Shell学习之条件测试(四)
Shell学习之条件测试
目录
逻辑测试
文件测试
数值比较
字符串比较
逻辑测试
格式: [ 表达式 ] 操作符 [ 表达式2 ] …… 命令1 操作符 命令2 …… 常用的操作符 ( 注意:-a和-o放在[]里面用,&&和||放在[]外面用 ) -a 或 && 逻辑与 -o 或 || 逻辑或 ! 逻辑否
文件测试
文件测试 格式1: [ 操作符 文件或目录 ] 格式2:test 操作符 文件或目录 常用的测试操作符 -d :测试是否为目录( Directory ) -e :测试目录或文件是否存在(Exist) -f :测试是否为文件(File) -r :测试当前用户是否可读(read) -w:测试当前用户是否可写(write) -x :测试当前用户是否可执行(excute)
例子:备份Mysql数据库,业务代码没有完善
#/bin/bash back_dir=/var/mysql_back if !test -d $back_dir;then mkdir -p $back_dir fi echo "开始备份"
数值比较
格式1:[ 整数1 操作符 整数2 ] 格式2: test 整数1 操作符 整数2 常用的测试操作符 -eq : 等于 (Equal) -ne : 不等于 (Not Equal) -gt : 大于(Greater Than) -lt : 小于 (Lesser Than) -le : 小于或等于(Lesser or Equal) -ge : 大于或等于(Greater or Equal)
例子
#/bin/bash if [ $UID -ne 0];then echo "没有权限" exit fi yum -y install httpd
字符串比较
格式1:[ 字符串1 = 字符串2 ] [ 字符串1 != 字符串2 ] 格式2:[ -z 字符串 ] 常用的测试操作符 = : 字符串内容相同 != : 字符串内容不同 -z : 字符串内容为空
例子
#/bin/bash if [ $USER = "root"];then yum -y install httpd fi echo "没有权限" exit
所有表达式
( EXPRESSION ) EXPRESSION is true ! EXPRESSION EXPRESSION is false EXPRESSION1 -a EXPRESSION2 both EXPRESSION1 and EXPRESSION2 are true EXPRESSION1 -o EXPRESSION2 either EXPRESSION1 or EXPRESSION2 is true -n STRING the length of STRING is nonzero STRING equivalent to -n STRING -z STRING the length of STRING is zero STRING1 = STRING2 the strings are equal STRING1 != STRING2 the strings are not equal INTEGER1 -eq INTEGER2 INTEGER1 is equal to INTEGER2 INTEGER1 -ge INTEGER2 INTEGER1 is greater than or equal to INTEGER2 INTEGER1 -gt INTEGER2 INTEGER1 is greater than INTEGER2 INTEGER1 -le INTEGER2 INTEGER1 is less than or equal to INTEGER2 INTEGER1 -lt INTEGER2 INTEGER1 is less than INTEGER2 INTEGER1 -ne INTEGER2 INTEGER1 is not equal to INTEGER2 FILE1 -ef FILE2 FILE1 and FILE2 have the same device and inode numbers FILE1 -nt FILE2 FILE1 is newer (modification date) than FILE2 FILE1 -ot FILE2 FILE1 is older than FILE2 -b FILE FILE exists and is block special -c FILE FILE exists and is character special -d FILE FILE exists and is a directory -e FILE FILE exists -f FILE FILE exists and is a regular file -g FILE FILE exists and is set-group-ID -G FILE FILE exists and is owned by the effective group ID -h FILE FILE exists and is a symbolic link (same as -L) -k FILE FILE exists and has its sticky bit set -L FILE FILE exists and is a symbolic link (same as -h) -O FILE FILE exists and is owned by the effective user ID -p FILE FILE exists and is a named pipe -r FILE FILE exists and read permission is granted -s FILE FILE exists and has a size greater than zero -S FILE FILE exists and is a socket -t FD file descriptor FD is opened on a terminal -u FILE FILE exists and its set-user-ID bit is set -w FILE FILE exists and write permission is granted -x FILE FILE exists and execute (or search) permission is granted