\Boil\bin>java Boil this should print a semicolon; ok?
;
C:\workspace1\Boil\bin>java Boil test all good chars ;(){}
;(){}
C:\workspace1\Boil\bin>cat inputfile.txt | java Boil

C:\workspace1\Boil\bin>java Boil < inputfile.txt

C:\workspace1\Boil\bin>java Boil < cat inputfile.txt
The system cannot find the file specified.

C:\workspace1\Boil\bin>cat inputfile.txt > java Boil
cat: Boil: No such file or directory

C:\workspace1\Boil\bin>dir
 Volume in drive C is OS
 Volume Serial Number is 0666-2986

 Directory of C:\workspace1\Boil\bin

11/20/2013  04:29 PM    <DIR>          .
11/20/2013  04:29 PM    <DIR>          ..
11/20/2013  02:28 PM               864 Boil.class
11/20/2013  04:22 PM                57 inputfile.txt
11/20/2013  04:29 PM                57 java
               3 File(s)            978 bytes
               2 Dir(s)  872,764,809,216 bytes free

C:\workspace1\Boil\bin>cat java
This is a sample text file() with {
        multiple lines!;
}
C:\workspace1\Boil\bin>rm java

Any thoughts much appreciated. Thank you in advance.

Answer 1

Instead of trying to read the lines as arguments, you should be reading from the standard input stream.

try {
    BufferedReader br = 
                  new BufferedReader(new InputStreamReader(System.in));

    String input;

    while((input = br.readLine()) != null){
        System.out.println(input);
    }

} catch (IOException io){
    io.printStackTrace();
}   

Piping means passing the output stream (STDOUT) to another command as STDIN. In this example, Boil nor grep get any arguments.

Answer 2

If your command is java Boil , there are no arguments. Therefore, none of the code in your loop will ever execute. You're trying to get the cat command to feed its output into the arguments of the command, but you can't do that in Windows. (Using | doesn't do that on Unix/Linux, either. You have to use backticks to accomplish that. But Windows doesn't support backticks.)

(PS The command you gave on Linux:

cat *.* | grep stackoverflow

doesn't do what you seem to think it does. After the pattern, " stackoverflow ", grep expects to see file names of files to search, or if there aren't any, it uses standard input. | pipes the output of cat to grep 's standard input, not to the command-line arguments. You couldn't use this to use the output of cat as the pattern for grep [unless there's some way to use the -f option for this].)