pass stdout as file name for command line util?

Solution 1: Using process substitution

The most convenient way of doing this is by using process substitution. In bash the syntax looks as follows:

foo -o >(other_command)

(Note that this is a bashism. There's similar solutions for other shells, but bottom line is that it's not portable.)

Solution 2: Using named pipes explicitly

You can do the above explicitly / manually as follows:

1. Create a named pipe using the mkfifo command.

   mkfifo my_buf
   

2. Launch your other command with that file as input

   other_command < my_buf
   

3. Execute foo and let it write it's output to my_buf

   foo -o my_buf
   

Solution 3: Using /dev/stdout

You can also use the device file /dev/stdout as follows

foo -o /dev/stdout | other_command

You could use the magic of UNIX and create a named pipe :)

1. Create the pipe

   $ mknod -p mypipe
   

2. Start the process that reads from the pipe

   $ second-process < mypipe
   

3. Start the process, that writes into the pipe

   $ foo -o mypipe
   

For the sake of making stackoverflow happy let me write a long enough sentence because my proposed solution is only 18 characters long instead of the required 30+

foo -o /dev/stdout

Named pipes work fine, but you have a nicer, more direct syntax available via bash process substitution that has the added benefit of not using a permanent named pipe that must later be deleted (process substitution uses temporary named pipes behind the scenes):

foo -o >(other command)

Also, should you want to pipe the output to your command and also save the output to a file, you can do this:

foo -o >(tee output.txt) | other command