Terminal or not Terminal

[A. Clay Stephenson]

The -t test does more than simply look to see if the file descriptor is open, it tests to see whether or not, it is assiciated with a tty (terminal) device. It can be used, for example, to test whether a process is interactive or if stdin is coming from a pipe.

Try this trivial test:

Create my.sh,
if [[ -t 0 ]]
then
echo "Terminal"
else
echo "Not Terminal"
fi

Now invoke it thusly:
my.sh

and then
echo "Dummy" | my.sh


Man test for details. You could also use the more familiar "if [ -t 0 ]" syntax but the double brackets are more efficient because it uses the POSIX (or Korn) shell's internal test rather than forking the external test command.

[Marty Metras]

Ah! I see.
So when I pipe to something, the something is not part on the part of the current process it is a subprocess that is not part of the terminal process. Well kinda.
Thanks for the man test. Didn't know tat was there.

Marty

[Michael Schulte zur Sur]

Hi Marty,

stdin,stdout,stderr are not allways associated with a device. Not only when you pipe, also when you redirect <> or run a process in the backgound, lets say as a crontab or at job.

have fun,

Michael