Free and open source software is highly modular, and MacPorts ports often require that other ports be installed beforehand; these prerequisites for a given port are called a port's “dependencies”.
The keywords used when specifying dependencies in a Portfile are related to port install phases, and they refer to what are called library, build, fetch, extract and run dependencies. Though all of them install dependencies before a given port is installed, specifying dependencies with the correct keyword is important for proper port upgrade and uninstall behavior, or when running targets other than install. For example, you may not uninstall a port that is a library dependency for another installed port, though you may remove one that is a build dependency. Likewise, if you run the fetch target for a port, only the fetch dependencies will be installed first, so they should be all that is needed for that target.
The list of dependencies to check before phases
fetch, checksum,
extract, patch,
configure, build,
destroot, install, and
package. Fetch dependencies are needed to download
the distfiles for a port, and are not needed at all once the software
is installed.
The list of dependencies to check before phases
extract, patch,
configure, build,
destroot, install, and
package. Extract dependencies are needed to unpack a
port's distfiles into the work directory, and are not needed at all once
the software is installed.
The list of dependencies to check before phases
configure, build,
destroot, install, and
package. Build dependencies are needed when software
is being built, but not needed at all once it is installed.
The list of dependencies to check before phases
configure, build,
destroot, install, and
package. Library dependencies are needed both at
build time (for headers and libraries to link against) and at run
time.
The list of dependencies to check before phase
test.
Test dependencies are only needed when the port enables
testing (i.e. test.run yes).
The list of dependencies to check before phases
destroot, install, and
package. Run dependencies are needed when the
software is run, but not to compile it.
There are two types of dependencies: port dependencies and file dependencies. Port dependencies can be satisfied by reference to a port (the MacPorts registry is queried), or by reference to a file (whether provided by a port or not). The most commonly-used type of dependencies in Portfiles are port dependencies, because dependencies should be provided by MacPorts ported software whenever possible, and usually only one port can provide the needed libraries and files.
But when satisfying a dependency with vendor-supplied software is preferred for special reasons, or when it is possible for more than one port to satisfy a dependency, then file dependencies may be used. An example of the former is with ubiquitous utilities like awk, grep, make or sed, where the versions in macOS are often sufficient; an example of the latter is with “-devel” ports—these ports provide a different version of the same files (though only one can be activated at a time).
Port dependencies, the preferred type, are specified as shown in these examples:
depends_lib port:rrdtool port:apache2 depends_build port:libtool depends_run port:apache2 port:php5
File dependencies should only be used if one of the reasons listed
above applies. There are three types: bin for
programs, lib for libraries, and path
for any installed file. File dependencies are specified in the form:
<type>:<filespec>:<port>.
For bin dependencies,
<filespec> is the name of a program in a
bin directory like ${prefix}/bin, /usr/bin, /bin, and
the associated sbin directories.
For lib dependencies,
<filespec> is the name of a library
(but without its extension) in a lib directory like
${prefix}/lib, /usr/lib, /lib, some Framework
directories, and those found in environment variables like DYLD_LIBRARY_PATH.
For path dependencies,
<filespec> is the complete absolute path
to the file, or more usually, when the file is inside
${prefix}, it is specified relative to
${prefix}.
Since path dependencies are the only ones which would find
files only in an absolute path or a path inside ${prefix}
they are - in cases when a port needs to be more restrictive - often used
instead of bin and lib dependencies .
Note that the <port> specified is
only installed if the specified library, binary, or file is not found. See
the examples below:
depends_lib lib:libX11.6:xorg depends_build bin:glibtool:libtool depends_run path:lib/libltdl.a:libtool