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testing variables issue

 
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# 1  
Old 12-01-2011
testing variables issue
oh,i don't understand
my shell file like this
Code:
#!/bin/sh
#
#
testnum=$(ifconfig eth0|sed -n 8p|awk '{print $2}'|cut -c7-)
echo $testnum
sleep 2
echo $testnum
sleep 2
echo $testnum
sleep 2
echo $testnum

but the output was always the same value
like
Code:
[root@localhost test]# ./test.sh
3779052732
3779052732
3779052732
3779052732

why?
# 2  
Old 12-01-2011
The same reason this never changes:

Code:
testnum="qwertyuiop"
echo $testnum
sleep 2
echo $testnum
sleep 2
echo $testnum
sleep 2
echo $testnum

The value of "qwertyuiop" is copied into the variable and doesn't change until you set it to anything else.
# 3  
Old 12-01-2011
ok，i know you means，thank you
that’s difference
if the variable need to return the lastest value，i must recall it，right？
# 4  
Old 12-01-2011
Code:
echo $(ifconfig eth0|sed -n 8p|awk '{print $2}'|cut -c7-)
sleep 2
echo $(ifconfig eth0|sed -n 8p|awk '{print $2}'|cut -c7-)
sleep 2
echo $(ifconfig eth0|sed -n 8p|awk '{print $2}'|cut -c7-)
sleep 2
echo $(ifconfig eth0|sed -n 8p|awk '{print $2}'|cut -c7-)

Or better:

Code:
echo $(ifconfig eth0|sed -n 8p|awk '{print $2}'|cut -c7-)
for X in 1 2 3
do
        sleep 2
        echo $(ifconfig eth0|sed -n 8p|awk '{print $2}'|cut -c7-)
done

This User Gave Thanks to Corona688 For This Post:
flw521521
# 5  
Old 12-01-2011
thank you very much!
i think this unix forum is the most rigorous forum i had ever see,which make a big difference with China
thanks Corona688
ps:sorry for my poor english ^_^

---------- Post updated at 08:48 PM ---------- Previous update was at 08:18 PM ----------

do i need to do something to close this thread
# 6  
Old 12-02-2011
There is nothing like close in this forum.

I think, you can ignore the sed command also.

Code:
 
for X in 1 2 3
do
 echo $(ifconfig eth0|awk 'NR==8{print $2;exit}'|cut -c7-)
 sleep 2
done

This User Gave Thanks to itkamaraj For This Post:
flw521521
# 7  
Old 12-02-2011
ifconfig eth0|awk 'NR==8{print $2;exit}'|cut -c7-
it also the same result when i run the command like this
ifconfig eth0|awk 'NR==8{print $2}'|cut -c7-
can u tell me the effect of ";exit" ？



 
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