Arrays All Versions

Examples

• 17

  Array Assignments

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  17

  List Assignment

  Create an array with new elements:

  array=('first element' 'second element' 'third element')
  

  Subscript Assignment

  Create an array with explicit element indices:

  array=([3]='fourth element' [4]='fifth element')
  

  Assignment by index

  array[0]='first element'
  array[1]='second element'
  

  Assignment by name (associative array)

  declare -A array
  array[first]='First element'
  array[second]='Second element'
  

  Dynamic Assignment

  Create an array from the output of other command, for example use seq to get a range from 1 to 10:

  array=(`seq 1 10`)
  

  Assignment from script's input arguments:

  array=("$@")
  

  Assignment within loops:

  while read -r; do
      #array+=("$REPLY")     # Array append
      array[$i]="$REPLY"     # Assignment by index
      let i++                # Increment index 
  done < <(seq 1 10)  # command substitution
  echo ${array[@]}    # output: 1 2 3 4 5 6 7 8 9 10
  

  where $REPLY is always the current input

  edited Aug 29 '16 at 7:57

  

  

  

  

  

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• 10

  Accessing Array Elements

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  10

  Print element at index 0

  echo "${array[0]}"
  

  Print last element (available from Bash 4.3)

  echo "${array[-1]}"
  

  Print all elements

  echo "${array[@]}"
  

  Print all elements as a single string

  echo "${array[*]}"
  

  Print all elements from index 1

  echo "${array[@]:1}"
  

  Print 3 elements from index 1

  echo "${array[@]:1:3}"
  

  String Operations

  If referring to a single element, string-operations are permitted:

  array=(zero one two)
  echo ${array[0]:0:3} # gives out zer (chars at position 0, 1 and 2 in the string zero)
  echo ${array[0]:1:3} # gives out ero (chars at position 1, 2 and 3 in the string zero)
  

  so ${array[$i]:N:M} gives out a string from the N'th position (starting from 0) in the string ${array[$i]} with M following chars

  edited Sep 14 '16 at 23:29

  

  

  

  

  

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• 9

  Array Modification

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  9

  Change Index

  Initialize or update a particular element in the array

  array[10]="elevenths element"    # because it's starting with 0
  

  Append

  Modify array, adding elements to the end if no subscript is specified.

  array+=('fourth element' 'fifth element')
  

  Replace the entire array with a new parameter list.

  array=("${array[@]}" "fourth element" "fifth element")
  

  Add an element at the beginning:

  array=("new element" "${array[@]}")
  

  Insert

  Insert an element at a given index:

  arr=(a b c d)
  # insert an element at index 2
  i=2
  arr=("${arr[@]:0:$i}" 'new' "${arr[@]:$i}")
  echo "${arr[2]}" #output: new
  

  Delete

  Delete array indexes using the unset builtin:

  arr=(a b c)
  echo "${arr[@]}"   # outputs: a b c
  echo "${!arr[@]}"  # outputs: 0 1 2
  unset -v 'arr[1]'
  echo "${arr[@]}"   # outputs: a c
  echo "${!arr[@]}"  # outputs: 0 2
  

  Re-index an array

  This can be useful if elements have been removed from an array, or if you're unsure whether there are gaps in the array. To recreates the indices:

  array=("${array[@]}")
  

  edited Jan 13 at 8:43

  

  

  

  

  

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• 6

  Array Length

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  6

  ${#array[@]} gives the length of the array ${array[@]}:

  array=('first element' 'second element' 'third element')
  echo "${#array[@]}" # gives out a length of 3
  

  This works also with Strings in single elements:

  echo "${#array[0]}"    # gives out the lenght of the string at element 0: 13
  

  edited Aug 28 '16 at 2:57

  

  

  
• 5

  Iterating over entries in an array

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  5

  Arrays can be iterated over easily:

  fileList=( file1.txt file2.txt file3.txt )
  
  # Within the for loop, $file is the current file
  for file in "${fileList[@]}"
  do
    echo "$file"
  done
  

  created Jul 21 '16 at 18:55

  
• 4

  Destroy, Delete, or Unset an Array

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  4

  To destroy, delete, or unset an array:

  unset array
  

  To destroy, delete, or unset a single array element:

  unset array[10]
  

  edited Jul 24 '16 at 14:17

  

  
• 3

  Looping through an array

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  3

  Our example array:

  arr=(a b c d e f)
  

  Using a for..in loop:

  for i in "${arr[@]}"; do
      echo "$i"
  done
  

  Using for loop with numerical conditional:

  for ((i=0;i<${#arr[@]};i++)); do
      echo "${arr[$i]}" 
  done
  

  Using while loop:

  i=0
  while [ $i -lt ${#arr[@]} ]; do
      echo "${arr[$i]}"
      i=$(expr $i + 1)
  done
  

  Using while loop with numerical conditional:

  i=0
  while (( $i < ${#arr[@]} ));do
      echo "${arr[$i]}"
      ((i++))
  done
  

  Using an until loop:

  i=0
  until [ $i -ge ${#arr[@]} ];do
      echo "${arr[$i]}"
      i=$(expr $i + 1)
  done
  

  Using an until loop with numerical conditional:

  i=0
  until (( $i >= ${#arr[@]} )); do
      echo "${arr[$i]}"
      ((i++))
  done
  

  edited Sep 1 '16 at 15:42

  

  
• 2

  List of initialized indexes

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  2

  Get the list of inialized indexes in an array

  $ arr[2]='second'
  $ arr[10]='tenth'
  $ arr[25]='twenty five'
  $ echo ${!arr[@]}
  2 10 25
  

  created Jul 22 '16 at 9:05

  
• 1

  Array insert function

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  1

  This function will insert an element into an array at a given index:

  insert(){
      h='
  ################## insert ########################
  # Usage:
  #   insert arr_name index element
  #
  #   Parameters:
  #       arr_name    : Name of the array variable
  #       index       : Index to insert at
  #       element     : Element to insert
  ##################################################
      '
      [[ $1 = -h ]] && { echo "$h" >/dev/stderr; return 1; }
      declare -n __arr__=$1   # reference to the array variable
      i=$2                    # index to insert at
      el="$3"                 # element to insert
      # handle errors
      [[ ! "$i" =~ ^[0-9]+$ ]] && { echo "E: insert: index must be a valid integer" >/dev/stderr; return 1; }
      (( $1 < 0 )) && { echo "E: insert: index can not be negative" >/dev/stderr; return 1; }
      # Now insert $el at $i
      __arr__=("${__arr__[@]:0:$i}" "$el" "${__arr__[@]:$i}")
  }
  

  Usage:

  insert array_variable_name index element
  

  Example:

  arr=(a b c d)
  echo "${arr[2]}" # output: c
  # Now call the insert function and pass the array variable name,
  # index to insert at
  # and the element to insert
  insert arr 2 'New Element'
  # 'New Element' was inserted at index 2 in arr, now print them
  echo "${arr[2]}" # output: New Element
  echo "${arr[3]}" # output: c
  

  edited Sep 1 '16 at 15:38

  
• 1

  Associative Arrays

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  1

  Associative arrays are supported by Bash 4.0+.

  Declare an associative array

  declare -A aa 
  

  Declaring an associative array before initialization or use is mandatory.

  Initialize elements

  You can initialize elements one at a time as follows:

  aa[hello]=world
  aa[ab]=cd
  aa["key with space"]="hello world"
  

  You can also initialize an entire associative array in a single statement:

  aa=([hello]=world [ab]=cd ["key with space"]="hello world")
  

  Access an Associative Array Element

  echo ${aa[hello]}
  # Out: world
  

  Listing Associative Array Keys

  echo "${!aa[@]}"
  #Out: hello ab key with space
  

  Listing Associative Array Values

  echo "${aa[@]}"
  #Out: world cd hello world
  

  Iterate Over Associative Array Keys and Values

  for key in "${!aa[@]}"; do
      echo "Key:   ${key}"
      echo "Value: ${array[$key]}"
  done
  
  # Out:
  # Key:   hello
  # Value: world
  # Key:   ab
  # Value: cd
  # Key:   key with space
  # Value: hello world
  

  Count Associative Array Elements

  echo "${#aa[@]}"
  # Out: 3
  

  edited Jul 24 '16 at 14:17

  

  
• 0

  Array from string

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  0

  stringVar="Apple Orange Banana Mango"
  arrayVar=(${stringVar// / })
  

  Each space in the string denotes a new item in the resulting array.

  echo ${arrayVar[0]} # will print Apple
  echo ${arrayVar[3]} # will print Mango
  

  Similarly, other characters can be used for the delimiter.

  stringVar="Apple+Orange+Banana+Mango"
  arrayVar=(${stringVar//+/ })
  echo ${arrayVar[0]} # will print Apple
  echo ${arrayVar[2]} # will print Banana
  

  created Jul 23 '16 at 15:00