Save shell history between sessions

- Inspired by https://gist.github.com/jan-warchol/89f5a748f7e8a2c9e91c9bc1b358d3ec

sync-history.sh

@@ -0,0 +1,58 @@
+# Synchronize history between bash sessions
+#
+# Make history from other terminals available to the current one. However,
+# don't mix all histories together - make sure that *all* commands from the
+# current session are on top of its history, so that pressing up arrow will
+# give you most recent command from this session, not from any session.
+#
+# Since history is saved on each prompt, this additionally protects it from
+# terminal crashes.
+
+
+# keep unlimited shell history because it's very useful
+export HISTFILESIZE=-1
+export HISTSIZE=-1
+shopt -s histappend   # don't overwrite history file after each session
+export HISTFILE=~/.bash/.bash_history
+
+# on every prompt, save new history to dedicated file and recreate full history
+# by reading all files, always keeping history from current session on top.
+update_history () {
+  history -a ${HISTFILE}.$$
+  history -c
+  history -r  # load common history file
+  # load histories of other sessions
+  for f in `ls ${HISTFILE}.[0-9]* 2>/dev/null | grep -v "${HISTFILE}.$$\$"`; do
+    history -r $f
+  done
+  history -r "${HISTFILE}.$$"  # load current session history
+}
+if [[ "$PROMPT_COMMAND" != *update_history* ]]; then
+  export PROMPT_COMMAND="update_history; $PROMPT_COMMAND"
+fi
+
+# merge session history into main history file on bash exit
+merge_session_history () {
+  if [ -e ${HISTFILE}.$$ ]; then
+    cat ${HISTFILE}.$$ >> $HISTFILE
+    \rm ${HISTFILE}.$$
+  fi
+}
+trap merge_session_history EXIT
+
+
+# detect leftover files from crashed sessions and merge them back
+active_shells=$(pgrep `ps -p $$ -o comm=`)
+grep_pattern=`for pid in $active_shells; do echo -n "-e \.${pid}\$ "; done`
+orphaned_files=`ls $HISTFILE.[0-9]* 2>/dev/null | grep -v $grep_pattern`
+
+if [ -n "$orphaned_files" ]; then
+  echo Merging orphaned history files:
+  for f in $orphaned_files; do
+    echo "  `basename $f`"
+    \cat $f >> $HISTFILE
+    \rm $f
+  done
+  echo "done."
+fi
+