Modifying a File by Using The build Class
This case study modifies a file which exists on the installation machine during
package installation. It uses one of three modification methods. The other two methods
are described in Modifying a File by Using Standard Classes and Class Action Scripts and Modifying a File by Using the sed Class and a postinstall Script. The file modified is /etc/inittab.
This case study demonstrates how to use the build class. For more information
on the build class, see The build Class Script.
This approach to modifying /etc/inittab uses the build class. A build class
script is executed as a shell script and its output becomes the new
version of the file being executed. In other words, the data file /etc/inittab
that is delivered with this package will be executed and the output of
that execution will become /etc/inittab.
The build class script is executed during package installation and package removal. The
argument install is passed to the file if it is being executed at
installation time. Notice in the sample build class script that installation actions are defined
by testing for this argument.
To edit /etc/inittab using the build class, you must complete the following tasks:
Define the build file in the prototype file.
The entry for the build file in the prototype file should place it in the build class and define its file type as e. Be certain that the CLASSES parameter in the pkginfo file is defined as build.
Create the build class script.
The sample build class script performs the following procedures:
Edits the /etc/inittab file to remove any existing changes for this package. Notice that the file name /etc/inittab is hardcoded into the sed command.
If the package is being installed, adds the new line to the end of /etc/inittab. A comment tag is included in this new entry to describe where that entry came from.
Executes the init q command.
This solution addresses the drawbacks described in the case studies in Modifying a File by Using Standard Classes and Class Action Scripts and
Modifying a File by Using the sed Class and a postinstall Script. Only one short file is needed (beyond the pkginfo and prototype
files). The file works with multiple instances of a package since the PKGINST
parameter is used, and no postinstall script is required since the init q command can
be executed from the build class script.
Case Study Files
The pkginfo File
NAME=Case Study #6
The prototype File
e build /etc/inittab ? ? ?
The Build File
# PKGINST parameter provided by installation service
# remove all entries from the existing table that
# are associated with this PKGINST
sed -e "/^[^:]*:[^:]*:[^:]*:[^#]*#$PKGINST$/d" /etc/inittab ||
if [ "$1" = install ]
# add the following entry to the table
echo "rb:023456:wait:/usr/robot/bin/setup #$PKGINST" ||
/sbin/init q ||