1、if的语法结构if 职邗珩垃[ condition ]then statements[elif condition then statements. ..][else statements ]fi
2、整数比较
3、字符串比较
4、权限判断，用于判断文件对当前用于的权限-r 有读的权限-w 有写的权限-x 有执行的权限
5、if对于文件的判断
6、脚本实例脚本一：#!/bin/shecho "挢旗扦渌;Please input a integer:"rea颊俄岿髭d integer1if [ "$integer1" -lt 30 ]then echo "The integer which you input is lower than 30."fi脚本二：if [ -f 023.txt ];then echo "file is exist"else touch 023.txtfi