#!/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" has 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[@]}
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
