What is the difference between $@ and $* in linux shell script?

Question

In the book "Linux Shell Scripting Cookbook"

It says $@ expands as $1, $2, $3 and so on and $* expands as $1c$2c$3, where c is the first character of IFS.

What's the difference between $@ and $* and what IFS means?

Answer 1

IFS is the internal field separator, it basically means what the shell recognises as what seperates words.

So to run the following command

IFS=$'\n'

Would cause the shell to recognise new lines as seperators.

$ is the sign of something being assigned to a variable

However the numbers are reserved for script inputs.

So $1 would be a variable input, $2 would be a second variable input.

$@ is all of the parameters passed to the script.

So if you run the command

bash command.sh bork woof meow

This would be the value of the above listed variables

  $1 = bork
  $2 = woof
  $3 = meow
  $@ = bork woof meow

Answer 2

It's hard to improve on the explanation given in the manuals. For instance, dash(1) says:

$@

Expands to the positional parameters, starting from one. When the expansion occurs within double-quotes, each positional parameter expands as a separate argument. If there are no positional parameters, the expansion of @ generates zero arguments, even when @ is double-quoted. What this basically means, for example, is if $1 is “abc” and $2 is “def ghi”, then "$@" expands to the two arguments: "abc" "def ghi"

We can demonstrate the difference between $* and $@ with some examples:

$ set 1 "2 3"
$ printf '"%s"\n' "$@"
"1"
"2 3"
$ printf '"%s"\n' $@
"1"
"2"
"3"
$ printf '"%s"\n' "$*"
"1 2 3"
$ printf '"%s"\n' $*
"1"
"2"
"3"

The manual page also describes IFS:

IFS

Input Field Separators. This is normally set to ⟨space⟩, ⟨tab⟩, and ⟨newline⟩. See the White Space Splitting section for more details.