yaml-cpp: error: 'unistd.h' file not found

[mikemadden42@…]

On OS X El Capitan, I cannot build / install yaml-cpp:

mjmadden@aslan: ~
 $ sw_vers                                                           [14:13:00]
ProductName:	Mac OS X
ProductVersion:	10.11
BuildVersion:	15A284

mjmadden@aslan: ~
 $ port version                                                      [14:13:23]
Version: 2.3.4

mjmadden@aslan: ~
 $ sudo port clean yaml-cpp                                          [14:13:20]
--->  Cleaning yaml-cpp

mjmadden@aslan: ~
 $ sudo port install yaml-cpp                                        [14:13:39]
--->  Computing dependencies for yaml-cpp
--->  Fetching archive for yaml-cpp
--->  Attempting to fetch yaml-cpp-0.5.1_0.darwin_15.x86_64.tbz2 from http://packages.macports.org/yaml-cpp
--->  Attempting to fetch yaml-cpp-0.5.1_0.darwin_15.x86_64.tbz2 from http://lil.fr.packages.macports.org/yaml-cpp
--->  Attempting to fetch yaml-cpp-0.5.1_0.darwin_15.x86_64.tbz2 from http://nue.de.packages.macports.org/macports/packages/yaml-cpp
--->  Fetching distfiles for yaml-cpp
--->  Verifying checksums for yaml-cpp
--->  Extracting yaml-cpp
--->  Applying patches to yaml-cpp
--->  Configuring yaml-cpp
--->  Building yaml-cpp
Error: org.macports.build for port yaml-cpp returned: command execution failed
Please see the log file for port yaml-cpp for details:
    /opt/local/var/macports/logs/_opt_local_var_macports_sources_www.macports.org_files_ports_devel_yaml-cpp/yaml-cpp/main.log
To report a bug, follow the instructions in the guide:
    http://guide.macports.org/#project.tickets
Error: Processing of port yaml-cpp failed

[mikemadden42@…]

log file for port yaml-cpp

[ryandesign (Ryan Carsten Schmidt)]

The error in the log says:

error: 'unistd.h' file not found

Are you sure you installed both Xcode 7 and the Xcode command line tools? unistd.h should be part of the command line tools. To install them, run "xcode-select --install".

[mikemadden42@…]

Please close this ticket. Running the following before installing the port fixed the issue:

xcode-select --install