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Standard Output and Standard Error

Programs can be written to send their output to either the standard
output device or the standard error device. Sometimes programs
are written to send different types of output to each device. You
can't always tell which is which because, by default, both devices
are the screen.
The Windows 2000 Type command illustrates the difference.
When used with wildcards (something you can't do with the Type
command in MS-DOS or Windows 9x), Type sends the name of
each matching file to standard error and sends the contents of the
file to standard output. Because they both go to the screen, you see
a nice display with each file name followed by its contents.
However, if you try to redirect output to a
file like this:
type *.bat > std.out
the file names still appear on your screen because standard error is
still directed to the screen. Only the file contents are redirected to
Std.out.
Windows 2000 allows you to qualify the redirection symbol by
preceding it with a number. Use 1> (or simply >) for standard
output and 2> for standard error. For example:
type *.bat 2> err.out
This time the file contents go to the screen and the names are
redirected to Err.out. You can redirect both to separate files with
this command line:
type *.bat 2> err.out 1> std.out

The Pipe Symbol
The pipe symbol (|) is used to send, or pipe, the output of one
program to a second program as the second program's input.
Piping is commonly used with the More utility, which displays
multiple screens of output one screenful at a time. For example:
help dir | more
This command line uses the output of Help as the input for More.
The More command filters out the first screenful of Help output,
sends it to the screen as its own output, and then waits for a
keypress before sending more filtered output.