UNIX Tutorial Three
2015-08-20 17:56
253 查看
UNIX Tutorial Three
http://www.ee.surrey.ac.uk/Teaching/Unix/unix3.html3.1 Redirection
Most processes initiated by UNIX commands write to the standard output (that is, they write to the terminal screen), and many take their input from the standard input (that is, they read it from the keyboard). There is also the standard error, where processeswrite their error messages, by default, to the terminal screen.
We have already seen one use of the cat command to write the contents of a file to the screen.
Now type cat without specifing a file to read
% cat
Then type a few words on the keyboard and press the [Return] key.
Finally hold the [Ctrl] key down and press [d] (written as
^D for short) to end the input.
What has happened?
If you run the cat command without specifing a file to read, it reads the standard input (the keyboard), and on receiving the 'end of file' (^D), copies it to the standard output (the screen).
In UNIX, we can redirect both the input and the output of commands.
3.2 Redirecting the Output
We use the > symbol to redirect the output of a command. For example, to create a file calledlist1 containing a list of fruit, type
% cat > list1
Then type in the names of some fruit. Press [Return] after each one.
pear
banana
apple
^D {this means press [Ctrl] and [d] to stop}
What happens is the cat command reads the standard input (the keyboard) and the > redirects the output, which normally goes to the screen, into a file called
list1
To read the contents of the file, type
% cat list1
Exercise 3a
Using the above method, create another file called list2 containing the following fruit: orange, plum, mango, grapefruit. Read the contents oflist2
3.2.1 Appending to a file
The form >> appends standard output to a file. So to add more items to the filelist1, type
% cat >> list1
Then type in the names of more fruit
peach
grape
orange
^D (Control D to stop)
To read the contents of the file, type
% cat list1
You should now have two files. One contains six fruit, the other contains four fruit.
We will now use the cat command to join (concatenate)
list1 and list2 into a new file called
biglist. Type
% cat list1 list2 > biglist
What this is doing is reading the contents of list1 and
list2 in turn, then outputing the text to the file biglist
To read the contents of the new file, type
% cat biglist
3.3 Redirecting the Input
We use the < symbol to redirect the input of a command.The command sort alphabetically or numerically sorts a list. Type
% sort
Then type in the names of some animals. Press [Return] after each one.
dog
cat
bird
ape
^D (control d to stop)
The output will be
ape
bird
cat
dog
Using < you can redirect the input to come from a file rather than the keyboard. For example, to sort the list of fruit, type
% sort < biglist
and the sorted list will be output to the screen.
To output the sorted list to a file, type,
% sort < biglist > slist
Use cat to read the contents of the file
slist
3.4 Pipes
To see who is on the system with you, type% who
One method to get a sorted list of names is to type,
% who > names.txt
% sort < names.txt
This is a bit slow and you have to remember to remove the temporary file called names when you have finished. What you really want to do is connect the output of the who command directly to the input of the sort command. This is exactly what pipes do.
The symbol for a pipe is the vertical bar |
For example, typing
% who | sort
will give the same result as above, but quicker and cleaner.
To find out how many users are logged on, type
% who | wc -l
Exercise 3b
Using pipes, display all lines oflist1 and list2 containing the letter 'p', and sort the result.
% cat list1 list2 | grep p | sort
Summary
Command | Meaning |
---|---|
command > file | redirect standard output to a file |
command >> file | append standard output to a file |
command < file | redirect standard input from a file |
command1 | command2 | pipe the output of command1 to the input of command2 |
cat file1 file2 > file0 | concatenate file1 and file2 to file0 |
sort | sort data |
who | list users currently logged in |
相关文章推荐
- Win 10打击盗版软件的具体方式
- Handler引起的内存泄露问题
- 欢迎使用CSDN-markdown编辑器
- django报错:ImproperlyConfigured和AppRegistryNotReady
- IllegalArgumentException:The observer is null的解决方法
- 设计模式笔记(四)--工厂方法模式、抽象工厂模式
- 使用 Linux 系统调用的内核命令
- C++常见错误及解决方法,持续更新
- 如何给MP4视频加字幕
- Hadoop RCFile存储格式详解(源码分析、代码示例)
- SQL Server 跨网段(跨机房)复制
- 解决Android软键盘弹出引起的各种不适
- MySQL清空表数据并重置Auto_increment字段起始值为1
- 后端分布式系列:分布式存储-概述
- 分布式存储概述
- graphite
- js/jquery 去掉空格.回车.换行
- 多个线程调用同一个处理函数的互斥问题
- Windows 10企业批量部署实战之Logs日志存放
- Windows 10企业批量部署实战之Logs日志存放