在mac上安装openssl

 brew install openssl
显示如下：

Updating Homebrew...
==> Downloading https://homebrew.bintray.com/bottles/openssl-1.0.2l.el_capitan.b
######################################################################## 100.0%
==> Pouring openssl-1.0.2l.el_capitan.bottle.tar.gz
==> Using the sandbox
==> Caveats
A CA file has been bootstrapped using certificates from the SystemRoots
keychain. To add additional certificates (e.g. the certificates added in
the System keychain), place .pem files in
  /usr/local/etc/openssl/certs

and run
  /usr/local/opt/openssl/bin/c_rehash

This formula is keg-only, which means it was not symlinked into /usr/local,
because Apple has deprecated use of OpenSSL in favor of its own TLS and crypto libraries.

If you need to have this software first in your PATH run:
  echo 'export PATH="/usr/local/opt/openssl/bin:$PATH"' >> ~/.bash_profile

For compilers to find this software you may need to set:
    LDFLAGS:  -L/usr/local/opt/openssl/lib
    CPPFLAGS: -I/usr/local/opt/openssl/include
For pkg-config to find this software you may need to set:
    PKG_CONFIG_PATH: /usr/local/opt/openssl/lib/pkgconfig

==> Summary
🍺  /usr/local/Cellar/openssl/1.0.2l: 1,709 files, 12.1MB

----------------
运行brew install openssl显示：
...
To add additional certificates, place .pem files in
  /usr/local/etc/openssl/certs

and run
  /usr/local/opt/openssl/bin/c_rehash

This formula is keg-only, which means it was not symlinked into /usr/local.

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

==> Summary
🍺  /usr/local/Cellar/openssl/1.0.2d_1
-----------
即：在编译某个程序的源码时，在./configure那一步，要加上参数如下：
./configure  LDFLAGS=-L/usr/local/opt/openssl/lib CPPFLAGS=-I/usr/local/opt/openssl/include

然后make

实例见此：http://briteming.blogspot.com/2016/06/sockstunnel.html

－－－－－－－－－

运行brew reinstall openssl显示：
...

A CA file has been bootstrapped using certificates from the system

keychain. To add additional certificates, place .pem files in

  /usr/local/etc/openssl@1.1/certs

and run

  /usr/local/opt/openssl@1.1/bin/c_rehash

openssl@1.1 is keg-only, which means it was not symlinked into /usr/local,

because macOS provides LibreSSL.

If you need to have openssl@1.1 first in your PATH run:

  echo 'export PATH="/usr/local/opt/openssl@1.1/bin:$PATH"' >> ~/.bash_profile

For compilers to find openssl@1.1 you may need to set:

  export LDFLAGS="-L/usr/local/opt/openssl@1.1/lib"

  export CPPFLAGS="-I/usr/local/opt/openssl@1.1/include"

For pkg-config to find openssl@1.1 you may need to set:

  export PKG_CONFIG_PATH="/usr/local/opt/openssl@1.1/lib/pkgconfig"

==> Summary

🍺  /usr/local/Cellar/openssl@1.1/1.1.1g: 8,052 files, 18.4MB, built in 11 minutes 1 second.

--------------------

类似的：

yudeMacBook-Air:~ brite$ brew install libffi

Warning: You are using OS X 10.11.

We do not provide support for this pre-release version.

You may encounter build failures or other breakage.

==> Downloading https://mirrors.kernel.org/sources.redhat.com/libffi/libffi-3.0.

curl: (28) Resolving timed out after 5529 milliseconds

Trying a mirror...

==> Downloading ftp://sourceware.org/pub/libffi/libffi-3.0.13.tar.gz

######################################################################## 100.0%

==> ./configure --prefix=/usr/local/Cellar/libffi/3.0.13

==> make install

==> Caveats

This formula is keg-only, which means it was not symlinked into /usr/local.

Some formulae require a newer version of libffi.

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/libffi/lib

==> Summary

🍺  /usr/local/Cellar/libffi/3.0.13: 14 files, 400K, built in 46 seconds

yudeMacBook-Air:~ brite$

即：在编译某个程序的源码时，在make那一步，要加上参数如下：

make  LDFLAGS=-L/usr/local/opt/libffi/lib

又一例子：http://briteming.blogspot.com/2018/04/sshaskellshadowsocks-haskell.html

相关帖子：
http://briteming.blogspot.com/2016/06/os-x-1011openssl.html