while_for.sh

# 行迭代
# while 循环法
while read line;do
    echo $line;
done < file.txt

# 命令行法
cat file.txt | (while read line;do echo $line;done)

# awk法
cat file.txt | awk '{print}'

# 单词迭代
for word in $line; do echo $word; done

# 字符迭代
# ${string:start_pos:num_of_chars}：从字符串中提取一个字符；(bash文本切片）
# ${#word}:返回变量word的长度
for((i=0;i<${#word};i++))
do
    echo ${word:i:1);
done