PREUN

/bin/sh

if [ "$1" = "0" ]; then if [[ -f /usr/share/info/bison.info.xz ]]; then /sbin/install-info /usr/share/info/bison.info.xz --dir=/usr/share/info/dir --remove ; fi; fi 
if [ $1 -eq 0 ]; then
  /usr/sbin/update-alternatives --remove yacc /usr/bin/yacc.bison
fi

POSTIN

/bin/sh

if [[ -f /usr/share/info/bison.info.xz ]]; then /sbin/install-info /usr/share/info/bison.info.xz --dir=/usr/share/info/dir; fi 
/usr/sbin/update-alternatives --install /usr/bin/yacc yacc /usr/bin/yacc.bison 10

Triggers

byacc <= 1.9-16mdk

/bin/sh

/usr/sbin/update-alternatives --install /usr/bin/yacc yacc /usr/bin/yacc.bison 10