How to pass the value of a variable to the stdin of a command?

Question

I\'m writing a shell script that should be somewhat secure i.e. does not pass secure data through parameters of commands and preferably does not use temporary files. How can

Answer 1

Just do:

printf "$my_var" | my_cmd

If the var doesn't contain spaces then the quotes may be omitted.
If using bash then you may also do:

echo -n "$my_var" | my_cmd

Avoid using echo without -n because it will pipe the vraiable with an added linebreak at the end.