Confusion re: expr deprecation for strings

[apennebaker]

Shellcheck says to replace expr ..., as expr is deprecated. For mathematical expressions, I can use $((...)) instead. But what should I use for string expressions?

FizzBuzz example:

mcandre/toys#2 (comment)

[koalaman]

Is this just to write the value? Use echo for that.

[apennebaker]

I want to write a shell function that returns a string, without printing it (very functional programming style). But it's not easy, as shell functions normally only return exit codes.

For FizzBuzz, I gave up, and had the fizz function go ahead and print the value instead of returning it. My Lisp senses are tingling, but whatcha gonna do...

[koalaman]

Writing to stdout is how you return data from functions. The caller decides what happens to it, whether it's captured or merged with the caller's stdout. It's perfectly functional.

[apennebaker]

Interesting. I suppose there are ways to redirect the output before/when the function is executed, so that the user doesn't see the string in the real STDOUT?

[koalaman]

Yes. you can capture/expand the data with variable=$(somefunction), pipe it with somefunction | otherfunction, redirect it with somefunction > somefile, and there are process substitutions and coprocs, and they can all be combined and nested arbitrarily.

In lisp/scheme, (+ 2 3) will print 5 to the screen if you run it from a repl, but not if you use it as a sub-expression unless the function implicitly or explicitly returns it unmodified. That's the same thing.

There's no "real stdout" in bash, just like there's no "real return value" in lisp. There's just your own return value/stdout, and what the caller did with it.

[apennebaker]

Pipe |! Genius!