postinst is in perl 5.14.2-6ubuntu2.
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 | #!/bin/sh -e
if [ "$1" = configure ]
then
    # The 5.6.0 packages had /usr/share/doc/perl as a symlink to
    # perl-base, now the reverse.
    docs=/usr/share/doc
    if [ -L $docs/perl ] && [ ! -L $docs/perl-base ] && [ -d $docs/perl-base ]
    then
    rm -f $docs/perl
    mv $docs/perl-base $docs/perl
    ln -s perl $docs/perl-base
    fi
    # util-linux has an alternate rename
    update-alternatives --install /usr/bin/rename rename /usr/bin/prename 60 \
    --slave /usr/share/man/man1/rename.1.gz rename.1.gz \
        /usr/share/man/man1/prename.1.gz
    if which dpkg-trigger >/dev/null 2>&1 && \
       [ -n "$2" ] && \
       dpkg --compare-versions "$2" lt 5.14.0
    then
        dpkg-trigger perl-major-upgrade
    fi
fi
exit 0
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