Skip to main content

Understanding Escape Codes and Control Sequences

The exact term of escape code defined in ISO 6429 is a control function. Escape code is commonly used to refer to the code or sequence that represents control functions. Control codes defined by ISO 6429 are divided into two categories; C0 codes and C1 codes.

C0 codes correspond to non-printing characters in ASCII. These codes are familiar to developers. It includes line feed (\n), carriage return (\r), tab (\t), and null character (\0).

There are 32 codes in C1. They are represented by one-byte values between 0x80 and 0x9F. Unlike C0 codes, C1 codes are not defined in ASCII. They can only be used in terminals that support ASCII. In other words, they are available in 7-bit environments. In modern 8-bit environments, C1 codes cannot be used directly and must be expressed as escape sequences. Therefore, most modern terminals use escape sequences to represent C1 codes when needed.

An escape sequence is a series of characters that begins with ESC (0x1B). Sequences that correspond to C1 codes consist of a first byte of ESC (0x1B) and a second byte from @ (0x40) to _ (0x5F). For example, in a 7-bit environment, IND is represented by 0x84, but in an 8-bit environment, it is represented by ESC D (0x1B 0x44). This second byte is called the "Final character of Escape sequence," or "Fe," and two-byte C1 codes are also referred to as "Fe sequences."

In addition to Fe sequences, ISO 6429 defines other escape sequences. For example, values between `(0x60) and ~(0x7E) are called "Fs," and sequences of ESC and Fs are called "Fs sequences." Unlike C1 codes, Fs sequences are always expressed as escape sequences, regardless of the environment; they are called "independent control functions."

Fe sequences and Fs sequences mostly provide commands for controlling terminal devices. As a result, they are rarely used in modern terminal emulators. Instead, control sequences that begin with CSI (Control Sequence Introducer) are mainly used.

CSI is a value defined in the C1 control code. In a 7-bit environment, it is represented by 0x9B; in an 8-bit environment, CSI is represented by ESC [ (0x1B 0x5B). A series of sequences from CSI to byte between @ (0x40) and ~ (0x7E) are called "control sequences," and they can adjust various aspects of terminals, such as font, color, and cursor position. We will discuss this in more detail in the next article.

Labels:

Comments

Post a Comment

Popular posts from this blog

Understanding Aspect-Oriented Programming with Python Examples

Object-Oriented Programming (OOP) manages code by grouping it into independent modules known as objects, emphasizing the crucial principle of Separation of Concerns. This means each object should focus on its specific responsibilities. However, real-world applications often feature functionalities that are common across multiple objects or modules, such as logging, security, transaction management, and performance monitoring. These functionalities are called Cross-cutting Concerns. Challenge of Cross-Cutting Concerns Scattering These cross-cutting concerns, when handled solely with OOP, create two major problems. The first problem is Scattering , which is when code for a specific functionality is spread across multiple places through copying and pasting. For instance, imagine adding user permission checks and logging code to every function. The same logging and permission checking code would repeatedly appear within each method. Tangling The other issue is Tangling . This refe...
Post a Comment
Read more

Cursor Movement with CSI Sequences

Code Abbr Name CSI # A CUU CUrsor Up CSI # B CUD CUrsor Down CSI # C CUF CUrsor Forward CSI # D CUB CUrsor Backward CSI # E CNL CUrsor Next Line CSI # F CPL CUrsor Previous Line CSI # I CHT Cursor Horizontal forward Tabulation CSI # Z CBT Cursor Backward Tabulation CSI # G CHA Cursor Horizontal Absolute CSI # ; # H CUP CUrsor Position Today, we will continue from the  previous article to explore how to move the cursor using CSI sequences. The types of CSI sequences for moving the cursor can be summarized as follows. CUU, CUD, CUF, CUB These are the abbreviations for CUrsor Up, CUrsor Down, CUrsor Forward, and CUrsor Backward; as the names suggest, they move the cursor up, down, forward, and backward. They take a single number as an argument; if the argument is omitted, it is treated as 1. Thus, 0x1b[A is equivalent to 0x1b[1A . In this case, CUF and CUB move only within the same line. In other words, CUB rece...
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