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+<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>Aggregating data with AWK</nadpis>
+ <perex>counting records and computing sum or appending new records</perex>
+ <m:pořadí-příkladu>02600</m:pořadí-příkladu>
+
+ <text xmlns="http://www.w3.org/1999/xhtml">
+
+ <p>
+ We have filtered records, modified attribute values, added and removed attributes, dropped a relation…
+ and there is one more operation that we can do with AWK: <code>INSERT</code> resp. appending or preppending additional records to the relation
+ – and we can also completely replace the record set by skipping the original records.
+ </p>
+
+ <h2>Adding records</h2>
+
+ <p>
+ Using options <code>--before-records</code> and <code>--after-records</code> we can pass additional AWK code that will be executed – once for given relation.
+ The <code>record()</code> function will then generate an additional record (can be called multiple times and generate more records):
+ </p>
+
+ <m:pre jazyk="bash"><![CDATA[awkCode='
+ scheme = "";
+ device = "/dev/vg1/volume123";
+ mount_point = "/mnt/v123";
+ type = "btrfs";
+ options = "relatime";
+ dump = 0;
+ pass = 2;
+
+ record();
+';
+
+relpipe-in-fstab \
+ | relpipe-tr-awk \
+ --relation '.*' \
+ --for-each '1' \
+ --after-records "$awkCode" \
+ | relpipe-out-tabular]]></m:pre>
+
+ <p>Which will <code>INSERT</code> one new record:</p>
+
+ <pre><![CDATA[fstab:
+ ╭─────────────────┬──────────────────────────────────────┬──────────────────────┬───────────────┬───────────────────────────────────────┬────────────────┬────────────────╮
+ │ scheme (string) │ device (string) │ mount_point (string) │ type (string) │ options (string) │ dump (integer) │ pass (integer) │
+ ├─────────────────┼──────────────────────────────────────┼──────────────────────┼───────────────┼───────────────────────────────────────┼────────────────┼────────────────┤
+ │ UUID │ 29758270-fd25-4a6c-a7bb-9a18302816af │ / │ ext4 │ relatime,user_xattr,errors=remount-ro │ 0 │ 1 │
+ │ │ /dev/sr0 │ /media/cdrom0 │ udf,iso9660 │ user,noauto │ 0 │ 0 │
+ │ │ /dev/sde │ /mnt/data │ ext4 │ relatime,user_xattr,errors=remount-ro │ 0 │ 2 │
+ │ UUID │ a2b5f230-a795-4f6f-a39b-9b57686c86d5 │ /home │ btrfs │ relatime │ 0 │ 2 │
+ │ │ /dev/mapper/sdf_crypt │ /mnt/private │ xfs │ relatime │ 0 │ 2 │
+ │ │ /dev/vg1/volume123 │ /mnt/v123 │ btrfs │ relatime │ 0 │ 2 │
+ ╰─────────────────┴──────────────────────────────────────┴──────────────────────┴───────────────┴───────────────────────────────────────┴────────────────┴────────────────╯
+Record count: 6]]></pre>
+
+ <h2>Counting and summarizing values</h2>
+
+ <p>We can also compute some statistics like <code>COUNT()</code> and <code>SUM()</code>:</p>
+
+ <m:pre jazyk="bash"><![CDATA[find -print0 | relpipe-in-filesystem \
+ | relpipe-tr-awk \
+ --relation '.*' \
+ --before-records 'count = 0; total_size = 0;' \
+ --for-each '{ count++; total_size += size; }' \
+ --after-records 'record();' \
+ --output-attribute count integer \
+ --output-attribute total_size integer \
+ | relpipe-out-tabular]]></m:pre>
+
+ <p>and get result:</p>
+
+ <pre><![CDATA[filesystem:
+ ╭─────────────────┬──────────────────────╮
+ │ count (integer) │ total_size (integer) │
+ ├─────────────────┼──────────────────────┤
+ │ 9 │ 818747 │
+ ╰─────────────────┴──────────────────────╯
+Record count: 1]]></pre>
+
+ <p>Where the <code>total_size</code> is the same as will <code>du</code> compute:</p>
+
+ <pre>find . -type f -print0 | du -b -c --files0-from=-</pre>
+
+ <p>Analogously we can compute minimum, maximum etc. using AWK transformation.</p>
+
+ </text>
+
+</stránka>