Skip to main content

Clear Screen with CSI Sequence

Today, following my previous post, I will explain how to clear the screen using CSI Sequences. There are two sequences in the CSI Sequence for clearing.

The first one is the Erase in Line sequence, called EL. It is composed of CSI # K; it is used to erase lines, as the name suggests. If the # is not provided, the default value is 0, and if a value is provided, it must be one of the three: 0, 1, or 2. The terminal will ignore the sequence if any other value is provided. For example, if you print 0x311b5b334b32(or 1^[3K2), the terminal ignores ^[3K, and the screen displays only 12. The behavior of 0, 1, and 2 can be summarized as follows.

0
Erases from the cursor to the end of the line.
1
Erases from the beginning of the line to the cursor.
2
Erases the entire line, regardless of the cursor's position.

Remember that the EL sequence does not move the cursor's position. Therefore, if you want to erase the current line and write a new line on the current line, you should use the EL sequence together with a carriage return (\r).

The second is the Erase in Display sequence, called ED. It is composed of CSI # J and is used to erase the screen. Like EL, the area of the screen to be erased is determined by the value of #.

0
Erases from the cursor to the end of the screen.
1
Erases from the beginning of the screen to the cursor.
2
Erases the entire screen, regardless of the cursor's position.
3
Erases the lines stored in the scroll buffer.

As you see, it is the same as EL. The default value is 0, not moving the cursor's position, and ignoring values other than the defined values. The only difference is the number 3, which is not defined in EL.

This sequence is used to erase the values stored in the scrollback buffer. It had not existed in the VT100 specification. At that time, terminals did not have the concept of scrolling. This sequence was added after the appearance of the xterm terminal emulator, which came with the X Window System. So, in the past, many terminal emulators did not support it, but nowadays most environments support CSI 3 J without any problems.

ED and EL are rarely used directly unless you are a fan of a TUI. It is because these sequences are fundamentally for controlling the terminal, and the purpose of most programs we write is not to control the terminal. However, we use ED every day without realizing it. In the next post, we will take a closer look at this topic.

Labels:

Comments

Post a Comment

Popular posts from this blog

[C++] Handling Exceptions in Constructors

When you use RAII idiom, there are often situations where constructors have to do complex tasks. These complex tasks can sometimes fail, resulting in throwing exceptions. This raises a concern: Is it okay to throw exceptions in constructors? The first concern is memory leaks. Fortunately, memory leaks do not occur. Variables created on the stack are released through stack unwinding, and if an exception occurs during heap allocation with the new operator, the new operator automatically deallocates the memory and returns nullptr . The next concern is whether the destructor of the member variables will be called correctly. However, this is also not a problem. When an exception occurs, member variables can be divided into three categories: fully initialized member variables, member variables being initialized, and uninitialized member variables. Fully initialized member variables have had their constructors called and memory allocations completed successfully. In the example code, t...
Post a Comment
Read more

Iterator Adapters in Rust

An Iterator that takes another iterator and returns a new one is called an iterator adapter . The name "adapter" comes from one of the GoF's design patterns, the adapter pattern . However, in reality, it corresponds more to the decorator pattern , so if you pay too much attention to the name, you might get confused about its purpose. So it's better not to worry too much about the name. Enough complaining about the name, what does an iterator adapter do? An iterator adapter adds a task to be performed when the iterator iterates. This will be easier to understand when you see an example. The map function is one of the famous adapters. The iterator returned by the map function for those who have used functional languages iterates over new values transformed from the original values. Besides, various adapters are already implemented in the standard library. Among them, the most frequently used are those that are convenient to use with loops. Examples include the ...
Post a Comment
Read more