postrm is in php5-ldap 5.5.9+dfsg-1ubuntu4.
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 | #!/bin/sh
set -e
inidir=/etc/php5/mods-available
for dsoname in ldap ; do
    inifile=${dsoname}.ini
    dpkg-maintscript-helper mv_conffile /etc/php5/conf.d/${inifile} ${inidir}/${inifile} 5.4.0~rc6-1 -- "$@";
    if [ "$1" = "purge" ]; then
        # Query which package has this conffile registered
	if which ucfq >/dev/null; then
	    ucfp=$(ucfq -w ${inidir}/${inifile} | cut -f 2 -d:)
	fi
        # Only work with the config file if it still belongs to us
	if test "$ucfp" = php5-ldap; then
	    for ext in '~' '%' .bak .ucf-new .ucf-old .ucf-dist;  do
		rm -f ${inidir}/${inifile}${ext}
	    done
	    rm -f ${inidir}/${inifile}
	    if which ucf >/dev/null; then
		ucf --purge ${inidir}/${inifile}
	    fi
	    if which ucfr >/dev/null; then
		ucfr --purge php5-ldap ${inidir}/${inifile}
	    fi
	fi
	
	if [ -e /usr/share/php5/php5-maintscript-helper ] ; then
	    . /usr/share/php5/php5-maintscript-helper
	    for dsoname in ldap ; do
		php5_invoke dismod ALL ${dsoname}
	    done
	fi
    fi
done
exit 0
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