Data commit

Task/Stack/UNIX-Shell/stack-1.sh

@@ -0,0 +1,33 @@
+init() {
+  if [[ -n $KSH_VERSION ]]; then
+    set -A stack
+  else
+    stack=(); # this sets stack to '()' in ksh
+  fi
+}
+
+push() {
+  stack=("$1" "${stack[@]}")
+}
+
+stack_top() {
+  # this approach sidesteps zsh indexing difference
+  set -- "${stack[@]}"
+  printf '%s\n' "$1"
+}
+
+pop() {
+  stack_top
+  stack=("${stack[@]:1}")
+}
+
+empty() {
+  (( ${#stack[@]} == 0 ))
+}
+
+# Demo
+push fred; push wilma; push betty; push barney
+printf 'peek(stack)==%s\n' "$(stack_top)"
+while ! empty; do
+  pop
+done

Task/Stack/UNIX-Shell/stack-2.sh

@@ -0,0 +1,32 @@
+init_stack() {
+  if [[ -n $KSH_VERSION ]]; then
+    eval 'set -A '"$1"
+  else
+    eval "$1=()"
+  fi
+}
+
+push() {
+  eval "$1"'=("$2" "${'"$1"'[@]}")'
+}
+
+stack_top() {
+  eval 'set -- "${'"$1"'[@]}"';
+  printf '%s\n' "$1"
+}
+
+pop() {
+  stack_top "$1";
+  eval "$1"'=("${'"$1"'[@]:1}")'
+}
+
+empty() {
+  eval '(( ${#'"$1"'[@]} == 0 ))'
+}
+
+init_stack mystack
+push mystack fred; push mystack wilma; push mystack betty; push mystack barney
+printf 'peek(mystack)==%s\n' "$(stack_top mystack)"
+while ! empty mystack; do
+  pop mystack
+done