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<title>i-found-out-splunk-macros-are-awesome</title>
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<p>Macros are for more than just canned searches.</p>
<p>If you've never seen a macro before, read the doc page here:</p>
<p>https://docs.splunk.com/Documentation/Splunk/9.0.2/Knowledge/Definesearchmacros</p>
<p>What that doc page doesn't tell you is that you need not just stick
any old complicated search in there. If you know how to use
<code>eval</code> you can stick any resulting text anywhere you
want.</p>
<p>Take for example, timestamping your output lookups. Let's say I have
a report that runs every 12 hours that I output to a lookup called
"vpn_users.csv," which contains all users who logged on to VPN in that
time. That report might look something like this:</p>
<pre class="spl"><code>index=syslog sourcetype=vpn
| table _time username
| outputlookup vpn_users.csv</code></pre>
<p>I can easily review that lookup like so:</p>
<p><code>| inputlookup vpn_users.csv</code></p>
<p>My boss might be happy that I'm keeping an eye on things, but what's
the historical picture? How do I know what's a red flag and what isn't?
What I might do is combine all of the days reports into one each day,
and then compare each today. But in the original report logic, this gets
overwritten every 12 hours. You could just append forever, but then
you're not looking at just twelve hours, unless you add a time
constraint to your search. How do I get to a daily report without
interrupting the reports already running?</p>
<p>One way to do it is to create a second combined report unique to that
day, for example 'vpn_users-2022_11_17.csv'. The way you insert that
text is with a macro, defined for the current date. For this particular
format, I can define a macro called <code>today</code> with the
following definition, which just gets the current time and formats
it:</p>
<p><code>strftime(now(), "%Y-%m-%d")</code></p>
<p>Now I literally just stick it to the end of my original search, and
set the lookup file to append, so we <em>add</em> new values rather than
overwrite them:</p>
<pre class="spl"><code>index=syslog sourcetype=vpn
| table _time username
| outputlookup vpn_users.csv
| outputlookup append=t vpn_users-`today`.csv</code></pre>
<p>That's just a super obvious implementation though; there's all sorts
of ways you might want to tag your lookups for ease of access.</p>
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