How to insert text after a certain string in a file with variables

Question

I have these variables:

file_path="/home/dir/file.xml"
string="<host mac='0A:00:DD:D2:00:02' name='vfp-20vr' ip='10.10.1.122'/>"

This is the content of file.xml

<network>
  <name>br-ext</name>
  <forward mode='route'/>
  <bridge name='br-ext' stp='on' delay='0'/>
  <mac address='52:54:00:9f:a0:00'/>
  <ip address='10.10.1.11' netmask='255.255.255.0'>
    <dhcp>
      <host mac='0A:AA:FF:C1:A1:EE' name='vsrxa-1' ip='10.10.1.21'/>
      <host mac='0A:AA:FF:C1:A2:EE' name='vsrxa-2' ip='10.10.1.22'/>
      <host mac='0A:AA:FF:C1:B1:EE' name='vsrxb-1' ip='10.10.1.23'/>
      <host mac='0A:AA:FF:C1:B2:EE' name='vsrxb-2' ip='10.10.1.24'/>
      <host mac='0A:AA:FF:C1:C1:EE' name='vsrxc-1' ip='10.10.1.25'/>
      <host mac='0A:AA:FF:C1:C2:EE' name='vsrxc-2' ip='10.10.1.26'/>
      <host mac='0A:AA:FF:C1:D1:EE' name='vsrxd-1' ip='10.10.1.27'/>
      <host mac='0A:AA:FF:C1:D2:EE' name='vsrxd-2' ip='10.10.1.28'/>
    </dhcp>
  </ip>
</network>

I would like to add the $string right after the <dhcp> flag, something like this:

...
<dhcp>
      <host mac='0A:00:DD:D2:00:02' name='vfp-20vr' ip='10.10.1.122'/>
      <host mac='0A:AA:FF:C1:A1:EE' name='vsrxa-1' ip='10.10.1.21'/>
...

I tried using sed "/\dhcp\/a $string $file_path" in my bash script with no success...

Does anyone know how I can achieve this?

Arnaud Valmary · Accepted Answer · 2022-05-06 11:56:10Z

You are not too far:

sed -i "/<dhcp>/a \ \ \ \ \ \ ${string}" "${file_path}"

-i to change input file
/<dhcp>/ to select only dhcp open tag
(\ ) * 6 to indent string content

Result:

<network>
  <name>br-ext</name>
  <forward mode='route'/>
  <bridge name='br-ext' stp='on' delay='0'/>
  <mac address='52:54:00:9f:a0:00'/>
  <ip address='10.10.1.11' netmask='255.255.255.0'>
    <dhcp>
      <host mac='0A:00:DD:D2:00:02' name='vfp-20vr' ip='10.10.1.122'/>
      <host mac='0A:AA:FF:C1:A1:EE' name='vsrxa-1' ip='10.10.1.21'/>
      <host mac='0A:AA:FF:C1:A2:EE' name='vsrxa-2' ip='10.10.1.22'/>
      <host mac='0A:AA:FF:C1:B1:EE' name='vsrxb-1' ip='10.10.1.23'/>
      <host mac='0A:AA:FF:C1:B2:EE' name='vsrxb-2' ip='10.10.1.24'/>
      <host mac='0A:AA:FF:C1:C1:EE' name='vsrxc-1' ip='10.10.1.25'/>
      <host mac='0A:AA:FF:C1:C2:EE' name='vsrxc-2' ip='10.10.1.26'/>
      <host mac='0A:AA:FF:C1:D1:EE' name='vsrxd-1' ip='10.10.1.27'/>
      <host mac='0A:AA:FF:C1:D2:EE' name='vsrxd-2' ip='10.10.1.28'/>
    </dhcp>
  </ip>
</network>

sseLtaH · Accepted Answer · 2022-05-06 12:11:16Z

Using sed

$ sed  "/<dhcp>/{p;s|\( \+\).*|\1  $string|;}" file
<network>
  <name>br-ext</name>
  <forward mode='route'/>
  <bridge name='br-ext' stp='on' delay='0'/>
  <mac address='52:54:00:9f:a0:00'/>
  <ip address='10.10.1.11' netmask='255.255.255.0'>
    <dhcp>
      <host mac='0A:00:DD:D2:00:02' name='vfp-20vr' ip='10.10.1.122'/>
      <host mac='0A:AA:FF:C1:A1:EE' name='vsrxa-1' ip='10.10.1.21'/>
      <host mac='0A:AA:FF:C1:A2:EE' name='vsrxa-2' ip='10.10.1.22'/>
      <host mac='0A:AA:FF:C1:B1:EE' name='vsrxb-1' ip='10.10.1.23'/>
      <host mac='0A:AA:FF:C1:B2:EE' name='vsrxb-2' ip='10.10.1.24'/>
      <host mac='0A:AA:FF:C1:C1:EE' name='vsrxc-1' ip='10.10.1.25'/>
      <host mac='0A:AA:FF:C1:C2:EE' name='vsrxc-2' ip='10.10.1.26'/>
      <host mac='0A:AA:FF:C1:D1:EE' name='vsrxd-1' ip='10.10.1.27'/>
      <host mac='0A:AA:FF:C1:D2:EE' name='vsrxd-2' ip='10.10.1.28'/>
    </dhcp>
  </ip>
</network>

The fourth bird · Accepted Answer · 2022-05-06 13:38:46Z

You could use a pattern to match the <dhcp> part and capture the leading spaces.

Then append the next string, substitute with the full match for the last pattern followed by a newline and the backreference to keep the same indenting.

From that point on, you can extend it with your own indenting.

sed "/^\([[:space:]]*\)<dhcp>/{N;s##&\n\1  $string#}" "$file_path"

Explanation

/^$[[:space:]]*$<dhcp>/ Natch start of string, capture optional spaces and match <dhcp>
N Append the next line to the pattern space
s substitute
## The last matched pattern (I have changed the delimiter of the substitute to #)
&\n\1 Replace with the full match, newline and a backreference to group 1 containing the indenting and add your own indenting

Output

<network>
  <name>br-ext</name>
  <forward mode='route'/>
  <bridge name='br-ext' stp='on' delay='0'/>
  <mac address='52:54:00:9f:a0:00'/>
  <ip address='10.10.1.11' netmask='255.255.255.0'>
    <dhcp>
      <host mac='0A:00:DD:D2:00:02' name='vfp-20vr' ip='10.10.1.122'/>
      <host mac='0A:AA:FF:C1:A1:EE' name='vsrxa-1' ip='10.10.1.21'/>
      <host mac='0A:AA:FF:C1:A2:EE' name='vsrxa-2' ip='10.10.1.22'/>
      <host mac='0A:AA:FF:C1:B1:EE' name='vsrxb-1' ip='10.10.1.23'/>
      <host mac='0A:AA:FF:C1:B2:EE' name='vsrxb-2' ip='10.10.1.24'/>
      <host mac='0A:AA:FF:C1:C1:EE' name='vsrxc-1' ip='10.10.1.25'/>
      <host mac='0A:AA:FF:C1:C2:EE' name='vsrxc-2' ip='10.10.1.26'/>
      <host mac='0A:AA:FF:C1:D1:EE' name='vsrxd-1' ip='10.10.1.27'/>
      <host mac='0A:AA:FF:C1:D2:EE' name='vsrxd-2' ip='10.10.1.28'/>
    </dhcp>
  </ip>
</network>

Splinter1984 · Accepted Answer · 2022-05-06 12:05:51Z

1

try this

#! /bin/bash

file_path="$HOME/test.xml"
content="<host>b</host>"

c=$(echo $content | sed 's/\//\\\//g')
sed "/<\/dhcp>/ s/.*/${c}\n&/" $file_path

answered May 6, 2022 at 12:05

Splinter1984

237 bronze badges

Comments

M. Nejat Aydin · Accepted Answer · 2022-05-06 12:19:08Z

1

Using bash and sed's a (append) command:

sed '/^[[:blank:]]*<dhcp>[[:blank:]]*$/a'$'\\\n'"$string" "$file_path"

answered May 6, 2022 at 12:19

M. Nejat Aydin

10.3k1 gold badge10 silver badges22 bronze badges

1 Comment

M. Nejat Aydin Over a year ago

@Thefourthbird Those leading whitespaces are not significant in an xml document. They are for human readability.

ufopilot · Accepted Answer · 2022-05-06 13:22:30Z

strings="      STRING1...\n      STRING2...\n      ...\n" 
match="<dhcp>"  
awk -v m="$match" -v s="$strings" '{ print; if($1 == m) printf s }' input_file

<network>
  <name>br-ext</name>
  <forward mode='route'/>
  <bridge name='br-ext' stp='on' delay='0'/>
  <mac address='52:54:00:9f:a0:00'/>
  <ip address='10.10.1.11' netmask='255.255.255.0'>
    <dhcp>
      STRING1...
      STRING2...
      ...
      <host mac='0A:AA:FF:C1:A1:EE' name='vsrxa-1' ip='10.10.1.21'/>
      <host mac='0A:AA:FF:C1:A2:EE' name='vsrxa-2' ip='10.10.1.22'/>
      <host mac='0A:AA:FF:C1:B1:EE' name='vsrxb-1' ip='10.10.1.23'/>
      <host mac='0A:AA:FF:C1:B2:EE' name='vsrxb-2' ip='10.10.1.24'/>
      <host mac='0A:AA:FF:C1:C1:EE' name='vsrxc-1' ip='10.10.1.25'/>
      <host mac='0A:AA:FF:C1:C2:EE' name='vsrxc-2' ip='10.10.1.26'/>
      <host mac='0A:AA:FF:C1:D1:EE' name='vsrxd-1' ip='10.10.1.27'/>
      <host mac='0A:AA:FF:C1:D2:EE' name='vsrxd-2' ip='10.10.1.28'/>
    </dhcp>
  </ip>
</network>

seeker · Accepted Answer · 2022-05-06 16:00:14Z

0

For a similar task I use xmlstarlet. Obviously you got $string from a xml source. Thus you can use xmlstarlet to get mac, name and ip values. Let's assume you got them. You can then add a new host into $file_path like this:

xmlstarlet edit --inplace \
  --insert /network/ip/dhcp/host[1] --type elem --name new_host --value "" \
  --insert //new_host --type attr --name mac  --value $new_host_mac \
  --insert //new_host --type attr --name name --value $new_host_name \
  --insert //new_host --type attr --name ip   --value $new_host_ip \
  --rename //new_host --value host \
  $file_path

answered May 6, 2022 at 16:00

seeker

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