CHAPTER 15 ■ AN INTRODUCTION TO PEAR AND PYRUSDependencies
Although packages are generally stand-alone entities, they often make use of one another. Any use of
another package introduces a dependency. If the used package is not present on the user’s system, then
the package that uses it will not run as expected.
The dependencies tag is a required element, and within it, you must specify at least the PHP, and
PEAR installer versions.
Both php and pearinstall can contain min, max, and exclude elements. exlude defines a version
which will be treated as incompatible with the package, and you can include as many of these as you
need. The pearinstaller element can also contain a recommended element, in which you can set a
preferred installer for the package.
If these or other dependencies within the required element are not satisfied, PEAR will refuse to
install the package by default. A package can depend on another package, a PHP extension (such as zlib
or GD) or a particular version of PHP. Here, I insist that Dialekt has access to the Fandango package at
version 10.5.0 or greater (note, that I add this within the required element):
Notice the channel element; this specifies where pear should search for the package should it be
invoked with the -a flag (which tells it to acquire all dependencies). You must specify either a channel or
a uri element. The uri element should point to a package file:
The package element accepts the same dependency specifiers as pearinstaller, with the addition of
conflicts in which you can define a version with which this package will not work.
In addition to package you could also specify extension, os, or arch. Table 15–3 summarizes these
dependency elements.