postinst is in spawn-fcgi 1.6.3-1.
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 | #! /bin/sh -e
# postinst script for spawn-fcgi
update-alternatives \
    --install /usr/bin/spawn-fcgi \
        spawn-fcgi /usr/bin/spawn-fcgi.standalone 10 \
    --slave /usr/share/man/man1/spawn-fcgi.1.gz \
        spawn-fcgi.1.gz /usr/share/man/man1/spawn-fcgi.standalone.1.gz
exit 0
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