Linux Shell Program - array

Linux 下的 Shell 编程之数组常用操作。

Arrays in unix shell?
Working with Arrays in Linux Shell Scripting – Part 8

数组的定义#

定义一个数组 array：

$ array=()
$ array=("A" "B" "ElementC" "ElementE")

整体打印数组内容：

$ echo $array
A B ElementC ElementE
$ echo ${array[@]}
$ echo ${array[*]}

数组长度#

用 ${#数组名[@或*]} 可以得到数组长度。

$ echo ${#array[@]}
$ echo ${#array[*]}
4

访问数组元素#

按索引获取数组元素：

实际索引从1开始。

$ echo ${array[0]}

$ echo ${array[1]}
A
$ echo ${array[2]}
B
$ echo ${array[3]}
ElementC
$ echo ${array[4]}
ElementE

循环遍历数组元素：

for element in "${array[@]}"
do
    echo "$element"
done

遍历结果输出：

A
B
ElementC
ElementE

C 语言写法：

b=0
while [ $b -lt $c ]
do
  echo ${filelist[$b]}
  ((b++))
done

数组索引区间切片#

${array[@]} 代表整个数组，则切片写法如下：

${array[@]:0:2} 表示数组从0（索引为0+1）开始的2个元素，即 ${array[1]}、${array[2]}；
${array[@]:2:3} 表示数组从2（索引为2+1）开始的3个元素；
${array[@]:2} 表示数组从2（索引为2+1）开始，直到结尾；

array=("A" "B" "C" "D" "E")
$ echo ${array[@]:0:2}
A B
$ echo ${array[@]:2:3}
C D E
$ echo ${array[@]:2}
C D E

C风格按照索引写入#

cd $yourpathname
j=0
for i in `ls -1`
do
    folder_list[j]=$i
    j=`expr $j + 1`
done

在shell中把ls的输出存进一个数组变量中

c=0
for file in `ls`
do
  filelist[$c]=$file
  ((c++))
done

或者：

c=0
for file in *
do
  filelist[$c]="$file" # 为了准确起见，此处要加上双引号
  ((c++))
done

或者：

set -a myfiles
index=0
for f in `ls`; do myfiles[index]=$f; let index=index+1; done

注意：用这种方法，如果文件名中有空格的话，会将一个文件名以空格为分隔符分成多个存到数组中，最后出来的结果就是错误的。

把filelist数组内容输出到屏幕上：

b=0
while [ $b -lt $c ]
do
  echo ${filelist[$b]}
  ((b++))
done

或者

b=0
for value in ${filelist[*]}
do
  echo $value
done

用 ${#数组名[@或*]} 可以得到数组长度。

在屏幕上输出filelist数组长度：

echo ${#filelist[*]}

Mutable Access#

How to add/remove an element to/from the array in bash?

Mutable list or array structure in Bash? How can I easily append to it?

add an element at head/tail#

To add an element to the beginning of an array use.

arr=("new_element" "${arr[@]}")

Generally, you would do.

arr=("new_element1" "new_element2" "..." "new_elementN" "${arr[@]}")

To add an element to the end of an array use.

arr=( "${arr[@]}" "new_element" )

Or instead

arr+=( "new_element" )

Generally, you would do.

arr=( "${arr[@]}" "new_element1" "new_element2" "..." "new_elementN")
# Or
arr+=( "new_element1" "new_element2" "..." "new_elementN" )

add an element to specific index#

To add an element to specific index of an array use.

Let's say we want to add an element to the position of Index2 arr[2], we would actually do merge on below sub-arrays:

Get all elements before Index position2 arr[0] and arr[1];
Add an element to the array;
Get all elements with Index position2 to the last arr[2], arr[3], ....

arr=( "${arr[@]:0:2}" "new_element" "${arr[@]:2}" )

removing an element from the array#

In addition to removing an element from an array (let's say element #2), we need to concatenate two sub-arrays.
The first sub-array will hold the elements before element #2 and the second sub-array will contain the elements after element #2.

arr=( "${arr[@]:0:2}" "${arr[@]:3}" )

${arr[@]:0:2} will get two elements arr[0] and arr[1] starts from the beginning of the array.
${arr[@]:3} will get all elements from index3 arr[3] to the last.

Another possibility to remove an element is Using unset (actually assign 'null' value to the element)

unset arr[2]

Use replace pattern if you know the value of your elements.

arr=( "${arr[@]/PATTERN/}" )

text to line array#

在执行 find、grep 等命令时，每一条结果往往对应一行文本，可将文本行管道传输给 xargs 等进行后续处理。

如果当前Shell环境没有安装 sed、awk 等行编辑器，可以将文本文件转换为文本行数组，然后遍历数组进行逐行处理。

array=($(cat issue-file-list.txt)) # array=($(awk 1 issue-file-list.txt))
echo ${#array[*]}

for file in ${array[@]}; do
    clang-format --verbose -style=file -i $file
done

当然，通过行编辑器 sed、awk 来逐行输出，进而执行进一步操作。

sed -n '1,$p' issue-file-list.txt | xargs clang-format --verbose -style=file -i
awk 1 issue-file-list.txt | xargs clang-format --verbose -style=file -i