Error when trying to install app with mysql2 gem

For anybody still experiencing the issue:

When you install openssl via brew, you should get the following message:

Apple has deprecated use of OpenSSL in favor of its own TLS and crypto libraries

Generally there are no consequences of this for you. If you build your own software and it requires this formula, you'll need to add to your build variables:

LDFLAGS: -L/usr/local/opt/openssl/lib
CPPFLAGS: -I/usr/local/opt/openssl/include
PKG_CONFIG_PATH: /usr/local/opt/openssl/lib/pkgconfig

You can set these build flags (for the local application) by running the following:

bundle config --local build.mysql2 "--with-ldflags=-L/usr/local/opt/openssl/lib --with-cppflags=-I/usr/local/opt/openssl/include"

This worked for me.

See bundler's documentation for more information.

The error log says:

ld: library not found for -lssl

So, you need to install libssl:

brew install openssl

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As it was pointed out in comments, there might be a need to export the path to the library.

export LIBRARY_PATH=$LIBRARY_PATH:/usr/local/opt/openssl/lib/