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I learned about the command line command test and read a few examples. One of them was obscure to me:

 test 100 -gt 99 && echo "Yes, that's true." || echo "No, that's false."

I understand it to this point:

test 100 -gt 99

evaluates whether 100 is greater than 99

echo "Yes, that's true." || echo "No, that's false."

If the expression turns out to be true do the command on the left of the double pipe symbol, otherwise do the right one.

I could not find any hint onto the &amp expression in the manual.

What is its purpose?

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  • 5
    It's a double-escaped &. It should say &&, not &&. Commented May 10, 2017 at 8:29
  • Today you'll learn: mojibake. :) Commented May 10, 2017 at 11:20

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& doesn't mean anything to test, it's the HTML entity for the ampersand &, which has a special meaning in HTML so it cannot be presented as-is. Where ever that snippet came from, the presentation is broken.

Decoding that character, the line should be 

test 100 -gt 99 && echo "Yes..." || echo "No..."

&& and || still don't have anything to do with test itself, but are conditional constructs for the shell. cmd1 && cmd2 runs first cmd1 then, if it returns a truthy value (zero), runs cmd2.

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