unix变量赋值问题？求大神解答！

[xiaoshunzi2009]

a=`db2 -x "select 5 from syscat.procedures fetch first 2 row only with ur " `
echo "$a"
b=`echo "${a}"|wc -l`
echo "$b"
执行结果：2

c=`db2 -x "select 5 from syscat.procedures fetch first 2 row only with ur "|wc -l`
echo "$c"
执行结果为：1

a=`db2 -x "select 5 from syscat.procedures fetch first 2 row only with ur " `
echo "$a"
执行结果为：5
5
echo`db2 -x "select 5 from syscat.procedures fetch first 2 row only with ur " `
执行结果为：5 5

为什么会有这样的差异？变量的赋值过程是怎么样的？

[iasky]

你第二个是执行了wc -l计算行数的。

[xiaoshunzi2009]

但是第一个也是得出行数，只是分为两步了，为什么结果不一样？？

[xiaoshunzi2009]

补充一点： db2 -x "select 5 from syscat.procedures fetch first 2 row only with ur" | wc -l | read a echo "a=${a}" 执行结果： a=2

[ljc007]

方法A

a=`db2 -x "select 5 from syscat.procedures fetch first 2 row only with ur " `
echo "$a"

方法B

echo "`db2 -x "select 5 from syscat.procedures fetch first 2 row only with ur "`"

方法C

a=`db2 -x "select 5 from syscat.procedures fetch first 2 row only with ur " `
echo $a

方法D

echo `db2 -x "select 5 from syscat.procedures fetch first 2 row only with ur "`

方法A和方法B有双引号，效果相同。 方法A和方法B没有双引号，效果相同。 具体原因请参考： http://bbs.chinaunix.net/viewthread.php?tid=218853&page=4#pid1511745

[ljc007]

方法C和方法D没有双引号，效果相同。

[ljc007]

db2 -x "select 5 from syscat.procedures fetch first 2 row only with ur " > a.txt cat -n -A a.txt 把结果贴出来看看

[xiaoshunzi2009]

执行结果为： 1 5 2 5