Using sed with a newline in a regex

Question

I'm bashing my head against the wall with this one. How do I do a regex replacement with sed on text that contains a newline?

I need to replace the value of the "version" XML element shown below. There are multiple version elements so I want to replace the one that comes after the "name" element.

<name>MyName</name>
<version>old</version>

Here's my command:

sed -i -E "s@(\s*<name>$NAME</name>\n\s*<version>)$VERSION_OLD(</version>)@\1$VERSION_NEW\2@g" $myfile.txt

Now as far as I know there is a way to make sed work with a newline character, but I can't figure it out. I've already used sed in my script so ideally I'd prefer to re-use it instead of say perl.

The solution is to use a tool designed for working with XML, not sed! — Tom Fenech, Nov 11 '15 at 17:07
Is there a decent standard Bash tool for parsing and manipulating XML? This is part of a larger Bash script... — Boon, Nov 11 '15 at 17:09
Regarding parsing XML with regex, see [the famous post](http://stackoverflow.com/a/1732454/675568). — Tom Zych, Nov 11 '15 at 17:21
I'm not aware of any tool that would provide you with a one-line solution - perhaps it's worth looking at a solution in a language such as perl or python. Alternatively there's always good ol' XSLT :) — Tom Fenech, Nov 11 '15 at 17:26

score 3 · Answer 1 · edited Nov 11 '15 at 19:43

3

When you see your name element, you will need to use the N command to read the next line:

file:

<bar>MyName</bar>
<version>old</version>
<name>MyName</name>
<version>old</version>
<foo>MyName</foo>
<version>old</version>

With GNU sed:

sed '/<name>/{N;s/old/newer/}' file

Output:

<bar>MyName</bar>
<version>old</version>
<name>MyName</name>
<version>new</version>
<foo>MyName</foo>
<version>old</version>

edited Nov 11 '15 at 19:43

Toby Speight

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answered Nov 11 '15 at 19:13

Cyrus

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If the `name` element might also contain `old`, you'll want something a bit more robust, such as `N;P;s/.*\n//;s/old/newer/` – Toby Speight Nov 11 '15 at 19:49
Thank you. Or replace in my version `N` by `n`. – Cyrus Nov 11 '15 at 20:26

score 0 · Answer 2 · answered Nov 12 '15 at 08:33

If you're using GNU sed, you can use its extended addressing syntax:

sed '/<name>/,+1{/<version>/s/old/newer/}' file

Breaking this down, it says: for a line matching <name> and the following line (+1), then if the line matches <version>, substitute old with newer.

I'm assuming here that your file is generated, and will always have the name and version elements each on a single line, and adjacent. If you need to handle more free-form XML, then you should really consider an XPath-based tool rather than sed.

Using sed with a newline in a regex

2 Answers2