#!/bin/bash # empty-array.sh # Thanks to Stephane Chazelas for the original example, #+ and to Michael Zick for extending it. # An empty array is not the same as an array with empty elements. array0=( first second third ) array1=( '' ) # "array1" consists of one empty element. array2=( ) # No elements . . . "array2" is empty. echo ListArray() { echo echo "Elements in array0: ${array0[@]}" echo "Elements in array1: ${array1[@]}" echo "Elements in array2: ${array2[@]}" echo echo "Length of first element in array0 = ${#array0}" echo "Length of first element in array1 = ${#array1}" echo "Length of first element in array2 = ${#array2}" echo echo "Number of elements in array0 = ${#array0[*]}" # 3 echo "Number of elements in array1 = ${#array1[*]}" # 1 (Surprise!) echo "Number of elements in array2 = ${#array2[*]}" # 0 } # =================================================================== ListArray # Try extending those arrays. # Adding an element to an array. array0=( "${array0[@]}" "new1" ) array1=( "${array1[@]}" "new1" ) array2=( "${array2[@]}" "new1" ) ListArray # or array0[${#array0[*]}]="new2" array1[${#array1[*]}]="new2" array2[${#array2[*]}]="new2" ListArray # When extended as above; arrays are 'stacks' # The above is the 'push' # The stack 'height' is: height=${#array2[@]} echo echo "Stack height for array2 = $height" # The 'pop' is: unset array2[${#array2[@]}-1] # Arrays are zero-based, height=${#array2[@]} #+ which means first element has index 0. echo echo "POP" echo "New stack height for array2 = $height" ListArray # List only 2nd and 3rd elements of array0. from=1 # Zero-based numbering. to=2 # array3=( ${array0[@]:1:2} ) echo echo "Elements in array3: ${array3[@]}" # Works like a string (array of characters). # Try some other "string" forms. # Replacement: array4=( ${array0[@]/second/2nd} ) echo echo "Elements in array4: ${array4[@]}" # Replace all matching wildcarded string. array5=( ${array0[@]//new?/old} ) echo echo "Elements in array5: ${array5[@]}" # Just when you are getting the feel for this . . . array6=( ${array0[@]#*new} ) echo # This one might surprise you. echo "Elements in array6: ${array6[@]}" array7=( ${array0[@]#new1} ) echo # After array6 this should not be a surprise. echo "Elements in array7: ${array7[@]}" # Which looks a lot like . . . array8=( ${array0[@]/new1/} ) echo echo "Elements in array8: ${array8[@]}" # So what can one say about this? # The string operations are performed on #+ each of the elements in var[@] in succession. # Therefore : Bash supports string vector operations #+ if the result is a zero length string, #+ that element disappears in the resulting assignment. # Question, are those strings hard or soft quotes? zap='new*' array9=( ${array0[@]/$zap/} ) echo echo "Elements in array9: ${array9[@]}" # Just when you thought you where still in Kansas . . . array10=( ${array0[@]#$zap} ) echo echo "Elements in array10: ${array10[@]}" # Compare array7 with array10. # Compare array8 with array9. # Answer: must be soft quotes. exit 0
