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for

2024年06月27日
柏拉文
越努力，越幸运

一、认识​

Shell支持for循环。

二、语法​

2.1 for value in ${array[@]}​

#!/usr/bin/env bash

array=({item1..itemN}) 
// 或者 
array=$(seq itemm1 itemN)
// 或者 
array=(item1 item2 item3 …… itemN)


for file in ${array[@]}
do 
    command1
    command2
    ...
    commandN
done

2.2 for value in {item1..itemN}; do done​

for value in {item1..itemN};
do 
   command1
    command2
    ...
    commandN
done

for value in {item1..itemN}; do done 使用大括号扩展（Brace Expansion）的方法, 这样可以避免使用子进程来调用 seq 命令，使脚本更高效和直观。

2.2 for value in $(seq item1 itemN); do done​

for value in $(seq item1 itemN); 
do
    command1
    command2
    ...
    commandN
done

for value in $(seq item1 itemN); do done 使用 seq 命令来生成序列

2.4 for value in item1 item2 ... itemN do done​

for var in item1 item2 ... itemN
do
    command1
    command2
    ...
    commandN
done

三、用法​

3.1 循环输出​

for value in {item1..itemN}; do done 方式

#!/usr/bin/env bash

for value in {1..5};
do 
    a=${value}
    b=${value+1}
    echo "a = ${a}, b = ${b}"
done

# 通过 sh test.sh 执行脚本

for value in $(seq item1 itemN); do done 方式

#!/usr/bin/env bash

for value in $(seq 1 5);
do 
    a=${value}
    b=${value+1}
    echo "a = ${a}, b = ${b}"
done

for value in item1 item2 ... itemN do done 方式

#!/usr/bin/env bash

for value in 1 2 3 4 5;
do 
    a=${value}
    b=${value+1}
    echo "a = ${a}, b = ${b}"
done

3.2 批量写入文件​

#!/usr/bin/env bash

fileList=({1..10})
targetDir=$(cd ~/bolawen/scripts/test && pwd)

mkdir -p ${targetDir}

for file in ${fileList[@]}
do 
dir=${targetDir}/${file}.txt
cat <<EOF > ${dir}
This is file ${file} head
This is file ${file} content
This is file ${file} tail
EOF
done