Using tee to create a log

[Wayne Conrad]

On Thu, 26 July 2001, Alan Dayley wrote:
> How does the piped program know that it is piped?  I would think that all
> it knows is that it is outputing to sdtout.  Who changes the data in the
> pipe?  The shell?

The shell doesn't mess with the data.  Instead, a program that cares can use an API to find out if its stdin is connected to a pipe, or to a file, or whatever, and then change its behavior accordingly.