how to check stdin for piped data

[HowardL]

Hi,
I would like to be able to either pipe data into my prog from stdin or get data from a file.
If I try to check by using

 if( Console.In.Peek() != -1 )
    {
      Console.WriteLine("GOT STDIN");
      return;
    } 

...it blocks and user must hit return to continue.
Is there a test I can do in C# that will not block?
Thanks

[tlhintoq]

If it were a WinForm app I would suggest reacting to the keypress event.
That way as soon as any key is pressed you can move on to whatever you like.
Does it have to be a console app?

[Plater]

Does this work?
Console.OpenStandardInput().Length

[HowardL]

Thanks for your replies.
> Does it have to be a console app? - reacting to the keypress event
Yes it is just a filter app.

I think you CAN get keypress events in a Console app but
I don't think piped data would cause a keypress event and
the program will not be taking any Q&A user input.
The program will filter a stream of floating point numbers.
I wanted the user to be able to supply the stream either:
- piped in on the command line
. . eg: echo "1.2334 2.345 3.456 " | myprog
- or from a file supplied by user as arg[0]

If neither is supplied the prog will create it's own sample data.

I couldnt get anything out of "Console.OpenStandardInput().Length"

    //Console.WriteLine("Console.OpenStandardInput().Length= {0}", 
    //                                   Console.OpenStandardInput().Length );
    // exception: The stream does not support seeking (with or without piped data)
 

Here is an example of my novice level and the things I have tried:

using System;
using System.Text; // for ReadKey()
using System.IO;   // for StreamReader etc
 
class MyProg
{
  static void Main(string[] args)
  {
    //string s1;
    //int i;
    char c;
 
    Console.WriteLine("-----test-----");
 
/****  So far everything has blocked the same as Console.Read():         ****/
    while( Console.In.Peek() != -1 ) // blocks at first read... 
    {
      //s1 = Console.ReadLine();
      //Console.Write(s1);
 
      //i = Console.Read();
      //Console.Write("{0} ", i);
 
      c = (char)Console.Read();
      Console.Write("{0} ", c);
 
      //c = Console.ReadKey();   // even with:  using System.Text; still gets:
      //     Error: System.Console' does not contain a definition for `ReadKey'
      //Console.Write("{0} ", c);
    }
/****/
 
/****  This works to read stdin but still blocks... * /
    TextReader trIn = Console.In;
    while( trIn.Peek() != -1 )
    {
      //Console.WriteLine("trIn.Length= {0} ", trIn.Length );
      // `System.IO.TextReader' does not contain a definition for `Length'
      c = (char)trIn.Read();
      Console.Write("{0} ", c );
    }
    trIn.close();
/ ****/
 
/**** This works to read stdin but still blocks the same:
 
    StreamReader srIn= new StreamReader(Console.OpenStandardInput());
    while( srIn.Peek() != -1 )
    {
      //Console.WriteLine("srIn.Length= {0} ", srIn.Length );
      //  System.IO.StreamReader' does not contain a definition for `Length'
      //  
      c = (char)srIn.Read();
      Console.Write("{0} ", c);
      if(c == 'x') break;  
    }
    srIn.Close();
****/
 
/****
    if( Console.In )  
      Error: Cannot implicitly convert type `System.Console.In' to `bool'
****
    if( (bool)Console.In )
      Error: Cannot convert type `System.Console.In' to `bool'
****
    if( Console.In.Good )  // no member "Good"
      Console.Write("Console.In ");
    else 
      Console.Write("NO Console.In ");
****/
 
    //Console.WriteLine("Console.In= {0}", Console.In ); 
    // ouptput:  Console.In= System.IO.SynchronizedReader
 
    //Console.WriteLine("Console.OpenStandardInput().Length= {0}", 
    //                                   Console.OpenStandardInput().Length );
    // exception: The stream does not support seeking (with or without piped data)
 
    //Console.WriteLine("Console.In.Length= {0}", Console.In.Length ); 
    // error: System.IO.TextReader' does not contain a definition for `Length'
  }
}

There are so many objects and methods in C# I get lost.
I had thought that this would be doable in C# but maybe not. (I wonder why not)
I guess I'll have to get user to indicate input method as a CL argument.
Thanks for the ideas, Howard

[GaryTexmo]

Have a look here...
http://www.csharpfriends.com/Forums/...x?PostID=53551

You can check to see if a key is available with Console.KeyAvailable, then you can read it out of the stream at that point.

Does that help any?

[HowardL]

So Console.KeyAvailable seems to be set to false if there is no piped data
BUT Surprise! I can't tell if it DOES detect piped data because when the
console is in the graphics mode, any piped data will cause an exception!

I can read from command line from within the program if there is no piped data.!

-> gmcs peek_stdin-2.cs
-> mono peek_stdin-2.exe
-> echo -n "dude" | mono peek_stdin-2.exe

Unhandled Exception: System.IO.IOException: Not a tty.
at System.TermInfoDriver.Init () [0x00000]
at System.TermInfoDriver.Clear () [0x00000]
at System.ConsoleDriver.Clear () [0x00000]
at System.Console.Clear () [0x00000]
at MyProg.Main (System.String[] args) [0x00000]

Here is what I've been testing with:

using System;
 
class MyProg
{
  static void Main(string[] args)
  {
    char c;
 
    /* So here we start with some graphics mode commands: */
    Console.Clear();
    Console.SetCursorPosition( 0, 0);
    Console.Write("-----test-----\n");
 
    if( Console.KeyAvailable)
    {
      Console.WriteLine("got stdin");
    }
    else
    {
      Console.WriteLine("Don't got stdin");
      while( true ).                         
      {
        c = (char)Console.Read();
        Console.Write("{0} ", c);
        if(c == '\n') break;
      }
    }
    */
    //c = (char)Console.Read();    // hold window open to see output 
  }
}

even a single Console.Clear() will cause the exception!
Oh well. maybe I'm missing something.
Thanks for the sugestion though.

[Plater]

Console.OpenStandardInput().Length should be 0 unless there is data to be read from the standard input.

[HowardL]

That works for you?

#### If I try either this:
int x = (int)Console.OpenStandardInput().Length ;

#### or this
Console.WriteLine("Console.OpenStandardInput().Len gth= {0} ",
Console.OpenStandardInput().Length );

### and run with either this:
-> mono peek_stdin-2.exe

#### or this:
-> echo "Hello" | mono peek_stdin-2.exe

#### I get this each time:
Unhandled Exception: System.NotSupportedException: The stream does not support seeking

-----
I am using mono on linux and compiling with either:

mcs progname.cs
or
gmcs progname.cs

Both build the code with no questions warnings or errors.
Maybe mono is the problem?
Or am I missing something as far as how to use Console.OpenStandardInput().Length?

[Plater]

You are correct, seems the stdin doesn't support the length.
Console.KeyAvailable worked for me though.

[HowardL]

> You are correct, seems the stdin doesn't support the length.
Good, then mono is not the problem.

> Console.KeyAvailable worked for me though.
hmm, and you can pipe data to that without getting an exception?
Are you using Windows?

[Plater]

Yes I am in windows. I would have thought there would be no difference on this matter in mono.
KeyAvailable seems to be similar to C's kbhit()

[HowardL]

KeyAvailable seems to be similar to C's kbhit()

I guess they haven't written it yet...
Oh well, I'll just give that quest up and have the user indicate if data is in stdin or file thruough a command line arg:

 using System;
 
class myprog
{
  static void Main(string[] args)
  {
    string input;
 
    if(args.Length == 0)
    {
      Console.WriteLine("\n     ***** Error: no arguments supplied *****\n"+
        "Usage:  {0}  filin  \n\n" +
        "...where \"filin\" is an input file name \n"+
        "or '-' if input is to be from keyboard or pipe (|) or redirect (<).",
        Environment.GetCommandLineArgs() );
 
       return;
    }
 
    if(args[0] == "-")
    {
      Console.WriteLine("\nReading data from stdin: ");
      input = Console.ReadLine();
      Console.WriteLine(input);
    }
    else
    {
      Console.WriteLine("sorry , haven't written code for file input yet");
    }
  }
}
/*
 
csprogs>  mcs pipe_detect.cs
 
csprogs>  mono pipe_detect.exe
 
     ***** Error: no arguments supplied *****
Usage:  /mnt/e/csprogs/pipe_detect.exe  filin  
 
...where "filin" is an input file name 
or '-' if input is to be from keyboard or pipe (|) or redirect (<).
 
-----
 
csprogs>  echo -n "123.5 543.2 456.7 987.4" | mono pipe_detect.exe -
 
Reading data from stdin: 
123.5 543.2 456.7 987.4
 
-----
 
csprogs>  cat > xfile
123.5 543.2 456.7 987.4
 
csprogs>   mono pipe_detect.exe - <  xfile
 
Reading data from stdin: 
123.5 543.2 456.7 987.4
 
-----
 
csprogs>   mono pipe_detect.exe xfile
sorry , haven't written code for file input yet
 
-----:)
*/

Thanks for your help.