Explanation of the meaning of shell variable $#,$@,$0,$1,$2 in Linux

The meaning of several variables in a common shell with a $ symbol:

Difference:@ *

• Same point: All parameters are referenced
• Different points: only in double quotes. Suppose that three parameters were written when the script was run (stored in123) "*" is equivalent to "123"（Mass transferHanded a parameter number ) < /span> 1 &quot ; &quot; " > 1 "&NBSP; " 2 " " (three parameters passed)

Variable Description:
$$
The PID of the shell itself (ProcessID)
$!
PID of the Shell's last running background process
$?
End code of the last Run command (return value)
$-
Flag at a glance using the SET command
$*
All parameter lists. such as "$*" in the Case of "" ", in the form of" $ $ ... $n "output all parameters.
[Email protected]
All parameter lists. such as "[email protected]" with "" "in the case, with" $ "" $ "... All parameters are output in the form "$n".
$#
Number of arguments added to the shell
The file name of the shell itself
$1~ $n
Each parameter value added to the shell. $ $ is the 1th parameter, and the $ = is the 2nd parameter ....

Example:

1 #!/bin/bash   2 #   3 printf  "The complete list is %s\n" "$$"   4 printf  "The complete list is %s\n" "$!"   5 printf  "The complete list is %s\n" "$?"   6 printf  "The complete list is %s\n" "$*"   7 printf  "The complete list is %s\n" "[email protected]"   8 printf  "The complete list is %s\n" "$#"   9 printf  "The complete list is %s\n" "$0" 10 printf  "The complete list is %s\n" "$1" 11 printf  "The complete list is %s\n" "$2

Results:

$ bash test .sh 123456 QQ The complete list  is 22216 The complete list  is The complete list  is 0 The complete list  is 123456 QQ The complete list  is 123456 The complete list  is QQ The complete list  is 2 The complete list  is params .sh The complete list  is 123456 The complete list  is QQ

Linux shell variable $#,[email protected], $0,$1,$2 meaning explanation