linux shell (三)shell编程

一、基本操作

1、echo $SHELL

2、重定向 >    >>    <    <<

wc << test
> hello world
> just do it
> over
> test
 3  6 28

3、管道 command1 | command2   command1的输出作为command2的输入

4、数学运算

expr num1 opt num2  (opt = + - * / >= <= > < !=  | & %)

$[num1 opt num2]

解决浮点数运算使用bc的scale: c=`echo "scale=5;$a / $b" | bc`

 5、每个命令都有退出状态码 $?

0:命令成功结束

gt 0: 命令出错

exit 0

二、结构化命令

#!/bin/bash
#descrip: it's a test 
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/home/xiaolong.hou/bin:/usr/local/jdk1.7/bin:/usr/local/maven/bin:/usr/local/hadoop-1.2.1/bin

if grep $USER /etc/passwd
then
        echo 'SUCCESS'
else
        echo 'FALIUR'
fi
exit 0

 

 1、test的condition  []

数值比较： -eq  -ge  -gt  -le  -lt  -ne

字符串比较：=   !=    >   <   -n(length is not zero)   -z   (注：大于小于得转义，否则成重定向)

文件比较：-d   -e   -f   -r   -s  -w  -x  -O(is owned by current user?) -G(default group same as current group)   -nt(newer than)   -ot(older than)

 2、复合条件

[ condition1 ] && [ condition2 ]

[ condition1 ] || [ condition2 ]

3、高级特性：(( expresion ))   [[ strExpression字符串比较 ]]

expression：(++   --  !  ~   **   <<   >>    &   |   &&   ||  )  (>  <  =  )    (注：> < 不需要转义)

strExpression：pattern matching

4、case

case var in

    pattern1 | pattern2) command1;;

    pattern3) command2;;

    ...

    *) default command;;

esac

5、for  while  util

for var in list

do

    command

done

更还分隔符：

空格：

制表：

换行：IFS＝$'\n'  $'\t'

IFS.old=IFS

...

IFS=IFS.old

#!/bin/bash
#descrip: test 
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/home/xiaolong.hou/bin:/usr/local/jdk1.7/bin:/usr/local/maven/bin:/usr/local/hadoop-1.2.1/bin
for file in /data/*
do
	if [ -d $file ]
	then
		echo $file is a dictory
	elif [ -f $file ]
	then
		echo $file is a file
	fi
done
exit 0

 

 

 

#!/bin/bash
#descrip: test 
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/home/xiaolong.hou/bin:/usr/local/jdk1.7/bin:/usr/local/maven/bin:/usr/local/hadoop-1.2.1/bin
for((i = 1; i <= 10; i++))
do
        echo "loop test: "$i
done

var=10
while [ $var -gt 0 ]
do
        echo "while test: "$var
        (( var-- ))
done
n=1
until [ $n -eq 10 ]
do
        echo "until test: "$n
        (( n++ ))
done
exit 0

 

#!/bin/bash
#descrip: test 
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/home/xiaolong.hou/bin:/usr/local/jdk1.7/bin:/usr/local/maven/bin:/usr/local/hadoop-1.2.1/bin

IFSOLD=$IFS
IFS=$'\n'
for line in `cat /etc/passwd`
do
        echo "line: "
        IFS=:
        for field in $line
        do
                echo "   "$field
        done
done
IFS=$IFSOLD
exit 0