Shell编程 - 判断篇

1. 字符串比较符

需要注意的是，使用-z或-n判断字符串长度时，变量要加双引号。⭐

# 加了双引号才能正常判断是否为空
# [ -z "$a" ] && echo yes || echo no
yes
# [ -n "$a" ] && echo yes || echo no
no
# 使用了双中括号就不用了双引号
# [[ -n $a ]] && echo yes || echo no
no
# [[ -z $a ]] && echo yes || echo no
yes

2. 文件测试

案例1. 检查指定的文件（目录，软链接）脚本，如果文件存在则显示文件名字，大小，权限，硬链接数，所属用户和用户组，文件修改时间。如果文件不存在则输出文件不存在。⭐⭐⭐

#1.vars
thing=$1
#2.判断参数
if [ $# -eq 0 ];then
	echo "HELP：$0 + 参数"
	exit
fi

#3.判断
  #目录
if [ -d $thing ];then
	echo "$thing is a dir"
        echo "目录大小：`du -sh $thing|awk '{print $1}'`"
        echo "目录权限：`ls -ld $thing|awk '{print $1}'|sed -r 's#^.##g'`/`stat $thing|awk -F '[(/]' 'NR==4{print $2}'`"
        echo "硬链接数：`ls -ld $thing|awk '{print $2}'`"
        echo "所属用户：`ls -ld $thing|awk '{print $3}'`"
        echo "所属用户组:`ls -ld $thing|awk '{print $4}'`"
        echo "修改时间:`ls -ld $thing|awk '{print $6,$7,$8}'`"
	exit 
fi

#软链接
  [ -L $thing ] && {
     echo $thing is a soft_link
        echo "文件大小：`ls -l $thing|awk '{print $5}'`"
        echo "权限：`ls -l $thing|awk '{print $1}'|sed -r 's#^.##g'`/`stat $thing|awk -F '[(
/]' 'NR==4{print $2}'`"
        echo "硬链接数：`ls -l $thing|awk '{print $2}'`"
        echo "所属用户：`ls -l $thing|awk '{print $3}'`"
        echo "所属用户组:`ls -l $thing|awk '{print $4}'`"
        echo "修改时间:`ls -l $thing|awk '{print $6,$7,$8}'`"
     exit 0
       }


  #文件
if [ -f $thing ];then
  echo "$thing is a file"
	if [ -x $thing ];then
		echo "该文件有执行权限"
	else
		echo "该文件没有执行权限"
	fi
	echo "文件大小：`ls -l $thing|awk '{print $5}'`"
        echo "权限：`ls -l $thing|awk '{print $1}'|sed -r 's#^.##g'`/`stat $thing|awk -F '[(
/]' 'NR==4{print $2}'`"
        echo "硬链接数：`ls -l $thing|awk '{print $2}'`"
        echo "所属用户：`ls -l $thing|awk '{print $3}'`"
        echo "所属用户组:`ls -l $thing|awk '{print $4}'`"
        echo "修改时间:`ls -l $thing|awk '{print $6,$7,$8}'`"

else
	echo "$thing dose not exist"
fi

3. 布尔运算符

4. 逻辑判断符