主要是在Makefile中看到了这种字符($@)，不理解含义，查阅了一下，跟shell中意义不一样：$@ -is the name of the target currently being processed.
$< -is the name of the first dependency.
顺便提下shell下的$# Stores the number of command-line arguments that were passed to the shell program.
$? Stores the exit value of the last command that was executed. $0 Stores the first word of the entered command (the name of the shell program). $* Stores all the arguments that were entered on thecommand line ($1 $2 ...). "$@" Stores all the arguments that were entered on the command line, individually quoted ("$1" "$2" ...).