El Capitanで新規でawscliをインストールする｡
OSXのバージョンはこんな感じ｡

$ sw_vers
ProductName:	Mac OS X
ProductVersion:	10.11.6
BuildVersion:	15G31

pythonはデフォルトでインストールされている｡

$ python --version
Python 2.7.10

pipはデフォルトで入っていないので個別に導入｡

$ sudo easy_install pip

Searching for pip
Reading https://pypi.python.org/simple/pip/
Best match: pip 8.1.2
Downloading https://pypi.python.org/packages/e7/a8/7556133689add8d1a54c0b14aeff0acb03c64707ce100ecd53934da1aa13/pip-8.1.2.tar.gz#md5=87083c0b9867963b29f7aba3613e8f4a
Processing pip-8.1.2.tar.gz
Writing /tmp/easy_install-8MACl7/pip-8.1.2/setup.cfg
Running pip-8.1.2/setup.py -q bdist_egg --dist-dir /tmp/easy_install-8MACl7/pip-8.1.2/egg-dist-tmp-735OuD
warning: no previously-included files found matching '.coveragerc'
warning: no previously-included files found matching '.mailmap'
warning: no previously-included files found matching '.travis.yml'
warning: no previously-included files found matching '.landscape.yml'
warning: no previously-included files found matching 'pip/_vendor/Makefile'
warning: no previously-included files found matching 'tox.ini'
warning: no previously-included files found matching 'dev-requirements.txt'
warning: no previously-included files found matching 'appveyor.yml'
no previously-included directories found matching '.github'
no previously-included directories found matching '.travis'
no previously-included directories found matching 'docs/_build'
no previously-included directories found matching 'contrib'
no previously-included directories found matching 'tasks'
no previously-included directories found matching 'tests'
Adding pip 8.1.2 to easy-install.pth file
Installing pip script to /usr/local/bin
Installing pip2.7 script to /usr/local/bin
Installing pip2 script to /usr/local/bin

Installed /Library/Python/2.7/site-packages/pip-8.1.2-py2.7.egg
Processing dependencies for pip
Finished processing dependencies for pip

ここから以下を参考にawscliをインストール｡ありがとうございます｡
OSX El Capitanでawscliのインストールに失敗する場合の対処方法

$ sudo -H pip install awscli --upgrade --ignore-installed six

Collecting awscli
  Downloading awscli-1.10.56-py2.py3-none-any.whl (986kB)
    100% |████████████████████████████████| 993kB 1.1MB/s 
Collecting six
  Downloading six-1.10.0-py2.py3-none-any.whl
Collecting s3transfer<0.2.0,>=0.1.0 (from awscli)
  Downloading s3transfer-0.1.1-py2.py3-none-any.whl (49kB)
    100% |████████████████████████████████| 51kB 6.5MB/s 
Collecting docutils>=0.10 (from awscli)
  Downloading docutils-0.12.tar.gz (1.6MB)
    100% |████████████████████████████████| 1.6MB 590kB/s 
Collecting botocore==1.4.46 (from awscli)
  Downloading botocore-1.4.46-py2.py3-none-any.whl (2.5MB)
    100% |████████████████████████████████| 2.5MB 391kB/s 
Collecting rsa<=3.5.0,>=3.1.2 (from awscli)
  Downloading rsa-3.4.2-py2.py3-none-any.whl (46kB)
    100% |████████████████████████████████| 51kB 6.1MB/s 
Collecting colorama<=0.3.7,>=0.2.5 (from awscli)
  Downloading colorama-0.3.7-py2.py3-none-any.whl
Collecting futures<4.0.0,>=2.2.0; python_version == "2.6" or python_version == "2.7" (from s3transfer<0.2.0,>=0.1.0->awscli)
  Downloading futures-3.0.5-py2-none-any.whl
Collecting python-dateutil<3.0.0,>=2.1 (from botocore==1.4.46->awscli)
  Downloading python_dateutil-2.5.3-py2.py3-none-any.whl (201kB)
    100% |████████████████████████████████| 204kB 1.4MB/s 
Collecting jmespath<1.0.0,>=0.7.1 (from botocore==1.4.46->awscli)
  Downloading jmespath-0.9.0-py2.py3-none-any.whl
Collecting pyasn1>=0.1.3 (from rsa<=3.5.0,>=3.1.2->awscli)
  Downloading pyasn1-0.1.9-py2.py3-none-any.whl
Installing collected packages: futures, six, python-dateutil, docutils, jmespath, botocore, s3transfer, pyasn1, rsa, colorama, awscli
  Running setup.py install for docutils ... done
Successfully installed awscli-1.10.56 botocore-1.4.46 colorama-0.3.7 docutils-0.12 futures-3.0.5 jmespath-0.9.0 pyasn1-0.1.9 python-dateutil-1.5 rsa-3.4.2 s3transfer-0.1.1 six-1.4.1

$ aws --version
aws-cli/1.10.56 Python/2.7.10 Darwin/15.6.0 botocore/1.4.46

できた｡