shell双重循环、IFS分隔符、趣味图形、九九乘法表教程

shell双重循环、IFS分隔符、趣味图形、九九乘法表

一、shell脚本值双重循环

1、跳出循环之break命令

for ( (a=1; a<=5; a++) )
do
   echo "outer loop: $a"
   for ( (b=1; b<=50; b++) )
   do
       if [ $b-eq 5 ]
       then
        break           #如果是break 2则代表跳出2层循环
       if
       echo "inter loop: $b"
  done 
done

====================================================================================================================================================================================================================================================================================================================================================================================

2、中止循环之continue命令

• continue中止某次循环中的命令，但不会完全中止整个命令

for ((a=1; a<=15; a++) )
do
   if [ $a -gt 5 ] && [ $a -lt 10 ]
   then
   continue
   fi
   echo "current value: $a"
done

continue和exit的区别

二、IFS分隔符

1、概述

• 默认包含空格，制表符，换行符
• 用 set | grep IFS 命令查看

2、格式

IFS=$' \t\n'

#修改成只换行
IFS=$' \n'
IFS=:
IFS=','

IFS. OLD=$IFS
IFS=$' \n'
...
IFS=$IFS.OLD

3、示例

（1）换行符确认

（2）输出环境变量PATH所包含的所有目录以及其中的所有可执行文件

三、shell趣味图形

1、直线

#!/bin/bash
for ((a=1;a<=20;a++))
do
  echo -n "*"
done
  echo ""

2、矩形

#!/bin/bash

for ((a=1;a<=10;a++))
do
  for ((b=1;b<=15;b++))
  do
  echo -n "*"
  done

 echo ""
done

3、正三角形

#!/bin/bash

a=0

while [ $a -le 9 ]
do
   echo -n "*"
b=1
   while [ $b -le $a ]
do
   echo -n "*"
   let b++
done
   echo ""
   let a++
done

4、倒三角形

#!/bin/bash

a=0

while [ $a -le 9 ]
do
b=8
   while [ $b -ge $a ]
   do
    echo -n "*"  
    let b--
   done
    echo -n "*"
    echo ""
    let a++
done

5、反三角

#!/bin/bash

a=0

while [ $a -le 9 ]
do
   b=9
   while [ $b -ge $a ]
   do
   echo -n " "
   let b--
   done
   c=0
   while [ $c -le $a ]
   do
   echo -n "*"
   let c++
   done
   echo  ''
   let a++
done

6、等腰三角

#!/bin/bash

for ((a=1;a<=9;a++))
do
   for ((b=9;b>=$a;b--))
   do
      echo -n " "
   done

   for ((c=1;c<=$[$a*2-1];c++))
   do
      echo -n "*" 
   done
   echo ""
done

7.平行四边形

#!/bin/bash
for ((i=6;i>=1;i--))
do
 for((k=1;k<=i;k++))
 do
   echo -n " "
 done
  for (( j=6;j>=1;j--))
   do
      echo -n "*"
   done
    echo ""
done

8、等腰梯形

#!/bin/bash
for ((a=1;a<=9;a++))
do
    for ((b=9;b>=$a;b--))
    do
       echo -n " "
    done
    for ((c=1;c<=9;c++))
    do
       echo -n "*"
    done
    for ((d=1;d<=$[$a*2-1];d++))
    do
       echo -n "*"
    done
    echo ""
done

9、菱形

（1）不可变菱形

#!/bin/bash
for ((a=1;a<=9;a++))
do
  for ((b=9;b>=$a;b--))
  do
     echo -n " "
  done
  for ((c=1;c<=$[$a*2-1];c++)) 
  do
     echo -n "*"
  done
     echo ""
done

for ((d=1;d<=10;d++))
do
  for ((e=2;e<=$d;e++))
  do
      echo -n " "
  done
  for ((f=10;f>=$d;f--)) 
  do 
      echo -n "*"
  done
  for ((g=9;g>=$d;g--))
  do
      echo -n "*"
  done

 echo ""
done 

（2）可变大小的菱形

#!/bin/bash

read -p "请输入数字: " i

for ((a=1;a<=$i;a++))
do
   for ((b=$i;b>=$a;b--))
   do
       echo -n " "
   done
   for ((c=1;c<=$[2*a-1];c++))
   do
       echo -n "*"
   done
   echo ""
done

for ((d=$i-1;d>=1;d--))
do
    for ((e=$i;e>=$d;e--))
    do
        echo -n " "
    done
    for ((f=$d;f>=1;f--))
    do
    echo -n "*"
    done
    for ((g=$d;g>1;g--))
    do
    echo -n "*"
done
echo ""
done

四、九九乘法表

#!/bin/bash

for ((a=1;a<=9;a++)) # 1~9循环
do
  for ((b=1;b<=$a;b++))  # 内循环b的值不能超过a
  do 
  c=$[$a*$b]   # a*b等于1*1,2*2
  echo -n -e  "$a*$b=$c\t"   # 输出c的值不换行显示，以及每行空格间隔\t 

  done
echo ""   # 默认隐藏了换行符 \n

done