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<TITLE>Maximum RPM (RPM):Inside the Spec File:EarthWeb Inc.-</TITLE>

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<!-- TITLE=Maximum RPM (RPM)//-->

<!-- AUTHOR=Edward Bailey//-->

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<A NAME="PAGENUM-179"><P>Page 179</P></A>



<P>As you can see, the script starts with the usual invocation of a shell (in this case, the

Bourne shell). There are no arguments passed to the script. Next, a number of environment

variables are set. Here's a brief description of each one:

</P>



<UL>

<LI>     

RPM_SOURCE_DIR&#151;This environment variable gets its value from the

rpmrc file entry sourcedir, which in turn can get part of its value from the

topdir entry. It is the path RPM will prepend to the file, specified in the

source tag line.

<LI>     

RPM_BUILD_DIR&#151;This variable is based on the

builddir rpmrc file entry, which in turn can get part of its value from the

topdir entry. This environment variable translates

to the path of RPM's build directory, where most software will be unpacked and built.

<LI>     

RPM_DOC_DIR&#151;The value of this environment variable is based on the

defaultdocdir rpmrc file entry. Files marked with the

%doc directive can be installed in a subdirectory of

defaultdocdir. For more information on the %doc directive, refer to section 13.6.1.

<LI>    

RPM_OPT_FLAGS&#151;This environment variable gets its value from the

optflags rpmrc file entry. It contains options that can be passed on to the build procedures of the

software being packaged. Normally this means either a configuration script or the

make command itself.

<LI>     

RPM_ARCH&#151;As you might infer from the preceding example, this environment

variable contains a string describing the build system's architecture.

<LI>     

RPM_OS&#151;This one contains the name of the build system's operating system.

<LI>     

RPM_BUILD_ROOT&#151;This environment variable is used to hold the build root, into

which the newly built software will be installed. If no explicit build root has been

specified (either by command-line option, spec file tag line, or

rpmrc file entry), this variable will be null.

<LI>     

RPM_PACKAGE_NAME&#151;This environment variable gets its value from the

name tag line in the package's spec file. It contains the name of the software being packaged.

<LI>     

RPM_PACKAGE_VERSION&#151;The version tag line is the source of this variable's

translation. Predictably, this environment variable contains the software's version number.

<LI>     

RPM_PACKAGE_RELEASE&#151;This environment variable contains the package's

release number. Its value is obtained from the release tag line in the spec file.

</UL>



<P>All these environment variables are set for your use to make it easier to write scripts that will

do the right thing even if the build environment changes.

</P>



<P>The script also sets an option that causes the shell to print out each command, complete

with expanded arguments. Finally, the default permissions are set. Past this point, the scripts

differ. Let's look at the scripts in the order in which they are executed.

</P>



<B>

13.3.1.1. The %prep Script

</B>



<P>The %prep script is the first one RPM executes during a build. Prior to the

%prep script, RPM has performed preliminary consistency checks, such as whether the spec file's

source tag points

</P>



<A NAME="PAGENUM-180"><P>Page 180</P></A>







<P>to files that actually exist. Just prior to passing control over to the

%prep script's contents, RPM changes directory into RPM's build area, which, by default, is

/usr/src/redhat/BUILD.

</P>



<P>At that point, it is the responsibility of the

%prep script to do the following:

</P>



<UL>

<LI>          Create the top-level

build directory.

<LI>          Unpack the original sources into the build directory.

<LI>          Apply patches to the sources, if necessary.

<LI>          Perform any other actions required to get the sources into a ready-to-build state.

</UL>



<P>The first three items on this list are common to the vast majority of all software being

packaged. Therefore, RPM has two macros that greatly simplify these routine functions.

</P>



<P>You can find more information on RPM's %setup and

%patch macros in section 13.4.

</P>



<P>The last item on the list can include creating directories or anything else required to get

the sources into a ready-to-build state. As a result, a

%prep script can range from one line invoking a single

%setup macro to many lines of tricky shell programming.

</P>



<B>

13.3.1.2. The %build Script

</B>



<P>The %build script picks up where the %prep script left off. Once the

%prep script has gotten everything ready for the build, the

%build script is usually somewhat

anticlimactic&#151;normally invoking make, maybe a configuration script, and little else.

</P>



<P>Like %prep before it, the %build script has the same assortment of environment variables

to draw on. Also, like %prep, %build changes directory into the software's top-level build

directory (located in RPM_BUILD_DIR, or usually called

&lt;name&gt;-&lt;version&gt;).

</P>



<P>Unlike %prep, there are no macros available for use in the

%build script. The reason is simple: Either the commands required to build the software are simple (such as a single

make command) or they are so unique that a macro wouldn't make it easier to write the script.

</P>



<B>

13.3.1.3. The %install Script

</B>



<P>The environment in which the %install script executes is identical to those of the other

scripts. Like the other scripts, the %install script's working

directory is set to the software's top-level directory.

</P>



<P>As the name implies, it is this script's responsibility to do whatever is necessary to actually

install the newly built software. In most cases, this means a single

make install command or a few commands to copy files and create directories.

</P>



<B>

13.3.1.4. The %clean Script

</B>



<P>The %clean script, as the name implies, is used to clean up the software's build directory

tree. RPM normally does this for you, but in certain cases (most notably in those packages that

use a build root) you'll need to include a %clean script.

</P>



<A NAME="PAGENUM-181"><P>Page 181</P></A>







<P>As usual, the %clean script has the same set of environment variables as the other scripts

we've covered here. Since a %clean script is normally used when the package is built in a build

root, the RPM_BUILD_ROOT environment variable is particularly useful. In many cases, a simple

</P>

<!-- CODE SNIP //-->

<PRE>

rm -rf $RPM_BUILD_ROOT

</PRE>

<!-- END CODE SNIP //-->



<P>will suffice. Keep in mind that this command in a

%clean script can wreak havoc if used, say, with a build root of

/. Section 12.1.13 in Chapter 12, &quot;rpm -b Command Reference,&quot;

discusses this in more detail.

</P>



<H4>

13.3.2. Install/Erase-Time Scripts

</H4>



<P>The other type of scripts that are present in the spec file are those that are only used when

the package is either installed or erased. There are four scripts, each one meant to be executed

at different times during the life of a package:

</P>



<UL>

<LI>          Before installation

<LI>          After installation

<LI>          Before erasure

<LI>          After erasure

</UL>



<P>Unlike the build-time scripts, there is little in the way of environment variables for these

scripts. The only environment variable available is

RPM_INSTALL_PREFIX, and that is only set if the

package uses an installation prefix.

</P>



<P>Unlike with the build-time scripts, there is an argument defined. The sole argument to

these scripts is a number representing the number of instances of the package currently installed

on the system, after the current package has been installed or erased. Sound tricky? It really

isn't. Here's an example: Assume that a package, called

blather-1.0, is being installed. No previous versions of

blather have been installed. Because the software is being installed, only the

%pre and %post scripts are executed. The argument passed to these scripts will be

1 since the number of blather packages installed is

1. (Or it will be 1 once the package is completely

installed. Remember that the number is based on the number of packages installed after the

current package's install or erase has completed.)

</P>



<P>Continuing our example, a new version of the

blather package, version 1.3, is now available. Clearly it's time to upgrade. What will the scripts' values be during the upgrade? As

blather-1.3 is installing, its %pre and %post scripts will have an argument equal to

2 (1 for version 1.0 already installed, plus 1 for version 1.3 being installed). As the final part of the upgrade,

it's then time to erase blather version 1.0. As the package is being removed, its

%preun and %postun scripts are executed. Since there will be only one

blather package (version 1.3) installed after version 1.0 is erased, the argument passed to version 1.0's scripts is

1.

</P>



<P>To bring an end to this example, we've decided to erase

blather 1.3. We just don't need it anymore. As the package is being erased, its

%preun and %postun scripts will be executed.

</P>



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