postrm is in libnss-gw-name 0.3-2.
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.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47  | #!/bin/sh
set -e
# Automatically added by dh_makeshlibs
if [ "$1" = "remove" ]; then
	ldconfig
fi
# End automatically added section
if [ "$1" = "remove" ]; then 
	ldconfig
fi
# This code was taken from nss-mdns:
log() {
    echo "$*"
}
remove_nss_entry() {
    log "Checking NSS setup..."
    # abort if /etc/nsswitch.conf does not exist
    if ! [ -e /etc/nsswitch.conf ]; then
        log "Could not find /etc/nsswitch.conf."
        return
    fi
    perl -i -pe '
        my @remove=(
            "gw_name",
        );
        sub remove {
            my $s=shift;
            foreach my $bit (@remove) {
                $s=~s/\s+\Q$bit\E//g;
            }
            return $s;
        }
        s/^(hosts:)(.*)/$1.remove($2)/e;
    ' /etc/nsswitch.conf
}
action="$1"
if [ "$action" = remove ]; then
    remove_nss_entry
fi
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