Special variables in the shell $ $ $# $$ $! $? meaning __shell Script

$: The name of the executing script $* and $@: Return all parameters to $#: The number of arguments $_: represents the last parameter of the previous command $$: The PID $! that represents the command that was last executed: The PID $?: A flag that represents the success of the previous command, or $ if the execution succeeds? is 0, otherwise not 0.
Write a script test [wang@localhost desktop]$ vim test1.sh #!/bin/sh echo number:$# "echo" Name:$0 "echo" first:$1 "echo" Secon D:$2 "echo" argure1:$@ "ret=" $@ "ret1=$@ echo" $ret "echo" $ret 1 "echo" argure2:$* "echo" Arg:$_ "echo" result:$ "echo" P Id:$$ "echo" pid:$! "
[Wang@localhost Desktop]$ chmod +x test1.sh [wang@localhost desktop]$ ./test1.sh a b c number:3 Name:./test1 . SH first:a second:b argure1:a b c A b c a b c Argure2:a b c Arg:argure2:a b c result:0 pid:14973 PID:
[Wang@localhost Desktop]$ ./test1.sh "A" "B" "C" except the PID is not the same, the other results are the same.
After testing, the following doubts were expressed: $*: Give the argument list in double quotes $@: Return each argument with double quotes
Note: The meaning of the $ $ is different in the shell and awk. Shell: First word of the command line awk: current record