Adding XML element in XML file using sed command in shell script

Question

I am using sed command to insert an xml element into the existing xml file.

I have xml file as

<Students>
    <student>
        <name>john</>
        <id>123</id>
    </student>
    <student>
        <name>mike</name>
        <id>234</id>
    </student>
</Students>

I want to add new elememt as

    <student>
        <name>NewName</name>
        <id>NewID</id>
    </student>

So my new xml file will be

<Students>
    <student>
        <name>john</>
        <id>123</id>
    </student>
    <student>
        <name>mike</name>
        <id>234</id>
    </student>
    <student>
        <name>NewName</name>
        <id>NewID</id>
    </student>
</Students>

For this I have written shell script as

#! /bin/bash

CONTENT="<student>
            <name>NewName</name>
            <id>NewID</id>
        </student>"

#sed -i.bak '/<\/Students>/ i \ "$CONTENT" /root/1.xml
sed -i.bak '/<\/Students>/ i \'$CONTENT'/' /root/1.xml

I am getting error as

sed: can't read <name>NewName</name>: No such file or directory
sed: can't read <id>NewID</id>: No such file or directory
sed: can't read </student>: No such file or directory

And in the xml file, only <student> is added. The remaining elements are not added. Does anyone know why this error?

Several tools exist to manipulate XML files. Use those instead of regular expressions. — devnull, Apr 23 '14 at 04:37
@devnull would be nice of you to list one (or two) of those tools — zaitsman, Sep 04 '17 at 06:13

Farvardin · Accepted Answer · 2018-11-06T07:33:37.050

9

change this:

CONTENT="<student>
            <name>NewName</name>
            <id>NewID</id>
        </student>"

to this:

CONTENT="<student>\n<name>NewName</name>\n<id>NewID</id>\n</student>"

and then:

C=$(echo $CONTENT | sed 's/\//\\\//g')
sed "/<\/Students>/ s/.*/${C}\n&/" file

edited Nov 06 '18 at 07:33

answered Apr 23 '14 at 04:54

Farvardin

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If my tag is New Name, then how can handle whitespace here? '\t' will add one tab and I need single whitespace – ajay_t Apr 23 '14 at 04:55
1

@USer007 You can escape the space character with backslash-space – not2savvy Oct 18 '21 at 10:00

score 5 · Answer 2 · answered Apr 23 '14 at 05:31

You cannot have an unescaped newline in sed replacement text, that is $CONTENT in your example. sed uses the newline just like the shell does, to terminate a command.

If you need a newline in the replacement text, you need to precede it with a backslash.

There is another way to add text using the r option. For example:

Lets say your main file is;

$ cat file
<Students>
    <student>
        <name>john</>
        <id>123</id>
    </student>
    <student>
        <name>mike</name>
        <id>234</id>
    </student>
</Students>

You text you want to add is in another file (not variable):

$ cat add.txt
    <student>
        <name>NewName</name>
        <id>NewID</id>
    </student>

You can do (using gnu sed):

$ sed '/<\/Students>/{ 
    r add.txt
    a \</Students>
    d 
}' file
<Students>
    <student>
        <name>john</>
        <id>123</id>
    </student>
    <student>
        <name>mike</name>
        <id>234</id>
    </student>
    <student>
        <name>NewName</name>
        <id>NewID</id>
    </student>
</Students>

However, having given this option, it is still a very bad idea to parse xml with regular expression. It makes the solution very fragile and easy to break. Consider this as a learning exercise only.

score 1 · Answer 3 · answered Apr 23 '14 at 10:56

1

This might work for you (GNU sed & Bash):

CONTENT='    <student>\
    <name>NewName</name>\
    <id>NewID</id>\
</student>'

sed '/<\/Students>/i\'"$CONTENT" file

Alternatively, put the new students in a file and:

sed '/<\/Students>/e cat new_student_file' file

answered Apr 23 '14 at 10:56

potong

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Here if tag is like New Name, then how can I handle this whitespace. – ajay_t Apr 23 '14 at 10:58
@Optimus for the variable just remember that the last character of each line (but the last) must end in `\\`. For the file solution just write the text as you see it. – potong Apr 23 '14 at 11:02

Adding XML element in XML file using sed command in shell script

3 Answers3

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