shell-流程控制

for语句

数字循环1

#!/bin/bash
for((i=1;i<=3;i++));
do
    echo ${i}
done

数字循环2

#!/bin/bash
for i in $(seq 1 3);
do
    echo ${i}
done

数字循环3

#!/bin/bash
for i in {1..3};
do
    echo ${i}
done

数字循环4

#!/bin/bash
awk ‘BEGIN{for(i=1; i<=3; i++) print i}‘

字符循环1

#!/bin/bash
for s in "hello";
do
    echo ${s}
done

字符循环2

#!/bin/bash
for c in $*;
do
    echo ${c} is the input char
done

字符循环3

#!/bin/bash
for c in 1 2 3;
do
    echo ${c}
done

字符循环4

#!/bin/bash
str1="hello world"
for c in ${str1};
do
    echo ${c}
done

路径循环1

#!/bin/bashfor file in /proc/*;  
do  
    echo $file is file path \! ;  
done

路径循环2

#!/bin/bash  
for file in $(ls *.sh)  
do  
echo $file is file path \! ;  
done

while语句

用于执行一系列命令和从输入文件中读取数据

#!/bin/bash
x=1
while((${x}<5));
do
    echo ${x}
    #let "x++"
    x=`expr ${x} + 1`
done

说明：let命令，用于执行一个或多个表达式，变量计算中不需要加上$来表示变量

无限循环

#!/bin/bash
while true
do
    echo 1
done

or

#!/bin/bash
for((;;));
do
    echo 1
done

until语句

用于执行一系列命令直至条件为true时停止，一般while优于until

#!/bin/bash
x=1
until((x>3));
do
    echo ${x}
    x=`expr ${x} + 1`
done

case语句

#!/bin/bash
score="A"

case ${score} in
    "A") echo "A SCORE"
    ;;
    "B") echo "B SCORE"
    ;;
    *) echo "UNKNOWN SCORE"
esac

运算符

比较运算符

-gt    大于

-lt     小于

-eq   等于

==    等于则条件为真

!=     不等于则条件为真

-z     字符串长度为0则为真

-n     字符串长度不为0则为真

逻辑运算符

-a    并且

-o    或者

参考资料：Linux下Shell的for循环语句

参考资料：《与shell脚本编程大全》