Scanning binaries for linking errors when installing cairo on Mac

[hanyu-x]

Mac:~ yu$ sudo port install cairo
Warning: /opt/local/etc/macports/sources.conf specifies invalid source '//rsync://rsync.macports.org/macports/release/tarballs/ports.tar [default]', ignored.
Warning: System headers do not appear to be installed. Most ports should build correctly, but if you experience problems due to a port depending on system headers, please file a ticket at https://trac.macports.org.
Warning: You can install them as part of the Xcode Command Line Tools package by running `xcode-select --install'.
--->  Computing dependencies for cairo
--->  Cleaning cairo
--->  Scanning binaries for linking errors
--->  No broken files found.
--->  No broken ports found.

[ryandesign (Ryan Carsten Schmidt)]

So, what's your question?

The rev-upgrade feature runs after every port installation or upgrade. That's what prints the "Scanning binaries for linking errors", "No broken files found" and "No broken ports found" lines, and those lines show that rev-upgrade found no problems, which is good. If it had found problems, it would have tried to fix them. If you don't want rev-upgrade to run automatically, set revupgrade_autorun no in macports.conf. If you want it to run but only report problems but not fix them, set revupgrade_mode report in macports.conf.

Your terminal output shows two problems:

Warning: /opt/local/etc/macports/sources.conf specifies invalid source '//rsync://rsync.macports.org/macports/release/tarballs/ports.tar [default]', ignored.

You should correct this. It looks like maybe you tried to comment out the line by putting // at the beginning of it, but // is not a valid way to comment out lines in the Tcl language which we use. You could use # instead.

Warning: System headers do not appear to be installed. Most ports should build correctly, but if you experience problems due to a port depending on system headers, please file a ticket at https://trac.macports.org.
Warning: You can install them as part of the Xcode Command Line Tools package by running `xcode-select --install'.

You should install the command line tools, using the xcode-select --install command as shown in the error message.