Shell script variables and string interception

Variable Description:
$$ The shell itself PID (ProcessID)
$! PID of the Shell's last running background process
$? End code of 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" $1″ "$2″ ... All parameters are output in the form "$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, the $ $ is the 2nd parameter ...

string interception:
string interception of Linux is useful. There are eight ways.
Suppose there is a variable var=http://www.sharelinux.com/index.html
1. # Intercept, delete the left character, leave the right character.
Echo ${var#*//}
where Var is the variable name and the # is an operator, *//indicates that the first//number and all characters on the left are deleted from the left.
Delete http: //
The result is: www.sharelinux.com/index.html
2. # # Intercept, delete the left character and leave the right character.
Echo ${var##*/}
##*/indicates that the last (rightmost) one/number and all characters to the left are deleted from the left.
that is, delete http://www.sharelinux.com/
The result is index.html .
3.% Intercept, delete right character, leave left character
Echo ${var%/*}
%/* indicates that the first/second and right characters are deleted from the right.
The result is: http://www.sharelinux.com
4. The percent number intercept, delete the right character, leave the left character
Echo ${var%%/*}
%%/* indicates that the last (leftmost) one/number and right character are deleted from the right.
The result is: http:
5. Start with the first few characters on the left and the number of characters
Echo ${var:0:5}
0 represents the first character on the left and 5 indicates the total number of characters.
The result is: http:
6. Start with the first few characters on the left and continue to the end.
Echo ${var:7}
7 means that the 8th character on the left begins, until the end.
The result is: www.sharelinux.com/index.html
7. Start with the first few characters on the right and the number of characters
Echo ${var:0-7:3}
0-7 means that the seventh character starts at the right, and 3 indicates the number of characters.
The result is: 123
8. Start with the first few characters on the right and continue to the end.
Echo ${var:0-7}
The expression starts at the seventh character on the right and continues to the end.
The result is: index.html
Note: (The first character on the left is denoted by 0, and the first character on the right is denoted by 0-1)

This article is from the "Sanctuary of Calm" blog, please make sure to keep this source http://masters.blog.51cto.com/6516495/1642200

Shell script variables and string interception