Shell学习之条件测试
目录
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