What does the “$#” special parameter mean in Bash?

Question

I\'ve come across the code

if [ $# -eq 1  ]; then
   echo \"usage: Phar ~/flashmem ~/archive\"
   exit
fi

I\'ve never come across [

Answer 1

The $# returns the number of parameters passed as arguments.

#!/bin/bash
echo $#

Now

./testess.sh test1 test2 test3

This returns 3.

./testess.sh test1 test2 test3 test4 test5

This returns 5.

So in your code, if $# equals the number one (just one argument passed), execute the echo command.

Answer 2

It Expands to the number of positional parameters in decimal.

(copied from man bash, under Special Parameters).