Replace dynamic content in XML file

Question

Quick Summary: I need to create a Bash script to change the text within a node automatically every week. The script will match the node and replace the text inside them (if this is possible)? How would I do this?

Long Summary: I host a Minecraft server which has shops, each of which have their own .xml file in the /ShowcaseStandalone/ffs-storage/ directory. Every Sunday my server restarts and executes several commands into the terminal to reset several things. One thing that I am trying to make change is one of the shops. I am wanting to change the text in the node <itemstack> and the text in the node <price>. I am simply wanting to take text from a .txt file in a different folder, and insert it into that node. The problem is, that the text in the node will change every week. Is there any way to replace a specific line or text within two nodes using bash?

XML file:

<?xml version="1.0" encoding="UTF-8"?>
<scs-shop usid="cac8480951254352116d5255e795006252d404d9" version="2" type="storage">
    <enchantments type="string"/>
    <owner type="string">Chadward27</owner>
    <world type="string">Frisnuk</world>
    <itemStack type="string">329:0</itemStack>
    <activity type="string">BUY</activity>
    <price type="double">55.0</price>
    <locX type="double">487.5</locX>
    <locY type="double">179.0</locY>
    <locZ type="double">-1084.5</locZ>
    <amount type="integer">0</amount>
    <maxAmount type="integer">0</maxAmount>
    <isUnlimited type="boolean">true</isUnlimited>
    <nbt-storage usid="23dffac5fb2ea7cfdcf0740159e881026fde4fa4" version="2" type="storage"/>
</scs-shop>

Operating System: Linux Ubuntu 12.04

Solution 1

You can use xmlstarlet to edit a XML file in a shell like this :

xmlstarlet edit -L -u "/scs-shop/price[@type='double']" -v '99.66' file.xml

NOTE

• "/scs-shop/price[@type='double']" is a Xpath expression
• see xmlstarlet ed --help

Solution 2

The XML way is cool, but if you need to use normal bash tools, you can modify a line using sed. For instance:

PRICE=123
sed -i "s/\(<price.*>\)[^<>]*\(<\/price.*\)/\1$PRICE\2/" $XML_FILE_TO_MODIFY

This will replace the price with 123.

That sed command seems daunting, so let me break it down:

\(<price.*>\)[^<>]*\(<\/price.*\) is the pattern to match. \( ... \) are parenthesis for grouping. <price.*> matches the opening price tag. [^<>]* matches anything except angle brackets, and in this case will match the contents of the price tag. <\/price.* matches the end of the price tag. Forward slash is a delimiter in sed, so I escape it with a back slash.

\1$PRICE\2 is the text to replace the matched text with. \1 refers to the first matched parenthesis group, which is the opening price tag. $PRICE is the variable with the desired price in it. \2 refers to the second parenthesis group, in this case the closing tag.

Solution 3

I did not have the luxury of having xmlstarlet. I found a solution though simply by doing an inline replacement;

template-parameter.xml

<ns:Parameter>
    <ns:Name required="true">##-ParamName-##</ns:Name>
    <ns:Value>
        <ns:Text>##-ParamValue-##</ns:Text>
    </ns:Value>
</ns:Parameter>

Snippet

tokenName="foo"
tokenValue="bar"    

#Replace placeholders in parameter template element
myParamElement=$(cat template-parameter.xml)
myParamElement=${myParamElement//##-ParamName-##/$tokenName}
myParamElement=${myParamElement//##-ParamValue-##/$tokenValue}  

Result

<ns:Parameter>
    <ns:Name required="true">foo</ns:Name>
    <ns:Value>
        <ns:Text>bar</ns:Text>
    </ns:Value>
</ns:Parameter>

Comments

[Gilles Quenot]

So you just want to change usid from scs-shop tag ?

[Brian Cain]

XML manipulation using exclusively bash? Why limit yourself?

[Clucky]

@sputnick Sorry, I had to ad &lt and &gt tags because it killed my nodes, but no, I need to replace the text in the nodes "itemstack" and "price"

[Clucky]

@Brian-Cain Is there any other way to do this from terminal? Because these commands all execute upon the server shutting off

[Brian Cain]

I'd recommend python -- does your server have python installed, or can it? If not, java might be another option.

[Clucky]

@Brian-Cain I believe it does have python and it most certainly has Java. I heard you can do this using perl also; however, the only way I think perl would work for this specific script is if I also used RegEx (something I do not know). Also, am I tagging correctly? I'm brand new at this website, although I use it often for script references.

[tripleee]

The duplicate stackoverflow.com/questions/23560215/replace-xml-value-with-‌​sed has a few more answers if the ones here are unsuitable for some reason.

[Clucky]

I don't mean to make you do all the work for me, but I am a visual learner. How could I use this to replace "<price type="double">55.0<price>" with "<price type="double">25.0<price>"?

[Gilles Quenot]

I can give you the full syntax if you give me a valid XML

[Gilles Quenot]

You can test it like this : xmlstarlet val file.xml

[Clucky]

There, I fixed it. Sorry I'm brand new to stackoverflow so I don't know how to format correctly. But it should be a valid xml file now.

[Gilles Quenot]

Post edited with an example for price tag, it's quite very simple to adapt it for other tags

[Clucky]

Worked like a charm. Thank you so much!

[Gilles Quenot]

This is the wrong way. You can't realistically parse tag-based markup languages like HTML or XML using Bash, grep, sed, cut, etc. See codinghorror.com/blog/archives/001311.html (you know the blog website from SO creator ?) This is about HTML, but this is the same for XML...

[Dan Bliss]

If linux came with a good xml tool like xmlstarlet then I would agree that this is the wrong way. Until it does, sed is my go-to tool. Realistically, you can use sed in 99% of cases, including this one.

[Gilles Quenot]

I don't said "that don't work" but : "that's not reliable". In a simple case like this this seems "fine" for some people, but what happens when the XML will becomes more complicated with nested tags ? I'm talking about reliable way to makes things clean. sudo apt-get install xmlstarlet is not a big deal there.

[Dan Bliss]

"but I think that's just as wrongheaded as demanding every trivial HTML processing task be handled by a full-blown parsing engine" is a quote from the blog post you cite. Regardless, for the record: I prefer the xmlstarlet solution. But if xmlstarlet is not available, sed will get er done.

[BeniBela]

@sputnick: apt-get install is not so easy, e.g. you need a internet connection and free space on the HD (if you use something like Backtrack you have a 4GB ramdisk and if it is full, it crashes). And recently my apt system broke, and I could not use apt-get install for anything for 3 months!

[Clucky]

It is definately good to have both of these resources at my hands in case one fails. Thank you btw for the use of regular expression, that was where i was initially getting at with this post. I do enjoy the more simplistic design of xmlstarlet

[tripleee]

The blanket wildcard .* here is definitely dangerous. Try to limit matching with [^<>]* to avoid spanning across tags. There are still many corner cases where this could fail; for example, many XML schemata will allow a line break before a close tag, which will completely break one of the fundamental assumptions of this solution. Altogether, these points illustrate exactly why this approach is problematic.

[Dan Bliss]

Agree that excluding the angle brackets is better.

[Sirojiddin Komolov]

Then how to change the result file again?