单项选择题
A.[-n $x] B.[-l $x] C.[-s $x] D.[-z $x]
A.[-x file] B.[-f file] C.[-r file] D.[-w file]
A.[-f/var/log] B.[-d/var/log] C.[-r/var/log] D.(-x/var/log)
A.if(x==y) B.if[$x-eq$y] C.if[$x-gt$y] D.if[x-lty]
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