installing mechanize on a mac with an error
<p>I have tried to install mechanize on my Mac but I always get error. I tried all answers given on the site but none worked for me. </p>

<p>I have tried sudo gem install mechanize and I got error below. </p>

<pre><code>Password:
Building native extensions.  This could take a while...
ERROR:  Error installing mechanize:
    ERROR: Failed to build gem native extension.

    current directory: /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.8/ext/nokogiri
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby -r ./siteconf20160703-8312-16oc548.rb extconf.rb
Using pkg-config version 1.1.7
checking if the C compiler accepts ... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using packaged libraries.
Using mini_portile version 2.1.0
checking for iconv.h... yes
checking for gzdopen() in -lz... yes
checking for iconv... yes
************************************************************************
IMPORTANT NOTICE:

Building Nokogiri with a packaged version of libxml2-2.9.4.

Team Nokogiri will keep on doing their best to provide security
updates in a timely manner, but if this is a concern for you and want
to use the system library instead; abort this installation process and
reinstall nokogiri as follows:

    gem install nokogiri -- --use-system-libraries
        [--with-xml2-config=/path/to/xml2-config]
        [--with-xslt-config=/path/to/xslt-config]

If you are using Bundler, tell it to use the option:

    bundle config build.nokogiri --use-system-libraries
    bundle install

Note, however, that nokogiri is not fully compatible with arbitrary
versions of libxml2 provided by OS/package vendors.
************************************************************************
Extracting libxml2-2.9.4.tar.gz into tmp/x86_64-apple-darwin15/ports/libxml2/2.9.4... OK
Running 'configure' for libxml2 2.9.4... OK
Running 'compile' for libxml2 2.9.4... ERROR, review '/Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.8/ext/nokogiri/tmp/x86_64-apple-darwin15/ports/libxml2/2.9.4/compile.log' to see what happened. Last lines are:
========================================================================
    unsigned short* in = (unsigned short*) inb;
                         ^~~~~~~~~~~~~~~~~~~~~
encoding.c:815:27: warning: cast from 'unsigned char *' to 'unsigned short *' increases required alignment from 1 to 2 [-Wcast-align]
    unsigned short* out = (unsigned short*) outb;
                          ^~~~~~~~~~~~~~~~~~~~~~
4 warnings generated.
  CC       error.lo
  CC       parserInternals.lo
  CC       parser.lo
  CC       tree.lo
  CC       hash.lo
  CC       list.lo
  CC       xmlIO.lo
xmlIO.c:1450:52: error: use of undeclared identifier 'LZMA_OK'
    ret =  (__libxml2_xzclose((xzFile) context) == LZMA_OK ) ? 0 : -1;
                                                   ^
1 error generated.
make[2]: *** [xmlIO.lo] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2
========================================================================
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
    --help
    --clean
    --use-system-libraries
    --enable-static
    --disable-static
    --with-zlib-dir
    --without-zlib-dir
    --with-zlib-include
    --without-zlib-include=${zlib-dir}/include
    --with-zlib-lib
    --without-zlib-lib=${zlib-dir}/lib
    --enable-cross-build
    --disable-cross-build
/Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:366:in `block in execute': Failed to complete compile task (RuntimeError)
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:337:in `chdir'
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:337:in `execute'
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:111:in `compile'
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:150:in `cook'
    from extconf.rb:364:in `block (2 levels) in process_recipe'
    from extconf.rb:257:in `block in chdir_for_build'
    from extconf.rb:256:in `chdir'
    from extconf.rb:256:in `chdir_for_build'
    from extconf.rb:363:in `block in process_recipe'
    from extconf.rb:262:in `tap'
    from extconf.rb:262:in `process_recipe'
    from extconf.rb:555:in `&lt;main&gt;'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-15/2.0.0/nokogiri-1.6.8/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.8 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-15/2.0.0/nokogiri-1.6.8/gem_make.out
</code></pre>

<p>I have install Xcode command line and when I do this  </p>

<pre><code>xcode-select -p
</code></pre>

<p>I get /Applications/Xcode.app/Contents/Developer</p>

<p>this is also the error when I try nokogiri
Admins-MBP:~ admin$ sudo gem install nokogiri</p>

<pre><code>Password:
Building native extensions.  This could take a while...
ERROR:  Error installing nokogiri:
    ERROR: Failed to build gem native extension.

    current directory: /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.8/ext/nokogiri
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby -r ./siteconf20160703-27126-1ef91wn.rb extconf.rb
Using pkg-config version 1.1.7
checking if the C compiler accepts ... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using packaged libraries.
Using mini_portile version 2.1.0
checking for iconv.h... yes
checking for gzdopen() in -lz... yes
checking for iconv... yes
************************************************************************
IMPORTANT NOTICE:

Building Nokogiri with a packaged version of libxml2-2.9.4.

Team Nokogiri will keep on doing their best to provide security
updates in a timely manner, but if this is a concern for you and want
to use the system library instead; abort this installation process and
reinstall nokogiri as follows:

    gem install nokogiri -- --use-system-libraries
        [--with-xml2-config=/path/to/xml2-config]
        [--with-xslt-config=/path/to/xslt-config]

If you are using Bundler, tell it to use the option:

    bundle config build.nokogiri --use-system-libraries
    bundle install

Note, however, that nokogiri is not fully compatible with arbitrary
versions of libxml2 provided by OS/package vendors.
************************************************************************
Extracting libxml2-2.9.4.tar.gz into tmp/x86_64-apple-darwin15/ports/libxml2/2.9.4... OK
Running 'configure' for libxml2 2.9.4... OK
Running 'compile' for libxml2 2.9.4... ERROR, review '/Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.8/ext/nokogiri/tmp/x86_64-apple-darwin15/ports/libxml2/2.9.4/compile.log' to see what happened. Last lines are:
========================================================================
  "_libiconv", referenced from:
      _xmlIconvWrapper in libxml2.a(encoding.o)
  "_libiconv_close", referenced from:
      _xmlFindCharEncodingHandler in libxml2.a(encoding.o)
      _xmlCharEncCloseFunc in libxml2.a(encoding.o)
  "_libiconv_open", referenced from:
      _xmlFindCharEncodingHandler in libxml2.a(encoding.o)
  "_lzma_auto_decoder", referenced from:
      _xz_head in libxml2.a(xzlib.o)
  "_lzma_code", referenced from:
      _xz_decomp in libxml2.a(xzlib.o)
  "_lzma_end", referenced from:
      ___libxml2_xzclose in libxml2.a(xzlib.o)
  "_lzma_properties_decode", referenced from:
      _is_format_lzma in libxml2.a(xzlib.o)
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [xmllint] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2
========================================================================
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
    --help
    --clean
    --use-system-libraries
    --enable-static
    --disable-static
    --with-zlib-dir
    --without-zlib-dir
    --with-zlib-include
    --without-zlib-include=${zlib-dir}/include
    --with-zlib-lib
    --without-zlib-lib=${zlib-dir}/lib
    --enable-cross-build
    --disable-cross-build
/Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:366:in `block in execute': Failed to complete compile task (RuntimeError)
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:337:in `chdir'
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:337:in `execute'
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:111:in `compile'
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:150:in `cook'
    from extconf.rb:364:in `block (2 levels) in process_recipe'
    from extconf.rb:257:in `block in chdir_for_build'
    from extconf.rb:256:in `chdir'
    from extconf.rb:256:in `chdir_for_build'
    from extconf.rb:363:in `block in process_recipe'
    from extconf.rb:262:in `tap'
    from extconf.rb:262:in `process_recipe'
    from extconf.rb:555:in `&lt;main&gt;'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-15/2.0.0/nokogiri-1.6.8/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.8 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-15/2.0.0/nokogiri-1.6.8/gem_make.out
</code></pre>

<p>When I use 
Admins-MBP:~ admin$ sudo gem install nokogiri -v '1.6.7.2'</p>

<pre><code>Password:
Fetching: mini_portile2-2.0.0.gem (100%)
Successfully installed mini_portile2-2.0.0
Fetching: nokogiri-1.6.7.2.gem (100%)
Building native extensions.  This could take a while...
ERROR:  Error installing nokogiri:
    ERROR: Failed to build gem native extension.

    current directory: /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/ext/nokogiri
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby -r ./siteconf20160703-32388-1almq9.rb extconf.rb
checking if the C compiler accepts ... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using packaged libraries.
Using mini_portile version 2.0.0
checking for iconv.h... yes
checking for gzdopen() in -lz... yes
checking for iconv... yes
************************************************************************
IMPORTANT NOTICE:

Building Nokogiri with a packaged version of libxml2-2.9.2
with the following patches applied:
    - 0001-Revert-Missing-initialization-for-the-catalog-module.patch
    - 0002-Fix-missing-entities-after-CVE-2014-3660-fix.patch
    - 0003-Stop-parsing-on-entities-boundaries-errors.patch
    - 0004-Cleanup-conditional-section-error-handling.patch
    - 0005-CVE-2015-1819-Enforce-the-reader-to-run-in-constant-.patch
    - 0006-Another-variation-of-overflow-in-Conditional-section.patch
    - 0007-Fix-an-error-in-previous-Conditional-section-patch.patch
    - 0008-CVE-2015-8035-Fix-XZ-compression-support-loop.patch
    - 0009-Updated-config.guess.patch
    - 0010-Fix-parsering-short-unclosed-comment-uninitialized-access.patch
    - 0011-Avoid-extra-processing-of-MarkupDecl-when-EOF.patch
    - 0012-Avoid-processing-entities-after-encoding-conversion-.patch
    - 0013-CVE-2015-7497-Avoid-an-heap-buffer-overflow-in-xmlDi.patch
    - 0014-CVE-2015-5312-Another-entity-expansion-issue.patch
    - 0015-Add-xmlHaltParser-to-stop-the-parser.patch
    - 0016-Detect-incoherency-on-GROW.patch
    - 0017-CVE-2015-7500-Fix-memory-access-error-due-to-incorre.patch
    - 0018-CVE-2015-8242-Buffer-overead-with-HTML-parser-in-pus.patch
    - 0019-Do-not-print-error-context-when-there-is-none.patch
    - 0020-xmlStopParser-reset-errNo.patch
    - 0021-Reuse-xmlHaltParser-where-it-makes-sense.patch

Team Nokogiri will keep on doing their best to provide security
updates in a timely manner, but if this is a concern for you and want
to use the system library instead; abort this installation process and
reinstall nokogiri as follows:

    gem install nokogiri -- --use-system-libraries
        [--with-xml2-config=/path/to/xml2-config]
        [--with-xslt-config=/path/to/xslt-config]

If you are using Bundler, tell it to use the option:

    bundle config build.nokogiri --use-system-libraries
    bundle install

Note, however, that nokogiri is not fully compatible with arbitrary
versions of libxml2 provided by OS/package vendors.
************************************************************************
Extracting libxml2-2.9.2.tar.gz into tmp/x86_64-apple-darwin15/ports/libxml2/2.9.2... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0001-Revert-Missing-initialization-for-the-catalog-module.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0002-Fix-missing-entities-after-CVE-2014-3660-fix.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0003-Stop-parsing-on-entities-boundaries-errors.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0004-Cleanup-conditional-section-error-handling.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0005-CVE-2015-1819-Enforce-the-reader-to-run-in-constant-.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0006-Another-variation-of-overflow-in-Conditional-section.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0007-Fix-an-error-in-previous-Conditional-section-patch.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0008-CVE-2015-8035-Fix-XZ-compression-support-loop.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0009-Updated-config.guess.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0010-Fix-parsering-short-unclosed-comment-uninitialized-access.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0011-Avoid-extra-processing-of-MarkupDecl-when-EOF.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0012-Avoid-processing-entities-after-encoding-conversion-.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0013-CVE-2015-7497-Avoid-an-heap-buffer-overflow-in-xmlDi.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0014-CVE-2015-5312-Another-entity-expansion-issue.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0015-Add-xmlHaltParser-to-stop-the-parser.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0016-Detect-incoherency-on-GROW.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0017-CVE-2015-7500-Fix-memory-access-error-due-to-incorre.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0018-CVE-2015-8242-Buffer-overead-with-HTML-parser-in-pus.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0019-Do-not-print-error-context-when-there-is-none.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0020-xmlStopParser-reset-errNo.patch... OK
Running git apply with /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/patches/libxml2/0021-Reuse-xmlHaltParser-where-it-makes-sense.patch... OK
Running 'configure' for libxml2 2.9.2... OK
Running 'compile' for libxml2 2.9.2... ERROR, review '/Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2/ext/nokogiri/tmp/x86_64-apple-darwin15/ports/libxml2/2.9.2/compile.log' to see what happened. Last lines are:
========================================================================
  "_gzwrite", referenced from:
      _xmlGzfileWrite in libxml2.a(xmlIO.o)
  "_inflate", referenced from:
      _xmlNanoHTTPRead in libxml2.a(nanohttp.o)
  "_inflateEnd", referenced from:
      _xmlNanoHTTPFreeCtxt in libxml2.a(nanohttp.o)
  "_inflateInit2_", referenced from:
      _xmlNanoHTTPScanAnswer in libxml2.a(nanohttp.o)
  "_libiconv", referenced from:
      _xmlIconvWrapper in libxml2.a(encoding.o)
  "_libiconv_close", referenced from:
      _xmlFindCharEncodingHandler in libxml2.a(encoding.o)
      _xmlCharEncCloseFunc in libxml2.a(encoding.o)
  "_libiconv_open", referenced from:
      _xmlFindCharEncodingHandler in libxml2.a(encoding.o)
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [xmllint] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2
========================================================================
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
    --help
    --clean
    --use-system-libraries
    --enable-static
    --disable-static
    --with-zlib-dir
    --without-zlib-dir
    --with-zlib-include
    --without-zlib-include=${zlib-dir}/include
    --with-zlib-lib
    --without-zlib-lib=${zlib-dir}/lib
    --enable-cross-build
    --disable-cross-build
/Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:366:in `block in execute': Failed to complete compile task (RuntimeError)
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:337:in `chdir'
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:337:in `execute'
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:111:in `compile'
    from /Library/Ruby/Gems/2.0.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:150:in `cook'
    from extconf.rb:289:in `block (2 levels) in process_recipe'
    from extconf.rb:182:in `block in chdir_for_build'
    from extconf.rb:181:in `chdir'
    from extconf.rb:181:in `chdir_for_build'
    from extconf.rb:288:in `block in process_recipe'
    from extconf.rb:187:in `tap'
    from extconf.rb:187:in `process_recipe'
    from extconf.rb:478:in `&lt;main&gt;'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-15/2.0.0/nokogiri-1.6.7.2/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.7.2 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-15/2.0.0/nokogiri-1.6.7.2/gem_make.out
</code></pre>

<p>another error </p>

<pre><code>Admins-MBP:~ admin$ sudo gem install nokogiri -- --use-system-libraries --with-xslt-dir=/usr/local/opt/libxslt --with-iconv-dir=/usr/local/opt/libiconv --with-xml2-dir=/usr/local/opt/libxml2 --with-xml2-config=/usr/local/opt/libxml2/bin/xml2-config --with-xml2-include=/usr/local/opt/libxml2/include/libxml2 --with-xslt-config=/usr/local/opt/libxslt/bin/xslt-config
Password:
Building native extensions with: '--use-system-libraries --with-xslt-dir=/usr/local/opt/libxslt --with-iconv-dir=/usr/local/opt/libiconv --with-xml2-dir=/usr/local/opt/libxml2 --with-xml2-config=/usr/local/opt/libxml2/bin/xml2-config --with-xml2-include=/usr/local/opt/libxml2/include/libxml2 --with-xslt-config=/usr/local/opt/libxslt/bin/xslt-config'
This could take a while...
ERROR:  Error installing nokogiri:
    ERROR: Failed to build gem native extension.

    current directory: /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.8/ext/nokogiri
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby -r ./siteconf20160703-514-1ycei3y.rb extconf.rb --use-system-libraries --with-xslt-dir=/usr/local/opt/libxslt --with-iconv-dir=/usr/local/opt/libiconv --with-xml2-dir=/usr/local/opt/libxml2 --with-xml2-config=/usr/local/opt/libxml2/bin/xml2-config --with-xml2-include=/usr/local/opt/libxml2/include/libxml2 --with-xslt-config=/usr/local/opt/libxslt/bin/xslt-config
Using pkg-config version 1.1.7
checking if the C compiler accepts ... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using system libraries.
checking for libexslt... no
ERROR: cannot discover where libxml2 is located on your system. please make sure `pkg-config` is installed.
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
    --help
    --clean
    --use-system-libraries
    --with-zlib-dir
    --without-zlib-dir
    --with-zlib-include
    --without-zlib-include=${zlib-dir}/include
    --with-zlib-lib
    --without-zlib-lib=${zlib-dir}/lib
    --with-xml2-dir
    --with-xml2-include=${xml2-dir}/include
    --with-xml2-lib
    --without-xml2-lib=${xml2-dir}/lib
    --with-xslt-dir
    --with-xslt-include
    --without-xslt-include=${xslt-dir}/include
    --with-xslt-lib
    --without-xslt-lib=${xslt-dir}/lib
    --with-exslt-dir
    --without-exslt-dir
    --with-exslt-include
    --without-exslt-include=${exslt-dir}/include
    --with-exslt-lib
    --without-exslt-lib=${exslt-dir}/lib
    --with-libexslt-config
    --without-libexslt-config
    --with-pkg-config
    --without-pkg-config
    --with-pkg-config
    --without-pkg-config
    --with-override-variables
    --without-override-variables

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-15/2.0.0/nokogiri-1.6.8/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.8 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-15/2.0.0/nokogiri-1.6.8/gem_make.out
</code></pre>