<stránka
xmlns="https://trac.frantovo.cz/xml-web-generator/wiki/xmlns/strana"
xmlns:m="https://trac.frantovo.cz/xml-web-generator/wiki/xmlns/makro">
<nadpis>Reading extended attributes using relpipe-in-filesystem</nadpis>
<perex>accessing xattr of given files e.g. xdg.origin.url</perex>
<m:pořadí-příkladu>01300</m:pořadí-příkladu>
<text xmlns="http://www.w3.org/1999/xhtml">
<p>
Extended attributes (xattr) are additional <em>key=value</em> pairs that can be attached to our files.
They are not stored inside the files, but on the filesystem.
Thus they are independent of particular file format (which might not support metadata)
and we can use them e.g. for tagging, cataloguing or adding some notes to our files.
Some tools like GNU Wget use extended attributes to store metadata like the original URL from which the file was downloaded.
</p>
<m:pre jazyk="bash"><![CDATA[wget --recursive --level=1 https://relational-pipes.globalcode.info/
find -type f -printf '%P\0' \
| relpipe-in-filesystem --file path --file size --xattr xdg.origin.url \
| relpipe-out-tabular
]]></m:pre>
<p>And now we know, where the files on our disk came from:</p>
<pre><![CDATA[filesystem:
╭───────────────────────────┬────────────────┬────────────────────────────────────────────────────────────────────╮
│ path (string) │ size (integer) │ xdg.origin.url (string) │
├───────────────────────────┼────────────────┼────────────────────────────────────────────────────────────────────┤
│ index.html │ 12159 │ https://relational-pipes.globalcode.info/v_0/ │
│ v_0/atom.xml │ 4613 │ https://relational-pipes.globalcode.info/v_0/atom.xml │
│ v_0/rss.xml │ 4926 │ https://relational-pipes.globalcode.info/v_0/rss.xml │
│ v_0/js/skript.js │ 2126 │ https://relational-pipes.globalcode.info/v_0/js/skript.js │
│ v_0/css/styl.css │ 2988 │ https://relational-pipes.globalcode.info/v_0/css/styl.css │
│ v_0/css/relpipe.css │ 1095 │ https://relational-pipes.globalcode.info/v_0/css/relpipe.css │
│ v_0/css/syntaxe.css │ 3584 │ https://relational-pipes.globalcode.info/v_0/css/syntaxe.css │
│ v_0/index.xhtml │ 12159 │ https://relational-pipes.globalcode.info/v_0/index.xhtml │
│ v_0/grafika/logo.png │ 3298 │ https://relational-pipes.globalcode.info/v_0/grafika/logo.png │
│ v_0/principles.xhtml │ 17171 │ https://relational-pipes.globalcode.info/v_0/principles.xhtml │
│ v_0/roadmap.xhtml │ 11097 │ https://relational-pipes.globalcode.info/v_0/roadmap.xhtml │
│ v_0/faq.xhtml │ 11080 │ https://relational-pipes.globalcode.info/v_0/faq.xhtml │
│ v_0/specification.xhtml │ 12983 │ https://relational-pipes.globalcode.info/v_0/specification.xhtml │
│ v_0/implementation.xhtml │ 10810 │ https://relational-pipes.globalcode.info/v_0/implementation.xhtml │
│ v_0/examples.xhtml │ 76958 │ https://relational-pipes.globalcode.info/v_0/examples.xhtml │
│ v_0/license.xhtml │ 65580 │ https://relational-pipes.globalcode.info/v_0/license.xhtml │
│ v_0/screenshots.xhtml │ 5708 │ https://relational-pipes.globalcode.info/v_0/screenshots.xhtml │
│ v_0/download.xhtml │ 5204 │ https://relational-pipes.globalcode.info/v_0/download.xhtml │
│ v_0/contact.xhtml │ 4940 │ https://relational-pipes.globalcode.info/v_0/contact.xhtml │
│ v_0/classic-example.xhtml │ 9539 │ https://relational-pipes.globalcode.info/v_0/classic-example.xhtml │
╰───────────────────────────┴────────────────┴────────────────────────────────────────────────────────────────────╯
Record count: 20]]></pre>
<p>
If we like the BeOS/Haiku style, we can create empty files with some attributes attached and use our filesystem as a simple database
and query it using relational tools.
It will lack indexing, but for basic scenarios like <em>address book</em> it will be fast enough
and we can feel a bit of BeOS/Haiku atmosphere in our contemporary GNU/Linux systems.
But be careful with that because some editors delete and recreate files while saving them, which destroys the xattrs.
Tools like <code>rsync</code> or <code>tar</code> with <code>--xattrs</code> option will backup our attributes securely.
</p>
</text>
</stránka>