2017-08-11 XML and the Command Line

In a recent thread on Mastodon I mentioned some command line tools for working with HTML. Basically: convert it to XML and use the XML command line tools xmllint and xmlstarlet (see XMLStarlet, the xmllint man page and the libxml page).

In order to download from the web we will use curl (see the curl homepage) and in order to display HTML we use w3m with the -T text/html option (see the w3m homepage).

The first thing to know is that xmllint can parse HTML using the --html option and evaluate XPath using the --xpath option.

curl --silent https://alexschroeder.ch/ | xmllint --html --xpath '//h1/text()' -

The result is “Moved Permanently” (because you’re being redirected to the wiki).

If you want to explore stuff interactively, xmllint comes with a built in shell that treats the DOM as a directory tree!

curl --silent https://alexschroeder.ch/wiki > a.html
xmllint --html --shell a.html

You can now use commands such as these:

cd html/body/div/h1
cat a/text()
grep Diary
du /html/body/div[1]

It’s amazing!

If you want to edit HTML you need a different tool, though. This fetches a page, converts to XML, deletes the H1, converts back to HTML, and displays it:

curl --silent https://alexschroeder.ch/ \
| xmllint --html --dropdtd - \
| xmlstarlet ed --delete //h1 \
| xmllint --htmlout - \
| w3m -T text/html

We need to drop the DTD or xmlstarlet will complain.

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