Implement multiple persisted sessions.

* cdlog.sh (cdlog.update): Name of file is now in $cdlog_dirs.
(cdlog.get_param): New function.
(cdlog.init): Implement the LRU session selection and optional
recovery. The variable $cdlog_dirs is established, pointing
to the selected session file.
(mainline): Run cdlog.init if $cdlog_dirs is empty.

* README.md: Documented.

2 files changed, 79 insertions, 9 deletions

diff --git a/README.md b/README.md
index db9a0a1..53d26c8 100644
--- a/README.md
+++ b/README.md
@@ -55,11 +55,17 @@ same directory you are already in. There is no effect on the FIFO.
 ## Persistence
 
 Whenever the nine-element FIFO changes, the current directory and the
-contents of the FIFO are written to the file `~/.cslog.dirs`,
-one path per line.  When `cdlog` initializes, it reads the contents of that
-file. It changes to the directory indicated in the first line, and
-stuffs the remaining nine lines into the FIFO, thereby recovering
-your session.
+contents of the FIFO are written to the file `~/.cslog.N.dirs`,
+one path per line, where `N` is an internal session number.
+
+When `cdlog` initializes, it allocates a session by finding a free
+value `N` in the range 1 to 10. If it cannot find one due to the
+session store being full, it erases the one with the oldest time
+stamp and chooses its index.
+
+When one or more persisted session are present, `cdlog`'s initialization
+presents you with a numbered list of these sessions. You can recover to one of
+the sessions or press Enter to go with the newly allocated one.
 
 ## How is this better?
 
diff --git a/cdlog.sh b/cdlog.sh
index ea585ad..32c65de 100644
--- a/cdlog.sh
+++ b/cdlog.sh
@@ -10,7 +10,7 @@ cdlog.update()
   w=$c4
 
   # Persist to disk.
-  cat > ~/.cdlog.dirs <<!
+  cat > "$cdlog_dirs" <<!
 $PWD
 $c1
 $c2
@@ -34,17 +34,81 @@ cdlog.args()
   cdlog.update
 }
 
+# Utility for nth positional param
+cdlog.get_param()
+{
+    shift $1
+    echo "$1"
+}
+
 # Read state from ~/.cdlog.dirs
 cdlog.init()
 {
   local -a d
+  local dir
+  local i
+  local oldest
+  local context
+  local sel
 
   c9=; c8=; c7=
   c6=; c5=; c4=
   c3=; c2=
 
-  if [ -f ~/.cdlog.dirs ] ; then
-    mapfile -t d < ~/.cdlog.dirs
+  cdlog_dirs=
+  context=
+
+  for i in {1..10}; do
+    if ! [ -f ~/.cdlog.$i.dirs ] ; then
+      context=$i
+      break
+    fi
+  done
+
+  if ! [ $context ] ; then
+    oldest=1
+    for i in {2..10}; do
+      if [ ~/.cdlog.$i.dirs -ot ~/.cdlog.$oldest.dirs ] ; then
+        oldest=$i
+      fi
+    done
+    context=$oldest
+  fi
+
+  cdlog_dirs=~/.cdlog.$context.dirs
+
+  rm -f $cdlog_dirs
+
+  set -- ~/.cdlog.*.dirs
+
+  if [ $# -gt 0 -a $1 != ~/.cdlog.'*'.dirs ] ; then
+    printf "These cdlog contexts exist:\n"
+    i=1
+    for dir in "$@"; do
+      printf "[%d]: %s\n" $((i++)) "$(date -r "$dir")"
+      sed -e '/^$/d' "$dir"
+    done
+
+    while true; do
+      printf "Make a selection or press Enter for new context: "
+      read sel
+      case $sel in
+      ( [1-9] )
+        sel=$(cdlog.get_param $sel "$@")
+        if [ -n "$sel" ] ; then
+          cdlog_dirs=$sel
+          break
+        fi
+        ;;
+      ( "" )
+        break
+        ;;
+      esac
+    done
+  fi
+
+  if [ -f "$cdlog_dirs" ] ; then
+    mapfile -t d < "$cdlog_dirs"
     command cd "${d[0]}"
     unset d[0]
     cdlog.args "${d[@]}"
@@ -213,7 +277,7 @@ shopt -s direxpand
 
 c1=${c1-}
 
-if [ -z "$c1" ] ; then
+if [ -z "$c1" -o -z "$cdlog_dirs" ] ; then
   cdlog.init
 fi