Note-shell Special variables

Positional variables:

$: Gets the file name of the current execution shell, including the script path if the script is executed with a path

$n: Gets the n=1..9 parameter value of the currently executing shell script, which represents the file name of the script when n is 0, and if n is greater than 9, the curly braces are enclosed in ${10}.

[email protected] ~]# vim q.sh
echo $ $4 $ $6 $7 $8 $9 ${10} ${11} ${12} ${13} ${14} ${15}

Results of the output

[email protected] ~]# sh q.sh {a.. Z
A b c d e F g h i j k l m n o

$*: Treats all command-line parameters as a single string, equivalent to "$1$2$3", "$*"

[email protected]: Treat each parameter of the command line as a separate string, equivalent to "$!" $ "$" This is the best way to pass parameters to other programs because he retains any whitespace embedded in each parameter

Note : The above differences are limited to double quotes, i.e. "$*" and "[email protected]"

Example:[[email protected] ~]# Set--"I am" from Hunan

[email protected] ~]# echo $#

3

Example :

[[email protected]~]# for I in "$*";d o echo $i;d one with double quotes, as a parameter output
I am from Hunan
[[email protected]~]# for i in "[email protected]";d o echo $i;d one with double quotes, independent output
I am
From
Hunan

Example:

[[email protected] ~]# for I;do Echo $i;d One removes the in variable list, equivalent in "[email protected]"

I am

From

Hunan

Example:

[[email protected] ~]# for i in $*;d o echo $i;d one without double quotes, all parameters are output, and the first parameter "I Am" is also opened

I
Am
From
Hunan

$?: Gets the return value that executes the last instruction (0 is successful, nonzero is failed) This variable is very common.

Cases:

echo $?

$#: Gets the total number of parameters after the currently executing shell script.

Enterprise Case Control the number of user parameters :

                   [ [email protected]  ~]# vim q1.sh

[$#-ne 2] && {
echo "Pls input number"
Exit 1----> assigns a value to the current shell's $? variable.

}
echo "Thanks!"

Note-shell Special variables