dir_stack.shlib

type pushd >/dev/null 2>&1 || pushd() {
  # === Initialize ===================================================
  case "${DIR_STACK:-}" in '') DIR_STACK=$(pwd);; esac
  # === Try to change directory ======================================
  cd "$1" >/dev/null 2>&1 || {
    echo "${0##*/}: pushd: $1: No such file or directory" 1>&2
    return 1
  }
  # === Push the directory stack =====================================
  DIR_STACK=$(printf '%s\n%s' "$(pwd)" "$DIR_STACK")
  # === Print the contents in the stack ==============================
  printf '%s' "$DIR_STACK"                                                     |
  awk '# --- Replace the prefix of the homedirectory path with "~" if possible #
       BEGIN {homedir=ENVIRON["HOME"];                                         #
              hd_len =length(homedir);                                         #
              while (getline dir) {                                            #
                if ( homedir == ""                  ) {print dir; continue;}   #
                if ((homedir == "/") && (dir != "/")) {print dir; continue;}   #
                pos  =index(dir,homedir);                                      #
                if ( pos     != 1                   ) {print dir; continue;}   #
                print "~" substr(dir,pos+hd_len);                              #
              }                                                             }' |
  tr '\n' ' '                                                                  |
  grep ''                                                                      |
  sed 's/ $//'
}

type popd >/dev/null 2>&1 || popd() {
  # === Initialize ===================================================
  set -- "$(printf '%s\n' "${DIR_STACK:-}" | tail -n +2)"
  set -- "$1" "$(printf '%s\n' "$1" | head -n 1)"
  case "$2" in '') echo "${0##*/}: popd: directory stack empty" 1>&2; return 1;; esac
  # === Try to change directory to the top of the stack ==============
  cd "$2" >/dev/null 2>&1 || {
    echo "${0##*/}: popd: $1: No such file or directory" 1>&2
    return 1
  }
  # === Pop the directory stack ======================================
  DIR_STACK=$1
  # === Print the contents in the stack ==============================
  printf '%s\n' "$1"                                                           |
  awk '# --- Replace the prefix of the homedirectory path with "~" if possible #
       BEGIN {homedir=ENVIRON["HOME"];                                         #
              hd_len =length(homedir);                                         #
              while (getline dir) {                                            #
                if ( homedir == ""                  ) {print dir; continue;}   #
                if ((homedir == "/") && (dir != "/")) {print dir; continue;}   #
                pos  =index(dir,homedir);                                      #
                if ( pos     != 1                   ) {print dir; continue;}   #
                print "~" substr(dir,pos+hd_len);                              #
              }                                                             }' |
  tr '\n' ' '                                                                  |
  grep ''                                                                      |
  sed 's/ $//'
}