Seulgi Kim

I've been writing a series of posts about CSI Sequences, but we rarely use CSI Sequences directly. However, there is a CSI Sequence that we use unknowingly. It's the clear command that clears the screen. The clear command basically uses two types of CSI sequences. One is CSI H ( Cu rsor P osition, a.k.a CUP); it moves the cursor to the beginning of the screen. The cursor is at the top-left corner after the command ends, thanks to CUP. The second CSI Sequence is CSI 2 J ( E rase in D isplay, a.k.a. ED), which is used to clear the entire screen. Linux and Mac use these two sequences; they behave the same way up to this point. However, Linux's clear and Mac's differ in their subsequent actions. In a nutshell, Linux's clear clears the scrollback buffer, while Mac's does not. Linux's one prints CSI 3 J after the two sequences. CSI 3 J is an extension of the Escape Sequence introduced by xterm that removes lines stored in the scrollback buffer. Since be...

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 c...

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...

Since most systems, including Unix, use LF ( \n , 0x0A ) as a newline character, using of CR ( \r , 0x0D ) is quite rare. One of the few cases where CR is used in modern computers is when creating progress bars in text applications. Using CR allows for a simple implementation of progress bars in terminals. The code above draws a progress bar with # and ' '(space). For convenience, I fixed the progress bar's length at 20 characters, adding one # for every 5% increase in progress. When using CR to draw a progress bar like this, there are three points to consider. The first point is to draw the progress bar on stderr instead of stdout . One of the significant differences between stdout and stderr is that stdout buffers output rather than immediately displaying it on the screen. Typically, stdout buffers output until it encounters a newline character. Therefore, if you print a progress bar without a newline character on stdout , the screen will not be updated unti...

As I explained in the previous article , Unix-like operating systems, for instance, OS X and Linux, use LF (line feed, 0x0A , \n ) as the newline character which moves the cursor to the beginning of the next line. However, the standard-defined behavior of LF only moves the cursor down to the next line, not to the beginning of the line. This difference is acceptable if files are always accessed through operating system-dependent applications. However, Unix-like systems have no distinction between files and input/output; this difference can be problematic when file and process input/output interact. To handle this difference, a terminal emulator post-processes the output appropriately. The c_oflag in the termios structure defined by the POSIX.1 standard controls this. The c_oflag is a flag for what post-processing the terminal should perform before displaying the received characters. The most important flag in c_oflag is OPOST . This flag determines whether or not to post-pro...

When installing Linux on a computer, I always install a program called sl . This program displays a train when you execute sl . It is not a practical program but rather a program that gives you time to think when you make a typo with the commonly used ls command in the terminal. Showing a train on the screen helps you calm down and not make other mistakes when you are in a hurry to type. That's why I install this program. source: https://github.com/mtoyoda/sl The terminal is a program that receives and displays two streams, stdout, and stderr, from a program. These outputs are sequential outputs and typically flow from the top left to the bottom right. However, to draw new characters on an already-used screen, a special method is needed. This special method is called escape codes . Escape codes are a kind of promise defined in the terminal. Currently, these promises follow the standards defined in ISO 6429 . However, in the past, there was no unified consensus, and each term...