如何测试进程是否存在于 Bash 中？
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How to test if a process exists in Bash?
提问by at.
I want to make sure nodeis running when logging in. So in my .bashrcfile I have:
我想确保node在登录时正在运行。所以在我的.bashrc文件中我有：
pkill node
sleep 1
node server.js &
Of course, that doesn't check if nodeis running... it simply kills it and starts it up again. Instead I'd like something like this:
当然，这不会检查是否node正在运行......它只是杀死它并再次启动它。相反，我想要这样的东西：
node_process = $(pidof node)
if [not_exists node_process]; then
node server.js &
fi
The problem is the not_existsmethod doesn't seem to exist :). How do I test the existence of a number or string in Bash and is this the best way to ensure node is up and running upon login?
问题是该not_exists方法似乎不存在:)。如何在 Bash 中测试数字或字符串是否存在，这是确保节点在登录时启动并运行的最佳方法吗？
回答by chepner
You can check if a string is empty using -z:
您可以使用以下命令检查字符串是否为空-z：
node_process_id=$(pidof node)
if [[ -z $node_process_id ]]; then
node server.js &
fi
pidofreturns nothing if no matching processes are found, so node_process_idwould be set to an empty string.
pidof如果找不到匹配的进程，则不返回任何内容，因此node_process_id将设置为空字符串。
