Searching Delimited Log Files (alternatively, sed is black magic)

Table of Contents

The problem

Ever find yourself looking through log files that look like this:

-----------
Just a regular log entry
-----------
Another log entry, now
spanning multiple lines
-----------
And all seperated by a series
of dashes.  Though, really, it
could be any sort of seperator.
-----------
Also, we don't necessarily end
with an entry seperator.

Ever wanted to grep for the entry that contains a given piece of text, but wanted to see the full entry? That is, if you wanted to find the entry that had the word "necessarily," but wanted to see the full entry:

-----------
Also, we don't necessarily end
with an entry seperator.

Odds are there are plenty of tools that do this of which I am not familiar. Hopefully someone can find a way to let me know about them.

In the meantime, however, here is a bit of sed black magic that can accomplish the goal. I should say that this does have a major benefit, in that sed is installed everywhere.

Black Magic

Our goal is fairly simple, we want to invoke sed such that it does not print out the entire file. We want to hold all lines that are not seperators. And then, at a seperator or the end of the file, we want to check all of the lines that we have held for our search pattern, print if found, otherwise delete and continue.

sed -n -e "/^----/!H; /^----/ b test; $ b test; d; : test { x; /necessarily/p }"

Simply pass the file or the contents of the file to sed however you want and out come your results.

Author: Josh Berry

Created: 2016-11-19 Sat 17:18

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