what is the difference between $1 and "$1" in bash script?

example

while [ -n "$1" ]
do
  something
done

can i write $1 instead of "$1"? And what is the difference between
user=alexander and user="alexander"? Thanks

Answer

$ var="two words"
$ function num_args() { echo "${#}"; }
$ num_args $var
2
$ num_args "$var"
1

The difference between $A and "$A" is how word breaks are treated with respect to passing arguments to programs and functions.

Imagine script that works on files (let's say moves them around):

$ cat my-move

#! /bin/sh
# my-move


src=${1}
dst=${2}

# ... do some fancy business logic here

mv ${src} ${dst}

$ my-move "some file" other/path

As the code stands now (no quotes) this script is broken as it will not handle file paths with spaces in them correctly.

(Following thanks to @CharlesDuffy)

Additionally quoting matters when handling glob patterns:

$ var='*'
$ num_args "$var"
1
$ num_args $var
60

Or:

$ shopt -s failglob

$ var='[name]-with-brackets'
$ echo $var
bash: no match: [name]-with-brackets
$ echo "$var"
[name]-with-brackets