Scene: general command output will display in the terminal, there are times when you need to execute some commands you want to save the results to a file for subsequent analysis / statistics, we need to use this time to redirect the output techniques.
>: Covering output, it will overwrite the original file contents
>>: the additional output will not overwrite the original file contents, we will continue to add to the end of the original content
2>: error output, it will overwrite the original file contents
>> 2: Error additional output will overwrite the original file contents, we will continue to add to the end of the original content
&>: The standard output and error output jointly written to the file. Covering the original content
& >>: The standard output and error output jointly written to a file (appended to the original content)
Redirect standard input (STDIN, file descriptor 0): Default input from the keyboard, may also be input from another file or command.
Redirect standard output (STDOUT, file descriptor 1): The default output to the screen.
Redirect the error output (STDERR, file descriptor 2): The default output to the screen.
Case 1: Use the output coverage (covering original language)
[root@ken ~]# vim test [root@ken ~]# cat test this is ken [root@ken ~]# echo "this is oscar" > test [root@ken ~]# cat test this is oscar
Case 2: Using append output (the original text added)
[root@ken ~]# cat test this is oscar [root@ken ~]# echo "this is ken" >> test [root@ken ~]# cat test this is oscar this is ken
Case 3: Using the wrong output redirection
The default output will fall on the wrong output terminal
[Root @ ken ~] # cat klkl> test # output redirection can not make use of the error output into the text cat: klkl: No such file or directory [Root @ ken ~] # cat klkl 2> test # 2 need> Error output redirection [root@ken ~]# cat test cat: klkl: No such file or directory
Case 4: The standard output and error output jointly written to the file
[root@ken ~]# cat klkl &> test [root@ken ~]# cat test cat: klkl: No such file or directory
Input redirection
Function is to redirect input directly into the command file.
Case: Lines of text statistics
[root@ken ~]# wc -l < /etc/passwd 28
Pipe character
Pipe command symbol (|) is the role of the previous command is supposed to be output to the standard input data after the normal standard screen as a command.
For example, we need to count the number of lines passwd file containing the root
[root@ken ~]# cat /etc/passwd | grep "root" | wc -l 2
The output value of the search command is transmitted to the statistical commands, i.e., the original information to be output to the user list screen, and then to the wc command for further processing, and therefore need only to pipe character to put between the two commands
Tsuhaifu
For Linux operation and maintenance personnel, we sometimes encounter situations obviously a file name is on the lips but it just will not come. If you remember the beginning of a file of letters, would like to traverse to find out all files that start with the keyword, how does it work?
Wildcard is the universal symbol of matching information, such as
- An asterisk (*) on behalf of matches zero or more characters (can be 0)
- Question mark (?) Matches a single character on behalf of (single character must be present)
- Digitally [0-9] Representative matching single digit between 0 and 9 character in brackets,
- The letters in the brackets [abc] match is representative of a, b, c of any three characters in a character.
All the files beginning with sda View dev directory: Case 1
[Root @ ken ~] # ls / dev / sda * / Dev / sda / dev / sda1 / dev / sda2
Case 2: View dev directory beginning with sda, there is a character behind file
[Root @ ken ~] # ls / dev / sda? /dev/sda1 /dev/sda2
After a question mark / dev / sda will not match the
File begins with sda, back to keep numbers under View dev: Case 3
Not match sda
[Root @ ken ~] # ls / dev / sda [0-9] /dev/sda1 /dev/sda2
Case 4: View dev begin with sda, back to keep letter file
[root@ken ~]# ls /dev/sda[a-z] ls: cannot access /dev/sda[a-z]: No such file or directory
Not match any documents also match less than / dev / sda, the back to keep up with the characters must be present in order to match.
Function of Three quotes
- Single quotation marks ( ''): wherein all variables escaped as a simple string.
- Double quotes ( ""): wherein the variable attributes retained without escaping.
- Backtick ( ``): the return result executes the commands.
Case 1: single quote and no explanatory variables WYSIWYG
[root@ken ~]# age=10 [root@ken ~]# echo 'my age is $age' my age is $age
Case 2: double quotation marks, explanatory variables
[root@ken ~]# age=10 [root@ken ~]# echo "my age is $age" my age is 10
Case 3: backticks for command execution
[root@ken ~]# name=`ls /root` [root@ken ~]# echo $name 10.txt 11.txt 12.txt 13.txt 14.txt 1.txt 2.txt 3.txt 4.txt 5 =5 5.txt 6.txt 7.txt 8.txt 9.txt anaconda-ks.cfg elasticsearch-6.4.0.tar.gz elasticsearch-6.4.0.tar.gz.1 ken kenken nohup.out redis-manager-1.1 redis-manager-1.1-release.tar.gz test test1.sh test.sh
It all starts with "/"
In the Linux system, directory, character device, block device, the socket is so abstract became a file, Linux system, everything is a file. Now usually we are dealing with files, and how to find them? In the Windows operating system, you want to find a file, we have to turn into the disk partition where the file (assuming that this is the D drive), and then enter the specific directory under the partition, finally found the file. But there is no letter C / D / E / F, etc. In the Linux system, all files from the Linux system is the "root (/)" directory to start, and using tree according to the file system hierarchy standard (FHS) shaped structure to store files, and defines the purpose of the common directory. In addition, Linux system file and directory names are strictly case-sensitive. For example, root, rOOt, Root, rooT represents a different directory and file name must not contain slash (/). Linux system
File structure shown in Figure 6-1.
FHS is based on past experience numerous Linux system users and developers and summed up, is a regular user in a Linux system that must be observed when storing a file to guide us what should be saved to a file location, and tell
V The user should find the file where required. However, FHS For the user, can only be regarded as a moral constraint, some users are too lazy to comply, the file will still all over the place, and some had never even heard of it.
Linux system common directory name and the corresponding content
| Directory name |
The contents of the file should be placed |
| /boot |
Power required documents - the kernel, the boot menu and the necessary configuration files |
| /dev |
As files stored on any device with an interface |
| /etc |
Profiles |
| /home |
The user's home directory |
| /bin |
Command can also be stored in single-user mode of operation |
| /lib |
Library used at boot time, and function / bin and / sbin following command to invoke |
| /sbin |
Boot process commands needed |
| /media |
It used to mount the device file directory |
| /opt |
Placing third-party software |
| /root |
The system administrator's home directory |
| /srv |
Some network services data file directory |
| /tmp |
Anyone can use the "Share" temporary directory |
| /proc |
Virtual file system, such as system kernel, processes, external devices and network status |
| /usr/local |
User-installed software |
| /usr/sbin |
Linux system will not be used to boot the software / command / script |
| /usr/share |
Help and documentation can also be placed to share files |
| /where |
The main storage of frequently changing files, such as log |
| /lost+found | When the file system error, some of the missing pieces of the file stored here |
Vs absolute path relative path
In the Linux system, there is another important concept - path.
Path refers to how to locate a file, into the absolute path and relative path.
Refers to the absolute path from the root directory (/) began to write the file or directory name
Refers to a relative path is relative to the current path of the wording.