Question

I am writing a program that takes one action if the command line contains a stream redirection, such as > or <, but takes another action otherwise.

My first instinct was to loop through the command line and check if each argument equals the redirection symbol, like this:

public boolean hasRedirection(String[] args){
    boolean flag = false;
    int length = args.length;
    int i;
    for(i = 0; i < length; i++){
        System.out.println(args[i]);
        if(args[i].equals(">") || args[i].equals("<"))
            flag = true;
    }
    return flag;
}

However, it always returns false. The line System.out.println(args[i]); shows that any redirection and subsequent filename are not being recognized. For example:

project\src>java myProgram.Client localhost 1234 > myFile.txt
localhost
1234

whereas it should be:

project\src>java myProgram.Client localhost 1234 > myFile.txt
localhost
1234
>
myFile.txt

Is there a simpler way I can do this? Thanks for your time!

Answer 1

The redirection is part of the shell’s syntax, not something passed along to the program. Instead, check whether System.console() returns a non-null value.