Fix "library not loaded" error with Brew • gsempe

Ruby, PHP and a lot other languages rely on system libraries to provide some features in their own ecosystems. It times to times leads to this kind of error

Library not loaded: /usr/local/lib/libjpeg.8.dylib

A large majority of developers on OSX use Brew package manager to install the libraries they need. On the above library loading error, the immediate reaction is so to brew install it

brew install libjpeg
Warning: jpeg 9c is already installed and up-to-date
To reinstall 9c, run `brew reinstall jpeg`

In most of the cases, you don’t have the library missing installed and you can continue with you main task. In some cases, like mine, you already have it installed and you still have your problem.

The solution can be to switch the libjpeg version installed by Brew. First, retrieve the formulae’s info

brew info libjpeg
jpeg: stable 9c (bottled)
Image manipulation library
http://www.ijg.org
/usr/local/Cellar/jpeg/8d (19 files, 731.2KB)
  Poured from bottle on 2014-10-17 at 21:30:18
/usr/local/Cellar/jpeg/9b (20 files, 724KB)
  Poured from bottle on 2018-02-20 at 17:37:34
/usr/local/Cellar/jpeg/9c (21 files, 724.6KB) *
  Poured from bottle on 2018-06-12 at 14:24:01
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/jpeg.rb

And finally, switch to the version that you need. I was needed version 8, so I’m interested in 8d version

brew switch libjpeg 8d
Cleaning /usr/local/Cellar/jpeg/8d
Cleaning /usr/local/Cellar/jpeg/9b
Cleaning /usr/local/Cellar/jpeg/9c
17 links created for /usr/local/Cellar/jpeg/8d

It fixed the error in my case. This quick tip will help me to go faster next time.
Hopefully, it’ll help you too.