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Old 06-19-2014, 10:43 PM   #1
byran cheung
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the meaning in the script


I find the below script but I am not understand the function of this script .

Would advise what is the mean of "x" , what is the use of "x" in comparsion ? thanks

chk_running()
{
if [ "x"${PID} != "x" ]; then
echo "PID: "${PID}

if ..

else
RUNNING="F"
fi
else
RUNNING="F"
fi
}
 
Old 06-20-2014, 02:12 AM   #2
rhoekstra
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A weird way to determine whether variable PID is empty or not
 
Old 06-20-2014, 04:30 AM   #3
grail
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Not weird ... just old (like some of us)

[] is not as robust as the newer [[]] and hence it will throw an error if you test against an empty variable and no additional character.

Simple test is to take away the "x" from both sides and see what your 'if' does now
 
Old 06-20-2014, 04:49 AM   #4
rhoekstra
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I must admit 'weird' doesn't cut it.. but also, I'm very BASH minded, not old enough for the korn or SH shell languages to know the implications to test this way.

within BASH you can use '-n' or '-z' to verify non-empty or 'zero-length' of a string, which you should surround by "" not to have an exception.

I'm quite confident that "$PID" != "" would have sufficed as well which makes more sense...
 
  


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