查看所有的Shell变量:[root@szm ~]# set
查看所有预定义Shell变量:[root@szm ~]# env
%d:整数 %s:字符串 \n:回车换行 \r:只回车 \t:水平制表符 \v:垂直制表符 |
运算:
1)表达式必须置于$[]内
2)数字与运算符之间应当有一个空格
[root@szm bash]# cat a1.sh
#!/bin/bash
a=$[ 3+2 ]
echo "a="$a
b=$[ 3+2*25/3-1 ]
echo "b="$b
-gt:大于 -lt:小于 -eq:等于 -ne:不等于 -ge:大于等于 -le:小于等于 |
-a file True if file exists.
-b file True if file exists and is a block special file.
-c file True if file exists and is a character special file.
-d file True if file exists and is a directory.
-e file True if file exists.
-f file True if file exists and is a regular file.
-g file True if file exists and is set-group-id.
-h file True if file exists and is a symbolic link.
-k file True if file exists and its ‘‘sticky’’ bit is set.
-p file True if file exists and is a named pipe (FIFO).
-r file True if file exists and is readable.
-s file True if file exists and has a size greater than zero.
-t fd True if file descriptor fd is open and refers to a terminal.
-u file True if file exists and its set-user-id bit is set.
-w file True if file exists and is writable.
-x file True if file exists and is executable.
-O file True if file exists and is owned by the effective user id.
-G file True if file exists and is owned by the effective group id.
-L file True if file exists and is a symbolic link.
-S file True if file exists and is a socket.
-N file True if file exists and has been modified since it was last read.
file1 -nt file2 True if file1 is newer (according to modification date) than file2, or if file1 exists and file2 does not.
file1 -ot file2
True if file1 is older than file2, or if file2 exists and file1 does not.
file1 -ef file2
True if file1 and file2 refer to the same device and inode numbers.