shell 循环

for

for variable in {list}
do 
  startment1
  startment2
done
# 例子一
#! /bin/bash
for x in 1 2 3 4 5
do
  echo ${x}
done
#例子二
#! /bin/bash
for x in {1..8}
do
  echo ${x}
done
#例子三
#! /bin/bash
for x in {Mon Tue Wed Thu Fri Sat Sun} #大扩号可以省略
do
  echo ${x}
done
#例子四，使用命令作为参数
#! /bin/bash
for x in $(ls) # 也可以直接使用ls或*号通配符，效果一致，注意*不能放到$()中
do
  echo ${x}
done
#例子五
#! /bin/bash
for x in $@ #可以 $* 可以将命令执行入参作为循环对象
do
  echo ${x}
done

for variable
do
 startment1
 startment2
done
# 等价与下面语法
for variable in $@ # 或者$*
do
 startment1
 startment2
done

条件真执行循环

for ((expression1;expression2;expression3))
do
  startment1
  ...
done
for ((i=0;i<10;i++))
do
  echo ${i}
done

array=(1 2 3 4 5)
for day in ${array[*]}
do
  echo ${day}
done

until 一直循环，知道条件成立退出循环

until expression
do
  startment1
  ...
done
i=0
until [[ ${i} -gt 9 ]] # >
do
  let "i+=1"
  echo ${i}
done

批量添加用户和批量删除用户

#! /bin/bash
i=1
until [ ${i} -eq 21 ] # =
do
  useradd user${i} # mac没有这个命令
  echo "password" | passwd --stdin user${i} > /dev/null
  let "i++"
done
#! /bin/bash
i=1
until [ ${i} -eq 21 ] # =
do
  userdel -r user${i} # mac也没有这个命令
  let "i++"
done

while

while expression
do
  startment1
  ...
done
#! /bin/bash
i=1
while [ $i -lt 10 ] # <
do
  echo $i
  let "i++"
done
# 例子二
#! /bin/bash
z=0
for ((i=0;i<10;i++))
do
  for ((j=0;j<10;j++))
  do
    num=$((j % 2))
    if [ $num -eq 0 ]
    then
      continue
    fi
    let "z=i+j"
    echo "z: ${z} ${j} ${num}"
    if [ $z -gt 10 ]
    then
      break 2
    fi
  done
  echo "i: $i"
done