POSTIN

<lua>

bashfound = false;
shfound = false;
 
f = io.open("/etc/shells", "r");
if f == nil
then
  f = io.open("/etc/shells", "w");
else
  repeat
    t = f:read();
    if t == "/bin/bash"
    then
      bashfound = true;
    end
    if t == "/bin/sh"
    then
      shfound = true;
    end
  until t == nil;
end
f:close()
 
f = io.open("/etc/shells", "a");
if not bashfound
then
  f:write("/bin/bash\n")
end
if not shfound
then
  f:write("/bin/sh\n")
end
f:close()

POSTUN

/bin/sh

if [ "$1" = 0 ]; then
    /bin/grep -v '^/bin/bash$' < /etc/shells | \
      /bin/grep -v '^/bin/sh$' > /etc/shells.new
    /bin/mv /etc/shells.new /etc/shells
fi