bash 带有空白/空 grep 的语句返回吗？
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While Do Statement with blank/empty grep return?
提问by bikerben
This is the code for my foobar.sh:
这是我的 foobar.sh 的代码：
!#/bin/bash
while [ 1 ]
do
pid=`ps -ef | grep "mylittleprogram" | grep -v grep | awk ' {print }'`
echo $pid
if [ "$pid"="" ]
then
echo "Process has ended lets get this show on the road..."
exit
else
echo "Process has not ended yet"
fi
sleep 6
done
I'm basically running a infinate loop which will execute command X once a monitored process has ended but I end up getting the following message as my script loops:
我基本上正在运行一个无限循环，一旦受监控的进程结束，它将执行命令 X 但我最终在脚本循环时收到以下消息：
./foobar.sh: line 7: [: missing `]'
Process has not ended yet
Is there a way of making the script accept that zero feed back will trigger my 'Then' statement and execute command X since it is not liking the current method.
有没有办法让脚本接受零反馈将触发我的“Then”语句并执行命令 X，因为它不喜欢当前的方法。
回答by A.H.
Instead of
代替
if [ "$pid"="" ]
please try
请尝试
if [ "$pid" = "" ]
The whitespace is around =is important.
周围的空白=很重要。
You can also try
你也可以试试
if [ -z "$pid" ]
回答by sehe
I'd do
我会做
while pgrep -fl "mylittleprogram"; do sleep 6; done
exit # process has ended
(pgrep is in package psmiscIIRC)
（pgrep 在psmiscIIRC包中）
I've just tested it. You could redirect the output of pgrepto /dev/nullif you wanted the waiting to be silent. Add some more spice to make things uninterruptible:
我刚刚测试过了。如果您希望等待静默，您可以将pgrepto的输出重定向/dev/null。添加一些更多的香料，使事情不间断：
{
trap "" INT
while pgrep -fl "mylittleprogram" >/dev/null
do
sleep 6
done
true
} && exit
回答by chx
The zero test is if [ -z "$pid" ]
零测试是 if [ -z "$pid" ]
回答by JRFerguson
Instead of the nebulous matching provided by:
而不是提供的模糊匹配：
pid=`ps -ef | grep "mylittleprogram" | grep -v grep | awk ' {print }'`
...and the archaic backtick syntax, consider this which matches the process basename exactly and produces an output format of your choice (here, the process pid if it exists):
...以及古老的反引号语法，请考虑这与进程基本名称完全匹配并生成您选择的输出格式（此处为进程 pid，如果存在）：
pid=$(ps -C mylittleprogram -opid=)
Then, as noted, simply test for an empty value:
然后，如前所述，只需测试一个空值：
[ -z "${pid" ] && echo "no process" || echo "I live as $pid"
The equal sign following the output element name suppresses the heading that you would normally get. Manpages are your friend.
输出元素名称后面的等号抑制了您通常会得到的标题。联机帮助页是您的朋友。
