shell中单引号和双引号的问题

lala=hehe
echo "'$lala'"
输出:'hehe'
这样就可以把参数拼接到where条件中

echo "select a from table where a='$lala' "
输出：select a from table where a='hehe'

这里注意下这种情况的输出

echo "select a from table where a="'$lala'" "
输出：select a from table where a=$lala
执行效果和下面这种方式一样
echo select a from t '$lala'
输出：select a from table where a=$lala