The last thing we'd like to discuss in this chapter is the here string. It is very similar to the here document (hence the name), but it deals with a single string, instead of a document (who would have thought!).

This construct, which uses the <<< syntax, can be used to supply text input to a command that perhaps normally only accepts input from stdin or a file. A good example for this is bc, which is a simple calculator (part of the GNU Project).

Normally, you use it in one of two ways: sending input to stdin via a pipe, or by pointing bc to a file:

reader@ubuntu:/tmp$ echo "2^8" | bc
256

reader@ubuntu:/tmp$ echo "4*4" > math
reader@ubuntu:/tmp$ bc math
bc 1.07.1
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'. 
16
^C
(interrupt) use quit to exit.
quit

When used with stdin, bc returns the result of the calculation. When used with a file, bc opens an interactive session, which we need to manually close by entering quit. Both ways seem a little too much work for what we want to achieve.

Let's look at how a here string fixes this:

reader@ubuntu:/tmp$ bc <<< 2^8
256

There we go. Just a simple here string as input (which is sent to stdin of the command), and we get the same functionality as an echo with a pipe. However, now it is just a single command, instead of a chain. Simple but effective, just the way we like it!