![]() They can also run in non interactive mode, via script which contains a sequence of commands.īash, Zsh, Fish and sh are all different flavors of shells. It also controls programs execution (feature called job control): kills them (CTRL + C), suspends them (CTRL + Z), sets them to run in the foreground (fg) or in the background (bg). A shell manages the user–system interaction by prompting users for input, interpreting their input, and then handling an output from the underlying operating system (much like a read–eval–print loop, REPL).įor example, if the input is 'cat file | grep hello', bash will interpret that and figure it needs to run the program cat passing 'file' as parameter and pipe the output to grep. Shells are user space applications that use the kernel API in just the same way as it is used by other application programs. Gotcha: The words terminal and TTY device are basically interchangeable as they mean the same thing The foreground process is a computer program called Shell. The whole stack as defined above is called a TTY device. As a user, you can execute several processes in parallel, but only interact with one at a time, letting the others working (or waiting) in the background. When enter is pressed, the buffered data is passed to the foreground process for the session associated with the TTY. It is also responsible to buffer the characters. The line discipline is in charge of converting special characters (like end of line, backspaces), and echoing what has been received back to the teletype, so that the user can see what it has been typed (line disciplines will be discussed in the next post of the series). DIFFERENCES BETWEEN XTERM AND PTERM DRIVERThe sequence of characters is passed to TTY driver which applies the line discipline. The computer has an UART driver to read for the hardware device. DIFFERENCES BETWEEN XTERM AND PTERM SERIALThese cables are connected to the computer through a serial cable plugged into a Universal Asynchronous Receiver and Transmitter (UART). To understand how a modern Terminal works we need to dwell just a bit on how teletypes used to work.Įach machine is connected via two cables: one to send instructions to the computer and one to receive output from the computer. The machines would provide a user interface to early mainframe computers and minicomputers, sending typed data to the computer and printing the response.īy ArnoldReinhold - Own work, CC BY-SA 3.0, Link The commercial name for this type of device is teletypewriter, Teletype or TTY (remember this word as it will come upĪgain later). read from the second line and print them on a sheet of paper.send the keystrokes down the first line.It is connected to another device (like a computer) via two logical channels, and all it does is: Generally speaking a terminal is a relatively dumb electromechanical device with an input interface (like a keyboard) and an output interface (like a display or sheet of paper). build a simple remote terminal application using golang.answer what happens when we press a key in a Terminal (like Xterm, etc.).know the difference between TTY, PTY and Shell.describe the main components in the terminal subsystem.By the end of the two articles, we should be able to: This is the first of two articles about Linux terminals. ![]()
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