Home » What is the difference between $* and $@?

What is the difference between $* and $@?

Solutons:


When they are not quoted, $* and $@ are the same. You shouldn’t use either of these, because they can break unexpectedly as soon as you have arguments containing spaces or wildcards.


"$*" expands to a single word "$1c$2c...". Usually c is a space, but it’s actually the first character of IFS, so it can be anything you choose.

The only good use I’ve ever found for it is:

join arguments with comma (simple version)

join1() {
    typeset IFS=,
    echo "$*"
}

join1 a b c   # => a,b,c

join arguments with the specified delimiter (better version)

join2() {
    typeset IFS=$1   # typeset makes a local variable in ksh (see footnote)
    shift
    echo "$*"
}

join2 + a b c   # => a+b+c

"$@" expands to separate words: "$1" "$2" ...

This is almost always what you want. It expands each positional parameter to a separate word, which makes it perfect for taking command line or function arguments in and then passing them on to another command or function. And because it expands using double quotes, it means things don’t break if, say, "$1" contains a space or an asterisk (*).


Let’s write a script called svim that runs vim with sudo. We’ll do three versions to illustrate the difference.

svim1

#!/bin/sh
sudo vim $*

svim2

#!/bin/sh
sudo vim "$*"

svim3

#!/bin/sh
sudo vim "$@"

All of them will be fine for simple cases, e.g. a single file name that doesn’t contain spaces:

svim1 foo.txt             # == sudo vim foo.txt
svim2 foo.txt             # == sudo vim "foo.txt"
svim2 foo.txt             # == sudo vim "foo.txt"

But only $* and "$@" work properly if you have multiple arguments.

svim1 foo.txt bar.txt     # == sudo vim foo.txt bar.txt
svim2 foo.txt bar.txt     # == sudo vim "foo.txt bar.txt"   # one file name!
svim3 foo.txt bar.txt     # == sudo vim "foo.txt" "bar.txt"

And only "$*" and "$@" work properly if you have arguments containing spaces.

svim1 "shopping list.txt" # == sudo vim shopping list.txt   # two file names!
svim2 "shopping list.txt" # == sudo vim "shopping list.txt"
svim3 "shopping list.txt" # == sudo vim "shopping list.txt"

So only "$@" will work properly all the time.


typeset is how to make a local variable in ksh (bash and ash use local instead). It means IFS will be restored to its previous value when the function returns. This is important, because the commands you run afterward might not work properly if IFS is set to something non-standard.

Short answer: use "$@" (note the double quotes). The other forms are very rarely useful.

"$@" is a rather strange syntax. It is replaced by all the positional parameters, as separate fields. If there are no positional parameters ($# is 0), then "$@" expands to nothing (not an empty string, but a list with 0 elements), if there is one positional parameter then "$@" is equivalent to "$1", if there are two positional parameters then "$@" is equivalent to "$1" "$2", etc.

"$@" allows you to pass down the arguments of a script or function to another command. It is very useful for wrappers that do things like setting environment variables, preparing data files, etc. before calling a command with the same arguments and options that the wrapper was called with.

For example, the following function filters the output of cvs -nq update. Apart from the output filtering and the return status (which is that of grep rather than that of cvs), calling cvssm on some arguments behaves like calling cvs -nq update with these arguments.

cvssm () { cvs -nq update "$@" | egrep -v '^[?A]'; }

"$@" expands to the list of positional parameters. In shells that support arrays, there is a similar syntax to expand to the list of elements of the array: "${array[@]}" (the braces are mandatory except in zsh). Again, the double quotes are somewhat misleading: they protect against field splitting and pattern generation of the array elements, but each array element ends up in its own field.


Some ancient shells had what is arguably a bug: when there were no positional arguments, "$@" expanded to a single field containing an empty string, rather than into no field. This led to the workaround ${1+"$@"} (made famous via the Perl documentation). Only older versions of the actual Bourne shell and the OSF1 implementation are affected, none of its modern compatible replacements (ash, ksh, bash, …) are. /bin/sh is not affected on any system that was released in the 21st century that I know of (unless you count Tru64 maintenance release, and even there /usr/xpg4/bin/sh is safe so only #!/bin/sh script are affected, not #!/usr/bin/env sh scripts as long as your PATH is set up for POSIX compliance). In short, this is a historical anecdote that you don’t need to worry about.


"$*" always expands to one word. This word contains the positional parameters, concatenated with a space in between. (More generally, the separator is the first character of the value of the IFS variable. If the value of IFS is the empty string, the separator is the empty string.) If there are no positional parameters then "$*" is the empty string, if there are two positional parameters and IFS has its default value then "$*" is equivalent to "$1 $2", etc.

$@ and $* outside quotes are equivalent. They expand to the list of positional parameters, as separate fields, like "$@"; but each resulting field is then split into separate fields which are treated as file name wildcard patterns, as usual with unquoted variable expansions.

For example, if the current directory contains three files bar, baz and foo, then:

set --         # no positional parameters
for x in "$@"; do echo "$x"; done  # prints nothing
for x in "$*"; do echo "$x"; done  # prints 1 empty line
for x in $*; do echo "$x"; done    # prints nothing
set -- "b* c*" "qux"
echo "$@"      # prints `b* c* qux`
echo "$*"      # prints `b* c* qux`
echo $*        # prints `bar baz c* qux`
for x in "$@"; do echo "$x"; done  # prints 2 lines: `b* c*` and `qux`
for x in "$*"; do echo "$x"; done  # prints 1 lines: `b* c* qux`
for x in $*; do echo "$x"; done    # prints 4 lines: `bar`, `baz`, `c*` and `qux`

Here is a simple script to demonstrates the difference between $* and $@:

#!/bin/bash

test_param() {
  echo "Receive $# parameters"
  echo Using '$*'

  echo
  for param in $*; do
    printf '==>%s<==n' "$param"
  done;

  echo
  echo Using '"$*"'
  for param in "$*"; do
    printf '==>%s<==n' "$param"
  done;

  echo
  echo Using '$@'
  for param in $@; do
    printf '==>%s<==n' "$param"
  done;

  echo
  echo Using '"$@"';
  for param in "$@"; do
  printf '==>%s<==n' "$param"
  done
}

IFS="^${IFS}"

test_param 1 2 3 "a b c"

Output:

% cuonglm at ~
% bash test.sh
Receive 4 parameters

Using $*
==>1<==
==>2<==
==>3<==
==>a<==
==>b<==
==>c<==

Using "$*"
==>1^2^3^a b c<==

Using $@
==>1<==
==>2<==
==>3<==
==>a<==
==>b<==
==>c<==

Using "$@"
==>1<==
==>2<==
==>3<==
==>a b c<==

In array syntax, there is no difference when using $* or $@. It only make sense when you use them with double quotes "$*" and "$@".

Related Solutions

Joining bash arguments into single string with spaces

[*] I believe that this does what you want. It will put all the arguments in one string, separated by spaces, with single quotes around all: str="'$*'" $* produces all the scripts arguments separated by the first character of $IFS which, by default, is a space....

AddTransient, AddScoped and AddSingleton Services Differences

TL;DR Transient objects are always different; a new instance is provided to every controller and every service. Scoped objects are the same within a request, but different across different requests. Singleton objects are the same for every object and every...

How to download package not install it with apt-get command?

Use --download-only: sudo apt-get install --download-only pppoe This will download pppoe and any dependencies you need, and place them in /var/cache/apt/archives. That way a subsequent apt-get install pppoe will be able to complete without any extra downloads....

What defines the maximum size for a command single argument?

Answers Definitely not a bug. The parameter which defines the maximum size for one argument is MAX_ARG_STRLEN. There is no documentation for this parameter other than the comments in binfmts.h: /* * These are the maximum length and maximum number of strings...

Bulk rename, change prefix

I'd say the simplest it to just use the rename command which is common on many Linux distributions. There are two common versions of this command so check its man page to find which one you have: ## rename from Perl (common in Debian systems -- Ubuntu, Mint,...

Output from ls has newlines but displays on a single line. Why?

When you pipe the output, ls acts differently. This fact is hidden away in the info documentation: If standard output is a terminal, the output is in columns (sorted vertically) and control characters are output as question marks; otherwise, the output is...

mv: Move file only if destination does not exist

mv -vn file1 file2. This command will do what you want. You can skip -v if you want. -v makes it verbose - mv will tell you that it moved file if it moves it(useful, since there is possibility that file will not be moved) -n moves only if file2 does not exist....

Is it possible to store and query JSON in SQLite?

SQLite 3.9 introduced a new extension (JSON1) that allows you to easily work with JSON data . Also, it introduced support for indexes on expressions, which (in my understanding) should allow you to define indexes on your JSON data as well. PostgreSQL has some...

Combining tail && journalctl

You could use: journalctl -u service-name -f -f, --follow Show only the most recent journal entries, and continuously print new entries as they are appended to the journal. Here I've added "service-name" to distinguish this answer from others; you substitute...

how can shellshock be exploited over SSH?

One example where this can be exploited is on servers with an authorized_keys forced command. When adding an entry to ~/.ssh/authorized_keys, you can prefix the line with command="foo" to force foo to be run any time that ssh public key is used. With this...

Why doesn’t the tilde (~) expand inside double quotes?

The reason, because inside double quotes, tilde ~ has no special meaning, it's treated as literal. POSIX defines Double-Quotes as: Enclosing characters in double-quotes ( "" ) shall preserve the literal value of all characters within the double-quotes, with the...

What is GNU Info for?

GNU Info was designed to offer documentation that was comprehensive, hyperlinked, and possible to output to multiple formats. Man pages were available, and they were great at providing printed output. However, they were designed such that each man page had a...

Set systemd service to execute after fstab mount

a CIFS network location is mounted via /etc/fstab to /mnt/ on boot-up. No, it is not. Get this right, and the rest falls into place naturally. The mount is handled by a (generated) systemd mount unit that will be named something like mnt-wibble.mount. You can...

Merge two video clips into one, placing them next to each other

To be honest, using the accepted answer resulted in a lot of dropped frames for me. However, using the hstack filter_complex produced perfectly fluid output: ffmpeg -i left.mp4 -i right.mp4 -filter_complex hstack output.mp4 ffmpeg -i input1.mp4 -i input2.mp4...

How portable are /dev/stdin, /dev/stdout and /dev/stderr?

It's been available on Linux back into its prehistory. It is not POSIX, although many actual shells (including AT&T ksh and bash) will simulate it if it's not present in the OS; note that this simulation only works at the shell level (i.e. redirection or...

How can I increase the number of inodes in an ext4 filesystem?

It seems that you have a lot more files than normal expectation. I don't know whether there is a solution to change the inode table size dynamically. I'm afraid that you need to back-up your data, and create new filesystem, and restore your data. To create new...

Why doesn’t cp have a progress bar like wget?

The tradition in unix tools is to display messages only if something goes wrong. I think this is both for design and practical reasons. The design is intended to make it obvious when something goes wrong: you get an error message, and it's not drowned in...