Added dirhistory plugin.

This plugin navigates directory history using ALT-LEFT and ALT-RIGHT.

plugins/dirhistory/dirhistory.plugin.zsh

+## 
+#   Navigate directory history using ALT-LEFT and ALT-RIGHT. ALT-LEFT moves back to directories 
+#   that the user has changed to in the past, and ALT-RIGHT undoes ALT-LEFT.
+# 
+
+dirhistory_past=(`pwd`)
+dirhistory_future=()
+export dirhistory_past
+export dirhistory_future
+
+export DIRHISTORY_SIZE=30
+
+# Pop the last element of dirhistory_past. 
+# Pass the name of the variable to return the result in. 
+# Returns the element if the array was not empty,
+# otherwise returns empty string.
+function pop_past() {
+  eval "$1='$dirhistory_past[$#dirhistory_past]'"
+  if [[ $#dirhistory_past -gt 0 ]]; then
+    dirhistory_past[$#dirhistory_past]=()
+  fi
+}
+
+function pop_future() {
+  eval "$1='$dirhistory_future[$#dirhistory_future]'"
+  if [[ $#dirhistory_future -gt 0 ]]; then
+    dirhistory_future[$#dirhistory_future]=()
+  fi
+}
+
+# Push a new element onto the end of dirhistory_past. If the size of the array 
+# is >= DIRHISTORY_SIZE, the array is shifted
+function push_past() {
+  if [[ $#dirhistory_past -ge $DIRHISTORY_SIZE ]]; then
+    shift dirhistory_past
+  fi
+  if [[ $#dirhistory_past -eq 0 || $dirhistory_past[$#dirhistory_past] != "$1" ]]; then
+    dirhistory_past+=($1)
+  fi
+}
+
+function push_future() {
+  if [[ $#dirhistory_future -ge $DIRHISTORY_SIZE ]]; then
+    shift dirhistory_future
+  fi
+  if [[ $#dirhistory_future -eq 0 || $dirhistory_futuret[$#dirhistory_future] != "$1" ]]; then
+    dirhistory_future+=($1)
+  fi
+}
+
+# Called by zsh when directory changes
+function chpwd() {
+  push_past `pwd`
+  # If DIRHISTORY_CD is not set...
+  if [[ -z "${DIRHISTORY_CD+x}" ]]; then
+    # ... clear future.
+    dirhistory_future=()
+  fi
+}
+
+function dirhistory_cd(){
+  DIRHISTORY_CD="1"
+  cd $1
+  unset DIRHISTORY_CD
+}
+
+# Move backward in directory history
+function dirhistory_back() {
+  local cw=""
+  local d=""
+  # Last element in dirhistory_past is the cwd.
+
+  pop_past cw 
+  if [[ "" == "$cw" ]]; then
+    # Someone overwrote our variable. Recover it.
+    dirhistory_past=(`pwd`)
+    return
+  fi
+
+  pop_past d
+  if [[ "" != "$d" ]]; then
+    dirhistory_cd $d
+    push_future $cw
+  else
+    push_past $cw
+  fi
+}
+
+
+# Move forward in directory history
+function dirhistory_forward() {
+  local d=""
+
+  pop_future d
+  if [[ "" != "$d" ]]; then
+    dirhistory_cd $d
+    push_past $d
+  fi
+}
+
+
+# Bind keys to history navigation
+function dirhistory_zle_dirhistory_back() {
+  # Erase current line in buffer
+  zle kill-buffer
+  dirhistory_back 
+  zle accept-line
+}
+
+function dirhistory_zle_dirhistory_future() {
+  # Erase current line in buffer
+  zle kill-buffer
+  dirhistory_forward
+  zle accept-line
+}
+
+zle -N dirhistory_zle_dirhistory_back
+# xterm in normal mode
+bindkey "\e[3D" dirhistory_zle_dirhistory_back
+bindkey "\e[1;3D" dirhistory_zle_dirhistory_back
+# Putty:
+bindkey "\e\e[D" dirhistory_zle_dirhistory_back
+# GNU screen:
+bindkey "\eO3D" dirhistory_zle_dirhistory_back
+
+zle -N dirhistory_zle_dirhistory_future
+bindkey "\e[3C" dirhistory_zle_dirhistory_future
+bindkey "\e[1;3C" dirhistory_zle_dirhistory_future
+bindkey "\e\e[C" dirhistory_zle_dirhistory_future
+bindkey "\eO3C" dirhistory_zle_dirhistory_future
+
+