what is the role of the backslash in this command why it is used and the dollar sign?

Question

PRICE_PER_APPLE=5
echo "The price of an Apple today is: \$HK $PRICE_PER_APPLE" 

Why the dollar sign and backslash is used in the argument? What is the meaning of sha-bang !#? And what does it do the bash script can you me the best example to easy get understanding of it?

Answer 1

$HK in double quotes would be expanded to the value of the variable $HK. By preceding it with a backslash, you escape the expansion, so the literal string $HK is echoed (probably meaning Hong Kong Dollars).

There's no "sha-bang" in your example. It's usually spelt "shebang" and it contains the characters you mentioned in the reversed order. It tells the system what interpreter to use to run the script. For example,

#! /bin/bash

will be interpreted by /bin/bash, while

#! /usr/bin/sed

will be interpreted by /usr/bin/sed.