Comparison of $@ and $* in the shell

[email protected] ceshi]# cat test.sh

#!/bin/bash

# test.sh

echo "-------------ISF is set to \"-seperator\ "------------"

Ifs= "-seperator"; # Note that there is a minus sign (-) before Seperator

For i in "[email protected]"; Do echo "@ ' $i '"; Done

For i in "$*"; Do echo "* ' $i '"; Done

echo "-------------ISF is set to null------------------------"

ifs=

For i in "[email protected]"; Do echo "@ ' $i '"; Done

For i in "$*"; Do echo "* ' $i '"; Done

echo "-------------ISF is unset------------------------"

Unset IFS

For i in "[email protected]"; Do echo "@ ' $i '"; Done

For i in "$*"; Do echo "* ' $i '"; Done

Echo '---------$* and [email protected] is not put into double quotes ("")-------'

For i in [email protected]; Do echo "@ ' $i '"; Done

For i in $*; Do echo "* ' $i '"; Done

test.sh AA BB CC performs the following results:

[[Email protected] ceshi]# sh test.sh aa bb cc

-------------ISF is set to "-seperator"------------

@ ' AA '

@ ' BB '

@ ' CC '

* ' AA-BB-CC '

-------------ISF is set to null------------------------

@ ' AA '

@ ' BB '

@ ' CC '

* ' AABBCC '

-------------ISF is unset------------------------

@ ' AA '

@ ' BB '

@ ' CC '

* ' AA bb cc '

---------$* and [email protected] is not put into double quotes ("")-------

@ ' AA '

@ ' BB '

@ ' CC '

* ' AA '

* ' BB '

* ' CC '

Thus

1) when no double quotation marks (""), $*,[email protected] is expanded when the behavior is the same;

2) when $*,[email protected] are placed in double quotation marks ("");

2.1) If the value of the variable IFS is set and the value is not NULL, then $* is expanded with the first character of ${ifs} to concatenate all parameters (except the argument $), which is "$1c$2c$3c ...", where C represents the first character of ${ifs};

2.2) If the variable ifs is empty, then the $* is expanded to simply connect all parameters (except the parameter $), i.e. "$1$2$3 ..."

2.3) If the variable IFS is not defined, the $* is expanded with a space character to connect all parameters (except the parameter $), which is "$ $ ..."

However, the deployment of [email protected] is consistent with the absence of double quotes.

More examples of shell scripts:

#!/bin/bash

Set ' apple pie ' pears peaches

For I in $* #单引号被去掉, loop single character output #

Do Echo $i

Done

[Email protected] ceshi]# sh test1.sh

Apple

Pie

Pears

Peaches

--------------------------------------------------------------

#!/bin/bash

Set ' apple pie ' pears peaches

For i in "$*" #单引号被去掉 but as String once output #

Do Echo $i

Done

[Email protected] ceshi]# sh test2.sh

Apple pie Pears Peaches

-----------------------------------------------------------------

#!/bin/bash

Set ' apple pie ' pears peaches

For i in [email protected] #单引号被去掉, loop single character output #

Do Echo $i

Done

[Email protected] ceshi]# sh test3.sh

Apple

Pie

Pears

Peaches

-----------------------------------------------------------------

#!/bin/bash

Set ' apple pie ' pears peaches

For i in "[email protected]" #每个位置参数都将当成一个加引号的字符串: "Apple pie", "Pears", "Peaches" #

Do Echo $i

Done

[Email protected] ceshi]# sh test4.sh

Apple pie

Pears

Peaches

-----------------------------------------------------------------

test5.sh

Sum=0

for Var

In "[Email protected]"

Do

Let sum=sum+ $var

Done

echo "Sum= $sum"

./test1.sh 1 2 3

The result is sum=6

-----------------------------------------------------------------

test6.sh

Sum=0

for Var

In "$*"

Do

Let sum=sum+ $var

Done

echo "Sum= $sum"

./test2.sh 1 2 3

The result is Sum=1

-----------------------------------------------------------------

Analysis One:

Bash-x test1.sh

The results are as follows:

+ sum=0

+ for Var in ' [Email protected] '

+ Let Sum=sum+1

+ for Var in ' [Email protected] '

+ Let sum=sum+2

+ for Var in ' [Email protected] '

+ Let Sum=sum+3

+ Echo sum=6

Sum=6

You can see that for is executed three times, the for is bounded by "" because each parameter is surrounded by ""

Analysis Two:

Bash-x test2.sh

The results are as follows:

+ sum=0

+ for Var in ' "$*" '

+ Let sum=sum+1 2 3

+ Echo Sum=1

Sum=1

It can be seen that the loop executes only once, stating that the whole of $* is surrounded by "", not every parameter is "", so it only executes once

A more straightforward example is:

for Var

In "a B C"

Do

echo "${var}@"

Done

Print:

A b [email protected]

for Var

In "a" "B" "C"

Do

echo "${var}@"

Done

Print:

[Email protected]

[Email protected]

[Email protected]

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Comparison of [email protected] and $* in the shell