Is it possible to pass shell variable settings into an awk program?
There are two different ways to do this. The first involves simply expanding the variable where it is needed in the program. For example, to get a list of all ttys you’re using: who | awk ‘/^'”$USER”‘/ { print $2 }’ (1) Single quotes are usually used to enclose awk programs because the character ‘$’ is often used in them, and ‘$’ will be interpreted by the shell if enclosed inside double quotes, but not if enclosed inside single quotes. In this case, we *want* the ‘$’ in “$USER” to be interpreted by the shell, so we close the single quotes and then put the “$USER” inside double quotes. Note that there are no spaces in any of that, so the shell will see it all as one argument. Note, further, that the double quotes probably aren’t necessary in this particular case (i.e. we could have done who | awk ‘/^’$USER’/ { print $2 }’ (2) ), but they should be included nevertheless because they are necessary when the shell variable in question contains special characters or spaces. The second way t
