Linux - Shell编程基础

用户和操作系统之间的接口

Shell分类

Shell的双重角色

命令解释程序Shell的工作步骤打印提示符得到命令行解析命令查找文件准备参数执行命令独立的程序设计语言解释器KISS (Keep It Small and Stupid)可复用工具tools重定向和管道

也称Shell script(Shell脚本)
是一组命令

#!/bin/shls -altouch aacp aa bb

Shell编程的基础知识
Linux环境
Linux命令
Shell程序结构

Shell脚本的执行方法

#!/bin/sh# first.sh# This file looks through all the files in the current# directory for the string POSIX, and then displays those# files to the standard outputfor file in *do     if grep –q POSIX $file     then          more $file     fidoneexit 0

方法1$ sh script_file 方法2chmod +x script_file (可选chown, chgrp)./script_file方法3source script_file，或.script_file

Shell启动文件

sh/etc/profile        login shell, system wide~/.profile         login shellENVcsh/etc/csh.cshrc       always, system wide/etc/csh.login       login shell, system wide~/.cshrc            always~/.login            login shell~/.logout           logout shell/etc/csh.logout      logout shell, system widetcsh~/.tcshrc          login shellbash/etc/profile  ~/.bash_profile  ~/.bash_login  ~/.bash_profile/etc/bash.bashrc  ~/.bashrcBASH_ENV

Shell输入/输出重定向举例

>：输出重定向$ ls –l > lsoutput.txt >>：追加$ ps >> lsoutput.txt出错输出重定向 (2>)$ kill –HUP 1234 > killout.txt 2> error.txt<：输入重定向$ more < killout.txt

Shell程序设计的语法

Shell环境变量

Shell变量赋值

    $ salutation=Hello$ echo $salutationHello$ salutation="Yes Dear"$ echo $salutationYes Dear$ salutation=7+5$ echo $salutation7+5

Shell变量访问

% echo “$PAGER”% echo “${PAGER}”使用{}避免歧异% temp_name=“haha”% temp=“hehe”% echo $temphehe% echo $temp_namehaha% echo ${temp}_namehehe_name% echo ${temp_name}haha

参数变量和内部变量举例1
假设脚本名为myscript
如果执行./myscript foo bar baz，结果如何？

#!/bin/shsalutation="Hello"echo $salutationecho "The program $0 is now runnning"echo "The 1st & the 2nd parameters were $1 & $2"echo $*exit 0

$ ./myscript foo bar bazHelloThe program ./myscript is now runnningThe 1st & the 2nd parameters were foo & barfoo bar baz

参数变量和内部变量举例2
假设脚本名为var3.sh
执行sh ./var3.sh hello world earth，输入如何？

#!/bin/sh echo "I was called with $# parameters" echo "My name is $0" echo "My first parameter is $1"echo "My second parameter is $2"echo "All parameters are $@"

$ sh ./var3.sh hello world earthI was called with 3 parameters My name is ./var3.sh My first parameter is hello My second parameter is world All parameters are hello world earth

参数变量和内部变量举例3

1  #!/bin/sh 2  echo "What is your name?" 3  read USER_NAME 4  echo "Hello $USER_NAME" 5  echo "File ${USER_NAME}_file will be created" 6  touch "${USER_NAME}_file" 

代码说明
第5行使用USERNAMEfile来确保shell将使用变量USER_NAME，而不是 USERNAMEfile第6行使用“{USER_NAME}_file”避免任何输入给$USER_NAME的空格

Shell变量引用

当包含一个或多个空格时使用”…”
当variable被双引用包含时，将被其值取代当variable被单引号（‘….’）引用时，不会被替换
在variable前带有\时，将取消上述特殊含义一般而言，字符串用双引号引用，以便避免被空格分隔，但允许使用来替换

Shell变量引用举例

#!/bin/shmyvar="Hi there"echo $myvar                echo "$myvar"          echo '$myvar'          echo \$myvar           echo Enter some text        read myvar              echo '$myvar' is $myvar        exit 0

                                                  Output#!/bin/shmyvar="Hi there"echo $myvar                        Hi thereecho "$myvar"          Hi thereecho '$myvar'$myvarecho \$myvar               $myvarecho Enter some text            Enter some textread myvar              Helloecho '$myvar' is $myvar        $myvar is Helloexit 0