Extract and delete the first occurrence of the XML tag multiple times

Question

I have a XML file of little huge size. I have been provided with that and all I need to do is a extract some values in between the XML tags. Since I don't have the XML parser utility available in my machines. I am looking for an alternate method.

To start with, there is a XML tag <capacity> </capacity> which repeats n number of time in the XML file and in between this XML tags there are many other different tags as well.

I have to get each occurrence of <capacity> </capacity> XML tag separately and then parse through that and extract the values under them.

<subcolumns><capacity><name>45.90</name>
<index>0</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>
<capacity><name>57.09</name>
<index>1</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>
<capacity><name>55</name>
<index>2</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>
</subcolumns>

So the logic which I thought was to find the first occurrence of a <capacity> </capacity> XML tag and print it to a temp file and then delete that first occurrence.

<capacity><name>45.90</name>
<index>0</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>

Henceforth when this is done for the second time the new pair of <capacity> </capacity> XML tag is taken into consideration. So this has to repeat for multiple times until the last <capacity> </capacity> tag is found. And each time this part is extracted the data will be changing and that can be extracted.

Now all I want is to select the first occurrence of <capacity> </capacity> XML tag from the master XML file & print it to temp file and delete that part.

And this is what I tried and nothing worked for me.

sed -n '2,${/<capacity>\(.*\)<\/capacity>/\1/p;q;}' "<input XML file>" >> temp.txt

My further idea is to take that temp file for processing and extract the values which I need to under the capacity tags. For which I have already written the logic and it is working fine.

Answer 1

Using XML parsers is the right way for manipulating XML documents.

xmlstarlet solution:

xmlstarlet sel -t -c '//capacity[1]' -n yourxml > temp.txt 
&& xmlstarlet ed -d '//capacity[1]' yourxml > tmp.xml && mv tmp.xml yourxml 

---

cat temp.txt
<capacity><name>45.90</name>
<index>0</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>

---

• xmlstarlet sel -t -c '//capacity[1]' -n yourxml > temp.txt - extracts the first capacity tag declaration and redirects the output to temp.txt

• xmlstarlet ed -d '//capacity[1]' yourxml > tmp.xml - deletes the first capacity tag from the document (via -d delete action) and redirects the modified document content to temporary file tmp.xml

• mv tmp.xml yourxml - replace the initial xml document with its modified version

Answer 2

Since you don't have an xml parser , give a try to this one with gnu awk:

$ awk -v RS="<subcolumns>|</capacity>" 'NR==2{gsub(/^\n/,"");print $0 RT;exit}' file.xml
<capacity><name>45.90</name>
<index>0</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>

Why this works:
in awk you can set a custom record / line separator. In our example we use either <subcolumns> or </capacity>

As a result with a customized record separator we can achieve this format:

$ awk -v RS="<subcolumns>|</capacity>" '{gsub(/^\n/,"");print NR,$0 RT}' file.xml
1 <subcolumns>
2 <capacity><name>45.90</name>
<index>0</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>
3 <capacity><name>57.09</name>
<index>1</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>
4 <capacity><name>55</name>
<index>2</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>
5 </subcolumns>

PS: NR = Number or Record/Line. RT=Record Separator used.

Accordingly you can print any <capacity></capacity> block by adjusting the NR number:

$ awk -v RS="<subcolumns>|</capacity>" 'NR==4{gsub(/^\n/,"");print $0 RT}'
<capacity><name>55</name>
<index>2</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>

Accordingly, if you need to skip a <capacity> section (i.e first capacity section) you can just do :

$ awk -v RS="<subcolumns>|</capacity>" '{gsub(/^\n/,"")}NR!=2{print $0 RT}'
<subcolumns>
<capacity><name>57.09</name>
<index>1</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>
<capacity><name>55</name>
<index>2</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>
</subcolumns>

Answer 3

chunk=2; # specify the tag chunk number here which must be > 0
perl -l -0777ne "print((m{(<capacity>.*?</capacity>)}sg)[${chunk:-1}-1])" yourxmlfile

---

Results

<capacity><name>57.09</name>
<index>1</index>
<value_type>String</value_type>
<ignore_case_flag>1</ignore_case_flag>
<hidden_flag>0</hidden_flag>
<exclude_from_parse_flag>1</exclude_from_parse_flag>
</capacity>