This file is indexed.

preinst is in ifupdown 0.7~beta2ubuntu8.

This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.

The actual contents of the file can be viewed below.

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#!/bin/sh
set -e

# Replacing a non-conffile config file with a conffile.  If the config file
# is unmodified, remove it and it will be replaced on unpack.  If it's
# modified, leave it in place and let the usual conffile handling take
# care of it.
config_to_conffile() {
    CONFFILE="$1"
    old_md5sum="$2"

    if [ -e "$CONFFILE" ]; then
        md5sum="`md5sum \"$CONFFILE\" | sed -e \"s/ .*//\"`"
        if [ "$md5sum" = "$old_md5sum" ]; then
            echo "Transitioning $CONFFILE to be a conffile ..."
            rm -f "$CONFFILE"
        fi
    fi
}


if dpkg --compare-versions "$2" lt 0.6.8ubuntu29.1; then
	config_to_conffile /etc/network/if-up.d/upstart \
		4edc4267af9a0bb5aebff50ee4671513
	config_to_conffile /etc/init/network-interface.conf \
		e1f786e36cfe970812604b86ba03a9f0
elif dpkg --compare-versions "$2" lt 0.6.9; then
	config_to_conffile /etc/network/if-up.d/upstart \
		1508668168bca783524789c4c87e28e2
	config_to_conffile /etc/init/network-interface.conf \
		af7f31fee8f6192cae0518454ac2154b
fi

if dpkg --compare-versions "$2" lt 0.6.9; then
	config_to_conffile /etc/init/networking.conf \
		8af8451b188d626e6e7ea92c90d7d64f
	config_to_conffile /etc/init/network-interface-security.conf \
		04449b8f4a377f06cab083dce987ae95
fi

# Try to cleanup bogus dns-* fields added by old netcfg
# the regexp will match any non-commented dns-nameservers line that contains
# a character that's invalid for both IPv4 and IPv6 and comment the line
# FIXME: This code can be dropped in Ubuntu 12.10
if dpkg --compare-versions "$2" lt 0.7~beta2ubuntu7 && [ -w /etc/network/interfaces ]; then
	sed -i '/^[[:space:]]*dns[-_]nameservers[[:space:]]\+/ !b; /^[[:space:]]*dns[-_]nameservers[[:space:]]\+[0-9A-Fa-f.:[:space:]]\+[[:space:]]*\(#.*\)\?$/ b; s/^/#/;s/$/ # disabled by ifupdown/' /etc/network/interfaces
fi