JSON pattern matching with sed, perl and regular expressions
Imagine having a tool that can automatically detect if you are using JPA and Hibernate properly. Hypersistence Optimizer is that tool!
Why VIM?
Sooner or later there comes the day when your easy-to-use IDE becomes useless for handling huge files. There aren’t many editors capable of working with very large files, like production logs for instance.
I’ve recently had to analyze a 100 MB one-line JSON file and once more VIM saved the day. VIM, like many other Unix utilities, is both tough and brilliant.
Git interactive rebase uses VIM by default, and if you’re still not convinced, maybe this great article will make you change your mind.
Let’s see how easily you can pretty print a JSON file with VIM. First, we will download a one-line JSON file from Reddit.
$ wget http://www.reddit.com/r/programming.json --2014-01-24 12:21:04-- http://www.reddit.com/r/programming.json Resolving www.reddit.com (www.reddit.com)... 77.232.217.122, 77.232.217.113 Connecting to www.reddit.com (www.reddit.com)|77.232.217.122|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 28733 (28K) [application/json] Saving to: `programming.json' 100%[======================================>] 28,733 --.-K/s in 0.03s 2014-01-24 12:21:04 (1021 KB/s) - `programming.json' saved [28733/28733]
This is how it looks like:
Pretty printing
Python comes along with most Unix distributions, so running the following VIM command manages to do the trick:
%!python -m json.tool
Let’s save the pretty printed JSON file and put other Unix tools to work.
:w programming_pretty.json
Matching time
Let’s say we want to extract all “domain” related values:
"domain": "mameworld.info"
Sed to the rescue
$ sed -nr 's/^.*"domain":\s*"(.*?)".*$/\1/p' <programming_pretty.json | sort -u blog.safaribooksonline.com chadfowler.com cyrille.rossant.net dot.kde.org evanmiller.org fabiensanglard.net galileo.phys.virginia.edu github.com halffull.org ibuildings.nl jaxenter.com jobtipsforgeeks.com kilncode.com libtins.github.io mameworld.info miguelcamba.com minuum.com notes.tweakblogs.net perfect-pentago.net periscope.io reuters.com tech.blog.box.com tmm1.net vocalbit.com youtube.com
Multi-line matching
Sed is line oriented, and while it offers multi-line support, it’s no match for Perl. Let’s say I want to match all authors in the following JSON pattern:
"data": {
"author": "justrelaxnow",
}
This is how I do it:
$ perl -0777 -n -e 'print "$2\n" while (m/("data":\s*\{.*?"author":\s*"(.*?)"[,|\s*\}].*?\},)/sgmp)' programming_pretty.json | sort -u
AmericanXer0
azth
bionicseraph
bit_shiftr
charles_the_hard
Gexos
jakubgarfield
johnwaterwood
joukoo
justrelaxnow
Kingvash
krets
mariuz
mopatches
nyphrex
pseudomind
rluecke3
sltkr
solidus-flux
steveklabnik1
sumstozero
swizec
vocalbit
Wolfspaw
Conclusion
Unix tools are old school, some of those being written forty years ago. The learning curve might be steep, but learning them is a great investment. A great software library stands the test of time and Unix tools are a good reminder that tough jobs call for tough tools.
Download free ebook sample
If you subscribe to my newsletter, you'll get:
- A free sample of my Video Course about running Integration tests at warp-speed using Docker and tmpfs
- 3 chapters from my book, High-Performance Java Persistence,
- a 10% discount coupon for my book.
