The genuine way to give parameters to a command is to give them on the program call, which is made on the command line.

There a other ways to achieve parameter passing to a command, such as using a specific file, or using environment variables.

On the other hand, standard input is commonly used to give _data_ to process, not parameters.

As a matter of facts, [date] command does make any use of standard input.
So you can pipe _anything_ you want, [date] won’t ever use it. You might have pipe (with echo) any text, [date] won’t use it.

Make sure by Reading The Fantastic Manual,
by issuing the command: man date

Do you think you get the point?

But we do not get the same output from echo “–version” | date
and date –version. Can you please explain why the output is different.

Right way to give parameters on command line is:

date –version

When you want a program to use some input from a pipe is:

echo “some text used as input” | tr “[[:lower:]]” “[[:upper:]]”

But these are two really different functionalities. They are not equivalent at all, so they cannot yield the same.

– Philippe

I think I used that one on proprietary AIX or may be on HP-UX UNIX box. The month field is four characters long, left side. Same goes for the day (2 chars long). It will not work on *GNU coreutils*. You can try them on HP-UX or AIX and should provide output as follows:

mmmm    dd HH:MM