for 變量名 in 取值列表
do                   
   命令序列
done

for i in {1..10}
      或 $(seq 1 10)
      或 ((i=1; i<=10; i++))
do
echo $i
done 

for i in {1..10..2} 
      或 $(seq 1 2 10)
      或 ((i=1; i<=10; i++))
do
echo $i
done 

#!/bin/bash
a=$(cat name.txt)
 for i in a
do
 useradd $i
 echo "123456" | passwd --stdin $i
done

#!/bin/bash
for i in 192.168.100.{1..20}
do
  ping -c 3 -i 0.5 -W 2 $i &> /dev/null
if [ $? = 0 ]
 then
  echo "$i online"
 else
  echo "$i offline"
fi
done

while 條件測(cè)試操作
do
   命令序列
done

#!/bin/bash
i=0
while (($i <=10))
do
echo "$i"
let i++
done

#!/bin/bash
price=$[$RANDOM % 1000]
a=0
times=0
echo "猜猜商品價(jià)格是多少"
while [ $a -eq 0 ]
do
let times++
read -p "請(qǐng)輸入你猜的價(jià)格：" b
if [ $b -eq $price ];then
  echo "yes！"
  let a++
elif [ $b -gt $price ];then
  echo "你猜大了！"
elif [ $b -lt $price ];then
  echo "你猜小了！"
fi
done
echo "你總共猜了 $times 次"

#!/bin/bash
i=0
while [ $i -le 4 ]
 do
 let i++
useradd stu$i
 echo "123456" | passwd --stdin stu$i
done

until 條件測(cè)試操作
do
   命令序列
done

#顯示1-10的整數(shù)
#!/bin/bash
i=1
until [ $i -gt 10 ]
do
 echo "$i"
 let i++
done

#!/bin/bash
i=1
sum=0
until [ $i -gt 50 ]
do
 sum=$(($sum+$i))
 let i++
done
 echo "$sum"

#!/bin/bash
for i in {1..5}
do
echo "外層循環(huán) $i"
 for b in {1..5}
 do
 if [ $b -eq 3 ]
  then
  break
 fi
  echo "內(nèi)層循環(huán) $b"
done
done

#!/bin/bash
for i in {1..5}
 do
  echo "外層循環(huán) $i"
  for b in {1..5}
 do
 if [ $b -eq 3 ]
  then
  continue
 fi
  echo "內(nèi)層循環(huán) $b"
 done
done

1.修改
IFS=$'\t\n'
修改成只換行
IFS=$'\n'
IFS=':'
IFS=','
2.備份
IFS. OLD=$IFS
IFS=$'\n'
...
IFS=$IFS.OLD

#!/bin/bash
OLDIFS=$IFS
IFS=':'
  for i in $PATH
 do
  for a in $i/*
 do
 if [ -x $a -a -f $a ];then
  echo "$a 文件有執(zhí)行權(quán)限"
 fi
 done
done
IFS=$OLDIFS