linux++：Linux

1、判断一个变量是否为空 的方法

1、变量通过" "引号引起来
#!/bin/sh
para1=
if [ ! -n "$para1" ]; then
  echo "IS NULL"
else
  echo "NOT NULL"
fi 

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2、直接通过变量判断
#!/bin/sh
para1=
if [ ! $para1 ]; then
  echo "IS NULL"
else
  echo "NOT NULL"
fi 

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3、使用test判断
#!/bin/sh
dmin=
if test -z "$dmin"
then
  echo "dmin is not set!"
else  
  echo "dmin is set !"
fi

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4、使用""判断
#!/bin/sh 
dmin=
if [ "$dmin" = "" ]
then
  echo "dmin is not set!"
else  
  echo "dmin is set !"
fi