$$
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 name of the shell itself
$1~ $n
Each parameter value added to the shell. $ $ is the 1th parameter, and the $ = is the 2nd parameter ....
Let's start by writing a simple script that will explain the meaning of each variable after execution.
# Touch Variable
# VI Variable
The script reads as follows:
#!/bin/sh
echo "number:$#"
echo "Scname:$0"
echo "First: $ $"
echo "Second:$2"
echo "Argume:[email protected]"
Special usage of $0,$?,$! in shell