[email protected]

[email protected] is one of the Bash special parameters. It can only be referenced as follows

echo "[email protected]"

However, assignment to it is not allowed:

@=foo

Purpose

[email protected] expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a separate word. That is, "[email protected]" is equivalent to "$1" "$2" .. "$n". 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 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, "[email protected]" and [email protected] expand to nothing (i.e., they are removed).

Examples

Create a shell script called testpara.sh:

#!/bin/bash
echo "\[email protected] with double quotes : [email protected]"
echo \$@ without double quotes : [email protected]
echo

echo "\[email protected] with double quotes \$1 is : $1"
echo "\[email protected] with double quotes \$2 is : $2"
echo "\[email protected] with double quotes \$3 is : $3"
echo

echo \$@ without double quotes \$1 is : $1
echo \$@ without double quotes \$2 is : $2
echo \$@ without double quotes \$3 is : $3
echo

Run it as follows:

chmod +x testpara.sh
./testpara.sh one two three four

Sample outputs:

[email protected] with double quotes : one two three four
[email protected] without double quotes : one two three four

[email protected] with double quotes $1 is : one
[email protected] with double quotes $2 is : two
[email protected] with double quotes $3 is : three

[email protected] without double quotes $1 is : one
[email protected] without double quotes $2 is : two
[email protected] without double quotes $3 is : three

Now run it again as follows (note the double quotes when calling the script):

./testpara.sh one two "three four"

Sample outputs:

[email protected] with double quotes : one two three four
[email protected] without double quotes : one two three four

[email protected] with double quotes $1 is : one
[email protected] with double quotes $2 is : two
[email protected] with double quotes $3 is : three four

[email protected] without double quotes $1 is : one
[email protected] without double quotes $2 is : two
[email protected] without double quotes $3 is : three four

Consider the following for loop example (testpara1.sh):

#!/bin/bash
echo "*** Processing \[email protected] without double quote:"
for f in [email protected]
do
	echo "\$f = $f"
done

echo "*** Processing \[email protected] with double quote:"
for f in "[email protected]"
do
	echo "\$f = $f"
done

Save and close the file. Run it as follows:

chmod +x testpara1.sh
./testpara.sh1 one two "three four"

Sample outputs:

*** Processing [email protected] without double quote:
$f = one
$f = two
$f = three
$f = four
*** Processing [email protected] with double quote:
$f = one
$f = two
$f = three four