+
+@node Install Command Categories
+@section Install Command Categories
+
+@cindex pre-installation commands
+@cindex post-installation commands
+When writing the @code{install} target, you must classify all the
+commands into three categories: normal ones, @dfn{pre-installation}
+commands and @dfn{post-installation} commands.
+
+Normal commands move files into their proper places, and set their
+modes. They may not alter any files except the ones that come entirely
+from the package they belong to.
+
+Pre-installation and post-installation commands may alter other files;
+in particular, they can edit global configuration files or data bases.
+
+Pre-installation commands are typically executed before the normal
+commands, and post-installation commands are typically run after the
+normal commands.
+
+The most common use for a post-installation command is to run
+@code{install-info}. This cannot be done with a normal command, since
+it alters a file (the Info directory) which does not come entirely and
+solely from the package being installed. It is a post-installation
+command because it needs to be done after the normal command which
+installs the package's Info files.
+
+Most programs don't need any pre-installation commands, but we have the
+feature just in case it is needed.
+
+To classify the commands in the @code{install} rule into these three
+categories, insert @dfn{category lines} among them. A category line
+specifies the category for the commands that follow.
+
+A category line consists of a tab and a reference to a special Make
+variable, plus an optional comment at the end. There are three
+variables you can use, one for each category; the variable name
+specifies the category. Category lines are no-ops in ordinary execution
+because these three Make variables are normally undefined (and you
+@emph{should not} define them in the makefile).
+
+Here are the three possible category lines, each with a comment that
+explains what it means:
+
+@smallexample
+ $(PRE_INSTALL) # @r{Pre-install commands follow.}
+ $(POST_INSTALL) # @r{Post-install commands follow.}
+ $(NORMAL_INSTALL) # @r{Normal commands follow.}
+@end smallexample
+
+If you don't use a category line at the beginning of the @code{install}
+rule, all the commands are classified as normal until the first category
+line. If you don't use any category lines, all the commands are
+classified as normal.
+
+These are the category lines for @code{uninstall}:
+
+@smallexample
+ $(PRE_UNINSTALL) # @r{Pre-uninstall commands follow.}
+ $(POST_UNINSTALL) # @r{Post-uninstall commands follow.}
+ $(NORMAL_UNINSTALL) # @r{Normal commands follow.}
+@end smallexample
+
+Typically, a pre-uninstall command would be used for deleting entries
+from the Info directory.
+
+If the @code{install} or @code{uninstall} target has any dependencies
+which act as subroutines of installation, then you should start
+@emph{each} dependency's commands with a category line, and start the
+main target's commands with a category line also. This way, you can
+ensure that each command is placed in the right category regardless of
+which of the dependencies actually run.
+
+Pre-installation and post-installation commands should not run any
+programs except for these:
+
+@example
+[ basename bash cat chgrp chmod chown cmp cp dd diff echo
+egrep expand expr false fgrep find getopt grep gunzip gzip
+hostname install install-info kill ldconfig ln ls md5sum
+mkdir mkfifo mknod mv printenv pwd rm rmdir sed sort tee
+test touch true uname xargs yes
+@end example
+
+@cindex binary packages
+The reason for distinguishing the commands in this way is for the sake
+of making binary packages. Typically a binary package contains all the
+executables and other files that need to be installed, and has its own
+method of installing them---so it does not need to run the normal
+installation commands. But installing the binary package does need to
+execute the pre-installation and post-installation commands.
+
+Programs to build binary packages work by extracting the
+pre-installation and post-installation commands. Here is one way of
+extracting the pre-installation commands:
+
+@smallexample
+make -n install -o all \
+ PRE_INSTALL=pre-install \
+ POST_INSTALL=post-install \
+ NORMAL_INSTALL=normal-install \
+ | gawk -f pre-install.awk
+@end smallexample
+
+@noindent
+where the file @file{pre-install.awk} could contain this:
+
+@smallexample
+$0 ~ /^\t[ \t]*(normal_install|post_install)[ \t]*$/ @{on = 0@}
+on @{print $0@}
+$0 ~ /^\t[ \t]*pre_install[ \t]*$/ @{on = 1@}
+@end smallexample
+
+The resulting file of pre-installation commands is executed as a shell
+script as part of installing the binary package.
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