Detailed explanation of examples of library management system implemented in Linux shell

#!/bin/bash 
#author:zhanghongjun 
#version:1.0 
#date:2011年 12月 14日 星期三 21:18:18 CST 
 
 
function information 
{ 
  echo "---------------------------" 
  echo "图书馆管理系统（5.4版本）" 
  echo  
  echo -n "| " ;echo "1:添加图书" 
  echo -n "| " ;echo "2:删除图书" 
  echo -n "| " ;echo "3:图书列表" 
  echo -n "| " ;echo "4:查找图书" 
  echo -n "| " ;echo "5|q:退出系统" 
  echo  
  echo "---------------------------" 
  read -p "请输入你的选择:" a 
   
 
  case "$a" in 
  1) 
    add ;; 
  2) 
    delete ;; 
  3) 
    list ;; 
  4) 
    search;; 
  5|q|Q) 
    return -1 ;; 
  *) 
    information ;; 
  esac 
} 
 
 
function file_exist 
{ 
  if [ ! -f .book.txt ];then 
    touch .book.txt 
  fi 
} 
 
 
function add 
{ 
  read -p "请输入图书的编号：" number 
  read -p "请输入图书的书名：" book_name 
  read -p "请输入图书的作者：" author 
  read -p "请输入图书的价格：" price  
    echo -e "$number\t$book_name\t$author\t$price" >>.book.txt && { 
      echo "添加图书成功！" 
      echo "-------------------" 
    } 
  if [ $? -ne 0 ];then 
    echo "添加图书失败" 
  fi 
  information 
 
} 
 
function delete 
{ 
  read -p "请输入要删除的图书的编号：" number 
  grep $number .book.txt &>/dev/null && { 
      sed -i &#39;/\<&#39;$number&#39;\>/d&#39; .book.txt &>/dev/null && 
      echo "删除图书成功"  
  echo "-------------------------" 
  } 
   
  if [ $? -ne 0 ];then 
    echo "删除图书失败" 
    echo "你要删除的图书不存在" 
  fi 
  information 
} 
 
#列出所有图书的信息 
function list 
{ 
  echo -e "编号\t书名\t作者\t价格" 
  cat .book.txt 
  echo "----------------------------" 
  information 
   
} 
 
 
#下面的函数用到的查询菜单 
function search_menu 
{ 
  echo;echo "----------------------------"  
  echo -n "|";echo -e "1：\t按图书编号查询" 
  echo -n "|";echo -e "2：\t按图书书名查询" 
  echo -n "|";echo -e "3：\t按图书作者查询" 
  echo -n "|";echo -e "4：\t按图书价格查询" 
  echo -n "|";echo -e "5|q：\t退出查询系统" 
  echo;echo "----------------------------"  
 
} 
function search 
{ 
  search_menu 
  read -p "请输出你的选择：" myselect 
  case "$myselect" in 
  1) 
    read -p "请输入要查询的图书的编号：" mynumber 
    echo -e "编号\t书名\t作者\t价格\n" 
    awk &#39;$1==&#39;$mynumber&#39;{print $0}&#39; .book.txt 2>/dev/null  
               
    if [ $? -ne 0 ];then 
      echo "图书不存在" 
    fi 
    search 
    ;; 
  2) 
    read -p "请输入你要查询的书名：" mybook_name 
    echo -e "编号\t书名\t作者\t价格\n" 
    awk &#39;$2~/&#39;$mybook_name&#39;/{print $0}&#39; .book.txt 2>/dev/null 
    if [ $? -ne 0 ];then 
      echo "图书不存在" 
    fi 
    search 
    ;; 
  3) 
    read -p "请输入图书的作者：" myauthor 
    echo -e "编号\t书名\t作者\t价格\n" 
    awk &#39;$3~/&#39;$myauthor&#39;/{;print $0}&#39; .book.txt 2>/dev/null 
    if [ $? -ne 0 ];then 
      echo "图书不存在" 
    fi 
    search 
    ;; 
  4) 
    read -p "请输入图书的价格：" myprice 
    echo -e "编号\t书名\t作者\t价格\n" 
    awk &#39;$4==&#39;$myprice&#39;{print $0}&#39; .book.txt 2>/dev/null 
    if [ $? -ne 0 ];then 
      echo "图书不存在" 
    fi 
    search 
    ;; 
  5) 
    information 
    ;; 
  *) 
    information 
    ;; 
  esac 
 
} 
 
information