不会$！在Shell脚本中有意义 [英] Does $! mean something in shell scripting

问题描述

bash/shell脚本中是否存在 $！，如果是，请告知其用途.为什么在命令行上运行echo $!时，它会显示空白?

Does $! exists in bash/shell script, if yes, please inform for what it is used for. And why it gives blank when echo $! is run on the command line?

推荐答案

除了其他答案外，此回声

In addition to other answer, this echo

echo $!

如果您尚未在当前Shell中在后台运行任何进程，则将打印空白.如果您现在运行:

Will print blank if you haven't yet run any process in background in current shell. If you now run:

date &
echo $!

然后它将打印类似的内容(即上次执行的后台进程的进程ID):

Then it will print something like (i.e. process id of last executed background process):

47833

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