最後更新: 2024-09-25

目錄

• 定義 Array (Explicit / Indirect)
• Access element in array
• Add Item & Pop Item
• Iterate through an array
• ary[*] 與 ary[@] 的分別
• Length of Array
• Copying an Array
• Aarry Extraction
• Load Content of a File into an Array
• Array as command Args

 

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Bash 的 Array

 

Bash 支援以下兩種 Array

• One-dimensional indexed(integers) array
• Associative array

注意

• No maximum limit on the size of an array
  No requirement that members be indexed or assigned contiguously
• Spaces in Array Elements

 

---

定義 Array (Explicit / Indirect)

 

Explicit declaration of an array

Indexed array

declare -a arrayname

Associative arrays

declare -A arrayname

Indirect indexed array declaration

[1] Arrays are assigned to using compound assignments of the form

arrayname[index]=value

#

arrayname[0]="value0"
arrayname[1]="value1"
arrayname[2]="value2"

[2] 使用 "()"

arrayname=(value0 value1 value3)

A) 空的 array

ARRAY=()

B) 多行寫法

arrayname=(
  A 
  B 
  C
)

 

---

Access element in array

 

# Any element of an array may be referenced using

$arrayname                    # 相當於 ${arrayname[0]}

${arrayname}                 # 相當於 ${arrayname[0]}

${arrayname[index]}

 * The braces are required to avoid conflicts with the shell’s filename expansion operators

 

---

Add Item & Pop Item

 

Add Item

array=()                              # 注意 "=" 兩邊沒有空格

array+=('elementToAdd')

Add an element

Unix=("${Unix[@]}" "AIX" "HP-UX")

 

Pop Item

array=("${array[@]:1}")               # removed the 1st element

array=( "${array[@]/$delete}" )    # removes prefixes matching $delete

unset

unset array                   # removes the entire array

unset array[i]                # destroys the element at index

 

---

Iterate through an array

 

#!/bin/bash

# 這樣寫好看點
arrayname=( 
  A 
  B 
  C
)
 
for i in "${array[@]}"
do
  echo "$i"
done

 

 

---

ary[*] 與 ary[@] 的分別

 

# These subscripts differ only when the word appears within double quotes

=> There is no difference if the array expansion is unquoted.

• "${name[*]}"
• "${name[@]}"

當有 quotes 時

• "a[*]" returns a single word that contains all the elements of the array separated by spaces
• "a[@]"  returns each element of the array as an individual word (因此可用於 "for loop" !!)

e.g.

LIST=(1 2 3)

for i in "${LIST[*]}"; do #
  echo "$i"               # result: "1 2 3"
done

for i in "${LIST[@]}"; do
  echo "$i"               # result: 一行一個
done

 

 

---

Length of Array

 

${#array[@]}               # The length of arrary

${#array[index]}          # The length of ${name[subscript]}

 

 

---

Copying an Array

 

Color=(Red Yellow)

NewColor=(${Color[@]})    # 必須加上 (), 否則它成了 STRING

NewColor=${Color[@]}      #  echo ${#NewColor[@]} 的 result 是 1 !!

 

Concatenation 2 Array

MyColor=(${Color[@]} ${NewColor[@]})

 

---

Aarry Extraction

 

Extraction by offset

${array[@]:offset}             

e.g.

ary=(1 2 3 4 5); echo ${ary[@]:2}    # 由第 3 個 Item 開始到尾 (index 由 0 開始)

3 4 5

bash get last n elements of array

echo ${arr[@]:(-3)}

echo  ${arr[@]: -3}    # ":" 與 "-3" 之間的空格必須保留

# The space is required to avoid the interpretation of : followed by a minus - as the expansion of "${var:-abc}" (Use Default Values).

Extraction by offset and length

${array[@]:offset:length}

e.g.

ary=(1 2 3 4 5); echo ${ary[@]::2}      # 相當於由 index 0 開始

ary=(1 2 3 4 5); echo ${ary[@]:2:2}

3 4

 

---

Load Content of a File into an Array

 

#!/bin/bash

filecontent=( `cat "logfile" `)

for t in "${filecontent[@]}"
do
    echo $t
done

 

---

Array as command Args

 

rsync_options=( -rnv --exclude='.*' )

rsync "${rsync_options[@]}" source/ target

remark

"..."   # 是必需的

 

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