Linux Shell脚本编写——构建基本脚本(一)

创建shell脚本

在创建shell脚本文件，必须在文件的第一行指定要使用的shell，其格式为：

#!/bin/bash

创建、执行sh脚本

代码1-1

root@lejian:/data# cat demo1 #/bin/bashdatewhoroot@lejian:/data# ls -ltotal 4-rw-r--r-- 1 root root 21 Dec  1 13:59 demo1root@lejian:/data# chmod u+x demo1 root@lejian:/data# ls -ltotal 4-rwxr--r-- 1 root root 21 Dec  1 13:59 demo1root@lejian:/data# ./demo1 Thu Dec  1 14:03:57 CST 2016root     pts/0        2016-12-01 13:34 (110.86.16.210)

代码1-1中，chmod u+x demo1 为修改demo1文件权限使其可执行

如果想在同一行显示一个文本字符串和一个命令的输出，可以用echo语句的-n参数，date必须换行，否则将不会打印日期还是打印date

代码1-2

root@lejian:/data# cat demo2 #!/bin/bashecho -n "The time and date are:"datewhoroot@lejian:/data# ./demo2 The time and date are:Thu Dec  1 20:06:19 CST 2016root     pts/0        2016-12-01 19:59 (122.90.139.156)

使用环境变量，和转义美元$符号，如果要打印美元$需要进行转义，否则有可能打印为空或其他已定义的环境变量

代码1-3

root@lejian:/data# cat demo4 #!/bin/bashecho "User info for userid:$USER"echo "UID:$UID"echo "HOME:$HOME"echo "The cost of item is $15"echo "The cost of item is \$15"root@lejian:/data# ./demo4 User info for userid:rootUID:0HOME:/rootThe cost of item is 5The cost of item is $15

用户变量

除了环境变量，shell脚本还允许在脚本中定义和使用自己的变量，定义变量允许临时存储数据并在整个脚本中使用

代码1-4

root@lejian:/data# cat demo5 #!/bin/bashdays=19guest="Tom"echo "$guest checked in $days days ago"days=25guest="Amy"echo "$guest checked in $days days ago"customer=$guestecho "The customer is $customer"root@lejian:/data# ./demo5 Tom checked in 19 days agoAmy checked in 25 days agoThe customer is Amy

反引号

shell脚本中反引号允许将shell命令的输出赋给变量

testing=`date`代码1-5root@lejian:/data# cat demo6 #!/bin/bashtesting=`date`echo "$testing"today=`date +%Y-%m-%d`echo "now is $today"today=`date +%H:%M:%S`echo "now is $today"today=`date "+%Y-%m-%d %H:%M:%S"`echo "now is $today"tomorrow=`date -d tomorrow "+%Y-%m-%d %H:%M:%S"`echo "tomorrow is $tomorrow"yesterday=`date -d yesterday  "+%Y-%m-%d %H:%M:%S"`echo "yesterday is $yesterday"root@lejian:/data# ./demo6 Thu Dec  1 20:45:05 CST 2016now is 2016-12-01now is 20:45:05now is 2016-12-01 20:45:05tomorrow is 2016-12-02 20:45:05yesterday is 2016-11-30 20:45:05

输出重定向

将命令的输出发送到一个文件中，bash shell采用(>)完成输出重定向，采用(>>)完成追加输出重定向

代码1-6

root@lejian:/data# date > demo7root@lejian:/data# cat demo7 Thu Dec  1 20:52:09 CST 2016root@lejian:/data# who > demo7 root@lejian:/data# cat demo7 root     pts/0        2016-12-01 19:59 (122.90.139.156)root@lejian:/data# date >> demo7 root@lejian:/data# cat demo7 root     pts/0        2016-12-01 19:59 (122.90.139.156)Thu Dec  1 20:52:32 CST 2016

输入重定向

将文件的内容重定向到命令，输入重定向的符号（<），内联输入重定向符号是双小于号（<<），除了这个符号，必须指定一个文件标记来划分输入数据的开始和结尾

wc命令是用来打印文件的文本行数、单词数、字节数等默认输出三个值

代码1-7

root@lejian:/data# wc <<EOF> Java> PHP> Python> EOF 3  3 16

管道

有时需要发送某个命令的输出作为另一个命令的输入

代码1-8

root@lejian:/data# cat demo9 hello Javahello Springhello MybatisPHP is the best language in the worldJava is the best language in the worldroot@lejian:/data# cat demo9 | grep Javahello JavaJava is the best language in the world

expr命令允许在命令上上处理数学表达式（注：数字和运算符必须有空格分隔），一些有特殊含义的符号（例如星号），可加上反斜杠转义

代码1-9

root@lejian:/data# expr 1 + 56root@lejian:/data# expr 1 - 5-4root@lejian:/data# expr 1 * 5expr: syntax errorroot@lejian:/data# expr 1 \* 55root@lejian:/data# expr 1 / 50

将一个算术运算式的结果赋给一个变量，需要用引号括起来

代码1-10

root@lejian:/data# cat demo1 #!/bin/bashval1=20val2=10val3=`expr $val1 / $val2`echo "The result is $val3"root@lejian:/data# ./demo1 The result is 2

使用方括号计算

代码1-11

root@lejian:/data# val1=$[1+5]root@lejian:/data# echo $val16root@lejian:/data# val2=$[$val1+10]root@lejian:/data# echo $val216root@lejian:/data# cat demo2 #!/bin/bashval1=5val2=8val3=9val4=1val5=10val6=2val=$[val1+(val2-val3)+val4*val5+val6]echo "The result is $val"root@lejian:/data# ./demo2 The result is 16

bc计算机允许在命令行输入浮点表达式、解释表达式、计算并返回结果，bc计算器能识别：

• 数字(整数和浮点数)
• 变量(简单变量和数组)
• 注释(以#开始的行或C语言的/**/)
• 表达式
• 编程语句(if-then)
• 函数

代码1-12

root@lejian:/data# bcbc 1.06.95Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation, Inc.This is free software with ABSOLUTELY NO WARRANTY.For details type `warranty'. 9.1+11.220.38.1+9.918.0quit

使用-q可以去掉提示语

代码1-13

root@lejian:/data# bc -q3/50scale=33/5.600val1=10val2=6val1*val260val3=val1+val2print val316quit

脚本中使用bc

代码1-14

root@lejian:/data# cat demo3 #!/bin/bashval1=`echo "scale=3;3/6" | bc`echo "The result is $val1"root@lejian:/data# ./demo3 The result is .500

查看退出状态码

Linux提供$?变量来保存上个执行命令的退出状态码

代码1-15

root@lejian:/data# dateFri Dec  2 04:57:24 CST 2016root@lejian:/data# echo $?0root@lejian:/data# aaaNo command 'aaa' found, did you mean: Command 'aha' from package 'aha' (universe) Command 'aa' from package 'astronomical-almanac' (universe) Command 'ara' from package 'ara' (universe) Command 'jaaa' from package 'jaaa' (universe)aaa: command not foundroot@lejian:/data# echo $?127

Linux退出状态码

exit退出命令可以指定退出状态码，但不能超过255，否则会取模

代码1-16

root@lejian:/data# cat demo4 #!/bin/bashdateecho $?whoexit 5root@lejian:/data# ./demo4 Fri Dec  2 05:03:08 CST 20160root     pts/0        2016-12-02 04:39 (122.91.222.126)root@lejian:/data# echo $?5