shell判断一个变量是否为空方法总结

#!/bin/sh
para1=
if [ ! -n "$para1" ]; then
  echo "IS NULL"
else
  echo "NOT NULL"
fi

#!/bin/sh
para1=
if [ ! $para1 ]; then
  echo "IS NULL"
else
  echo "NOT NULL"
fi

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

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