What is the difference between "$@" and "$*" in Bash?

Question

It seems to me that they both store all the command-line arguments.

So is there a difference between the two?

Solution 1

The difference is subtle; "$*" creates one argument separated by the $IFS variable, while "$@" will expand into separate arguments. As an example, consider:

for i in "$@"; do echo "@ '$i'"; done
for i in "$*"; do echo "* '$i'"; done

When run with multiple arguments:

./testvar foo bar baz 'long arg'
@ 'foo'
@ 'bar'
@ 'baz'
@ 'long arg'
* 'foo bar baz long arg'

For more details:

http://www.gnu.org/software/bash/manual/bashref.html#Special-Parameters

$*

Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, it expands to a single word with the value of each parameter separated by the first character of the IFS special variable. That is, "$*" is equivalent to "$1c$2c...", where c is the first character of the value of the IFS variable. If IFS is unset, the parameters are separated by spaces. If IFS is null, the parameters are joined without intervening separators.

$@

Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a separate word. That is, "$@" is equivalent to "$1" "$2" .... If the double-quoted expansion occurs within a word, the expansion of the first parameter is joined with the beginning part of the original word, and the expansion of the last parameter is joined with the last part of the original word. When there are no positional parameters, "$@" and $@ expand to nothing (i.e., they are removed).

Solution 2

A key difference from my POV is that "$@" preserves the original number of arguments. It's the only form that does.

For example, if file my_script contains:

#!/bin/bash

main()
{
   echo 'MAIN sees ' $# ' args'
}

main $*
main $@

main "$*"
main "$@"

### end ###

and I run it like this:

my_script 'a b c' d e

I will get this output:

MAIN sees  5  args
MAIN sees  5  args
MAIN sees  1  args
MAIN sees  3  args

Comments

[爱国者]

If $@ and $* are not put into double quotes("") , the expands behavior look the same.

[erik]

Wow, this answer is really illustrative! Thanks.

[glenn jackman]

That's a good way to illustrate it, as the number of arguments.

[Totem]

But why do the parens around $* and $@ make a difference here?

[Art Swri]

@Totem I'm assuming you said 'parens' but mean double-quotes. The difference between "$*" and $* is that the quotes keep the expansion of $* as a single string while having no quotes allows the parts of $* to be treated as individual items. This is the general meaning of double quotes; the behaviour is not specific to $* and $@. As an aside, the difference between single quotes and double quotes is that substitutions (such as the expansion of $*) are performed in double quotes but are not performed within single quotes. (The result of '$*' is just $*, the 2-character literal value.)

[Totem]

@ArtSwri Your answer is much appreciated. I did indeed mean double-quotes

[Trismegistos]

@爱国者 When not quoted behaviour is different. See stackoverflow.com/a/12316565/1169741 for code example