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Batch Script Input and Output

Input and Output​

There are three universal "files" for keyboard input, screen text printing, and screen error printing.

  • The Standard Input file, known as stdin, contains the input to the program/script.
  • The Standard Output file, known as stdout, is used to write the output to be displayed on the screen.
  • The Standard Error file, known as stderr, contains all the error messages to be displayed on the screen.

Each of these three standard files, otherwise known as the standard streams, are referenced using numbers:

  • stdin is file 0
  • stdout is file 1
  • stderr is file 2

Redirecting Output​

A common practice in batch scripting is to send the output of a program to a log file.

You use the > operator to send, or redirect, stdout or stderr to another file. The following example shows how this can be done.

In the following example, the stdout of the command dir C:\ is redirected to the file list.txt.

dir C:\ > list.txt

If you append the number 2 to the redirection filter, then it would redirect the stderr to the file lists.txt.

dir C:\ 2> list.txt

You can even combine the stdout and stderr streams using the file number and the & prefix.

dir C:\ > lists.txt 2>&1

Suppressing Program Output​

The pseudo-file NUL is used to discard the output of a program.

The following example shows that the output of the dir command is discarded by sending it to NUL.

dir C:\ > NUL

Stdin​

To work with the stdin, a workaround must be used. This can be done by redirecting the command prompt stdin, called CON.

The following example shows how you can redirect the output to a file called lists.txt. After you execute the below command, the command prompt will take all the input entered by user till it gets an EOF character. Later, it sends all the input to the file lists.txt.

TYPE CON > lists.txt

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