sed search and replace after xml tag

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# 1  
Question sed search and replace after xml tag

Hi All,
I'm new to sed.

In following XML file
   <interface type='direct'>
      <mac address='52:54:00:86:ce:f6'/>
      <source dev='eno1' mode='bridge'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    <interface type='direct'>
      <mac address='52:54:00:ab:d5:77'/>
      <source dev='eno2' mode='bridge'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>

i have add one new xml tag after <source dev='eno1' mode='bridge'/>, which is <target dev='New1'/>.

for i in `eno1 eno2 eno3 eno4`
        echo "Updating macvtap device names for $i"
	sed -i.bak "/source dev='$i'/a <target dev='New$cnt'/>" 
    	cnt=`expr $cnt + 1`

The above is not working. Please let me know how to do it?

Moderator's Comments:
Mod Comment Please use code tags as required by forum rules!

Last edited by RudiC; 06-03-2016 at 11:50 AM.. Reason: Added code tags.
# 2  
Do you have in mind that eno# is not the only form of Ethernet device names? eno# is only the naming for onboard network cards.

It can be too be a name like ens1 or ens3f0 ore a few other combinations. See

# 3  
Yes, i'm aware of that.

All i wanted is give a persistent name to the macvtap devices using this script.

I have taken care of finding the interface names, now only thing have to do is in that xml, <source dev='eno1' mode='bridge/>, append the next line with specific target dev names, using this sed command.
# 4  
You want to cycle the for loop through each given word
for i in eno1 eno2 eno3 eno4

Optimization: your shell certainly does not need an external call of expr for integer arithmetics

# 5  
to clarify, the following is command substition(call a command and get the output of it).

`eno1 eno2 eno3 eno4`

As you just want the bare words, omit the apostrophe.

And for the nit-picker in me, this works to too:


This User Gave Thanks to stomp For This Post:
# 6  
Do you want to use a counter (which, BTW, you did not initialize and thus is the empty string for the first loop) or the source device's number?

for i in eno1 eno2 eno3 eno4
    do    echo "Updating macvtap device names for $i"
          sed "/source dev='$i'/a <target dev='New${i#${i%?}}'/>"  XML_file

This User Gave Thanks to RudiC For This Post:
# 7  

Interesting construct Smilie Another way of expressing...

${i: -1}

...and i just got confused with ...


which does not work as desired because :- is default value assignment.
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