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www/eps/hpr2756/hpr2756_bash20_ex1.sh

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+#!/bin/bash
+
+#-------------------------------------------------------------------------------
+# Example 1 for Bash Tips show 20: deleting individual array elements
+#-------------------------------------------------------------------------------
+
+#
+# Seed the random number generator with a nanosecond number
+#
+RANDOM=$(date +%N)
+
+echo "Indexed array"
+echo "-------------"
+
+#
+# Create indexed array and populate with ad ae ... cf
+#
+declare -a iarr
+mapfile -t iarr < <(printf '%s\n' {a..c}{d..f})
+
+#
+# Report element count and show the structure
+#
+echo "Length: ${#iarr[*]}"
+declare -p iarr
+
+#
+# Unset a random element
+#
+ind=$((RANDOM % ${#iarr[*]}))
+echo "Element $ind to be removed, contents: ${iarr[$ind]}"
+unset "iarr[$ind]"
+
+#
+# Report on the result of the element removal
+#
+echo "Length: ${#iarr[*]}"
+declare -p iarr
+
+echo
+echo "Associative array"
+echo "-----------------"
+
+#
+# Create associative array. Populate with the indices from the indexed array
+# using the array contents as the subscripts.
+#
+declare -A aarr
+for (( i = 0; i <= ${#iarr[*]}; i++ )); do
+    # If there's a "hole" in iarr don't create an element
+    [[ -v iarr[$i] ]] && aarr[${iarr[$i]}]=$i
+done
+
+#
+# Report element count and keys
+#
+echo "Length: ${#aarr[*]}"
+echo "Keys: ${!aarr[*]}"
+
+#
+# Use a loop to report array contents in sorted order
+#
+for key in $(echo "${iarr[@]}" | sort); do
+    echo "aarr[$key]=${aarr[$key]}"
+done
+
+#
+# Make another contiguous indexed array of the associative array's keys. We
+# don't care about their order
+#
+declare -a keys
+mapfile -t keys < <(printf '%s\n' ${!aarr[*]})
+
+#
+# Unset a random element. The indexed array 'keys' contains the keys
+# of the associative array so we use the selected one as a subscript. We use
+# this array because it doesn't have any "holes". If we'd used 'iarr' we might
+# have hit the "hole" we created earlier!
+#
+k=$((RANDOM % ${#keys[*]}))
+echo "Element '${keys[$k]}' to be removed, contents: ${aarr[${keys[$k]}]}"
+unset "aarr[${keys[$k]}]"
+
+#
+# Report final element count and keys
+#
+echo "Length: ${#aarr[*]}"
+echo "Keys: ${!aarr[*]}"
+declare -p aarr
+
+exit