In computing, a Control keyCtrl is a modifier key which, when pressed in conjunction with another key, performs a special operation (for example, Ctrl+C). Similarly to the Shift key, the Control key rarely performs any function when pressed by itself. The Control key is located on or near the bottom left side of most keyboards (in accordance with the international standard ISO/IEC 9995-2), with many featuring an additional one at the bottom right.
On keyboards that use English abbreviations for key labeling, it is usually labeled Ctrl (Control or Ctl are sometimes used, but it is uncommon). Abbreviations in the language of the keyboard layout also are in use, e.g., the German keyboard layout uses Strg as required by the German standard DIN 2137:2012-06. There is a standardized keyboard symbol (to be used when Latin lettering is not preferred). [lower-alpha 1] This symbol is encoded in Unicode as U+2388 helm symbol⎈, but it is very rarely used.
On teletypewriters and computer terminals, holding down the Control key while pressing another key would send an ASCII C0 control character, instead of directly reporting a key press to the system. The control characters were used as non-printing characters that signal the terminal or teletypewriter to perform a special action, such as ringing a bell, ejecting a page or erasing the screen, or controlling where the next character will display.
The first 32 ASCII characters are the control characters, representable by a 5-bit binary number. Because ASCII characters were represented as 7 bits, if a key is pressed while the Control key was held down, teletypewriters and terminals would simply set the first 2 bits of a character to 0, converting the character into a control character. For example, the character "a" has a binary ASCII code of 110 0001
. This code would be converted to 000 0001
, corresponding to the ASCII character with id 1 (the SOH Character). The table at C0 and C1 control codes § C0 controls shows the ASCII control characters, with the "Caret notation" column showing a caret (^), followed by the character to press while the Control key is held down to generate the character.
If a teletypewriter or terminal is connected to a computer, the software on the computer can interpret control characters it receives however it is written to do so; a given control character can be interpreted differently from how it would be interpreted by a teletypewriter or terminal that receives it. For example, Control-C, received from a teletypewriter or terminal, is interpreted as "interrupt the current program" in some command-line interfaces, and Control-E is interpreted by the Emacs text editor as "move the editor cursor to the end of the line".
Computer keyboards directly attached to a computer, as is the case for a personal computer or workstation, distinguish each physical key from every other and report all keypresses and releases to the controlling software. This allows the software to interpret Control key combinations as it chooses, including being able to interpret a combination of the Control key, another modifier key, and a letter, number, or symbol key differently from the way it interprets a combination of the Control key and the letter, number, or symbol key without that other modifier key.
The keyboards of many early computer terminals, including the Teletype Model 33 ASR and Lear-Siegler ADM-3A, and early models of the IBM PC, positioned the Control key on the left of the keyboard, whereas caps lock resides in the same position on most modern keyboards. The traditional layout was preserved for later workstation systems and is often associated with Unix workstations. Keyboards from Sun Microsystems came in two layouts; "Unix" and "PC-style", with the Unix layout having the traditional placing of the Control key and other keys. [1] The keyboards produced for One Laptop Per Child computers also have the Control key in this location. [2] Other vendors produce keyboards for different computer systems with this placement of the Control key, such as the Happy Hacking Keyboard.
Some users of keyboards with caps lock on the left remap the keys to exchange Control and caps lock, finding the traditional location more ergonomic for using programs benefiting from use of the Control key. Keyboard layout preferences specifically to address this need are available in some operating systems.
Others leave the control key in the lower-left corner of the keyboard, and press it using the side of their palm. The choice of location for the control key often comes down to the typist's hand shape and posture.
There are several common notations for pressing the Control key in conjunction with another key. Each notation below means press and hold Ctrl while pressing the X key:
^X | Traditional caret notation |
C-x | Emacs and Vim notation |
CTRL-X | Old Microsoft notation |
Ctrl+X | Current Microsoft notation |
Ctrl/X | OpenVMS notation |
⌃X | Classic Mac OS and macOS notation, used in menus and Sticky Keys (similar to caret notation, but using U+2303⌃UP ARROWHEAD instead of a caret) [3] |
Control–X | Classic Mac OS and macOS notation, used in prose [4] |
CNTL/X | Cisco IOS notation |
|X | Bar notation |
Different application programs, user interfaces, and operating systems use the various control key combinations for different purposes.
Key combination | Microsoft Windows/KDE/GNOME | Unix (command line and programs using readline) | Emacs (if different from Unix command line) |
---|---|---|---|
Ctrl+A | Select all | Beginning of line | |
Ctrl+B | Bold | Backward one character | |
Ctrl+C | Copy | Generate SIGINT (terminate program) | Compound command |
Ctrl+D | Font window (word processing); Add to bookmarks (Browsers) | Forward delete, or if line is empty, end of input (traditional Unix) | Forward delete |
Ctrl+E | Center alignment (word processing) | End of line | |
Ctrl+F | Find (usually a small piece of text in a larger document) | Forward one character | |
Ctrl+G | Go to (line number) | Abort current operation | |
Ctrl+H | Replace; History | Delete previous character | Help key |
Ctrl+I | Italic; Incremental search | Command-line completion (same as Tab key) | |
Ctrl+J | Justify; Downloads | Line feed (LFD) | LFD (to evaluate Lisp expressions) |
Ctrl+K | Insert hyperlink (word processing) | Cut ("Kill") text between cursor and end of line | |
Ctrl+L | Create list; Left align (word processing) | Clear screen | Redraw window/terminal, and recenter view around current line |
Ctrl+M | Increase margin by 1/2 inch (word processing) | Same as Enter key | |
Ctrl+N | New (window, document, etc.) | Next line (in history) | Next line |
Ctrl+O | Open | Enter plus next line (in history) | Insert ("open") new line |
Ctrl+P | Previous line (in history) | Previous line | |
Ctrl+Q | Quit application | Resume transmission | Literal insert |
Ctrl+R | Refresh page; Right align (word processing) | Search backwards in history | Search backwards |
Ctrl+S | Save | Pause transmission | Search forward |
Ctrl+T | Open new tab | Transpose characters, display status | |
Ctrl+U | Underline; HTML of page you are currently looking at | Cut text between beginning of line and cursor | Prefix numerical argument to next command |
Ctrl+V | Paste | Literal insert | Page down |
Ctrl+W | Close window or tab | Cut previous word | Cut |
Ctrl+X | Cut | Compound command | |
Ctrl+Y | Redo | Paste | |
Ctrl+Z | Undo | Suspend program | Iconify window |
Ctrl+⇧ Shift+Z | Redo | not available | |
Ctrl+[ | Decrease font size | Same as Esc or Alt | |
Ctrl+] | Increase font size | Search for the next character typed | undefined or rarely used |
Ctrl+= | Toggle font subscript | not available | |
Ctrl+⇧ Shift+= | Toggle font superscript | not available | |
Ctrl+End | Bottom (end of document or window) | undefined or rarely used | Bottom (end of text buffer) |
Ctrl+Home | Top (start of document or window) | undefined or rarely used | Top (start of text buffer) |
Ctrl+Insert | Copy | undefined or rarely used | Copy |
Ctrl+PgDn | Next tab | undefined or rarely used | Scroll window to the right |
Ctrl+PgUp | Previous tab | undefined or rarely used | Scroll window to the left |
Ctrl+Tab ↹ | Next window or tab | not available | |
Ctrl+⇧ Shift+Tab ↹ | Previous window or tab | not available | |
Ctrl++ | Grow Screen | not available | |
Ctrl+- | Shrink Screen | Undo | |
Ctrl+/ | undefined or rarely used | Same as Ctrl+- (Undo) | |
Ctrl+\ | undefined or rarely used | Generate SIGQUIT (terminate and dump core) | undefined or rarely used |
Ctrl+← | Previous word | undefined or rarely used | Previous word |
Ctrl+→ | Next word | undefined or rarely used | Next word |
Ctrl+Delete | Delete next word | undefined or rarely used | Delete next word |
Ctrl+← Backspace | Delete previous word | undefined or rarely used | Delete previous word |
Ctrl+Alt+← Backspace | undefined or rarely used on Windows; restart X11 on Unix-like desktops | undefined or rarely used | |
Ctrl+Alt+↑ | Rotate screen right-side up | undefined or rarely used | |
Ctrl+Alt+↓ | Rotate screen upside down | undefined or rarely used | |
Ctrl+Alt+← | Rotate screen left | undefined or rarely used | |
Ctrl+Alt+→ | Rotate screen right | undefined or rarely used | |
Ctrl+⇧ Shift+Esc | Open task manager | not available | |
[[Control-Alt-Delete|Ctrl+Alt+Del]] | Reboot; Open task manager or session options | not available | |
Ctrl+Mousewheel | Scroll in/out |
In early first-person shooters, the left Ctrl key is often used to fire a weapon. In newer games, the key is often used for crouching instead. [5]
Generally, the Command key, labeled with the ⌘ symbol on Apple Macintosh computers, performs the equivalent functions in classic Mac OS and macOS applications (for example, ⌘C copies, while ⌘P prints; the same holds for saving, cutting, and pasting).
Macintoshes also have a Control key, but it has different functionality. The original Apple mouse design reduced complexity by only offering one button. As the interface developed, contextual menus were offered to access extra options. Another button was needed to access these. On Unix and Windows, the user had other mouse buttons to use. On Classic Mac OS and macOS, the Control key is used to invoke a "right-click". Apple calls this a "secondary click" as left-handers can choose which side this button is on.
ASCII, abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of technical limitations of computer systems at the time it was invented, ASCII has just 128 code points, of which only 95 are printable characters, which severely limited its scope. Modern computer systems have evolved to use Unicode, which has millions of code points, but the first 128 of these are the same as the ASCII set.
In computing and telecommunication, a control character or non-printing character (NPC) is a code point in a character set that does not represent a written character or symbol. They are used as in-band signaling to cause effects other than the addition of a symbol to the text. All other characters are mainly graphic characters, also known as printing characters, except perhaps for "space" characters. In the ASCII standard there are 33 control characters, such as code 7, BEL, which rings a terminal bell.
In telecommunication, an End-of-Transmission character (EOT) is a transmission control character. Its intended use is to indicate the conclusion of a transmission that may have included one or more texts and any associated message headings.
In computing, a modifier key is a special key on a computer keyboard that temporarily modifies the normal action of another key when pressed together. By themselves, modifier keys usually do nothing; that is, pressing any of the ⇧ Shift, Alt, or Ctrl keys alone does not (generally) trigger any action from the computer.
The null character is a control character with the value zero. It is present in many character sets, including those defined by the Baudot and ITA2 codes, ISO/IEC 646, the C0 control code, the Universal Coded Character Set, and EBCDIC. It is available in nearly all mainstream programming languages. It is often abbreviated as NUL. In 8-bit codes, it is known as a null byte.
A text box is a control element of a graphical user interface, that should enable the user to input text information to be used by a program. Human Interface Guidelines recommend a single-line text box when only one line of input is required, and a multi-line text box only if more than one line of input may be required. Non-editable text boxes can serve the purpose of simply displaying text.
In computing, a keyboard shortcut also known as hotkey is a series of one or several keys to quickly invoke a software program or perform a preprogrammed action. This action may be part of the standard functionality of the operating system or application program, or it may have been written by the user in a scripting language. Some integrated keyboards also include pointing devices; the definition of exactly what counts as a "key" sometimes differs.
The Alt keyAlt on a computer keyboard is used to change (alternate) the function of other pressed keys. Thus, the Alt key is a modifier key, used in a similar fashion to the Shift key. For example, simply pressing A will type the letter 'a', but holding down the Alt key while pressing A will cause the computer to perform an Alt+A function, which varies from program to program. The international standard ISO/IEC 9995-2 calls it Alternate key. The key is located on either side of the space bar, but in non-US PC keyboard layouts, rather than a second Alt key, there is an 'Alt Gr' key to the right of the space bar. Both placements are in accordance with ISO/IEC 9995-2. With some keyboard mappings, the right Alt key can be reconfigured to function as an AltGr key although not engraved as such.
Backspace is the keyboard key that in typewriters originally pushed the carriage one position backwards, and in modern computer systems typically moves the display cursor one position backwards, deletes the character at that position, and shifts back any text after that position by one character.
The Command key, ⌘, formerly also known as the Apple key or open Apple key, is a modifier key present on Apple keyboards. The Command key's purpose is to allow the user to enter keyboard commands in applications and in the system. An "extended" Macintosh keyboard—the most common type—has two command keys, one on each side of the space bar; some compact keyboards have one only on the left.
A bell character is a device control code originally sent to ring a small electromechanical bell on tickers and other teleprinters and teletypewriters to alert operators at the other end of the line, often of an incoming message. Though tickers punched the bell codes into their tapes, printers generally do not print a character when the bell code is received. Bell codes are usually represented by the label "BEL
". They have been used since 1870.
The Option key, ⌥, is a modifier key present on Apple keyboards. It is located between the Control key and the Command key on a typical Mac keyboard. There are two Option keys on modern Mac desktop and notebook keyboards, one on each side of the space bar.
The currency sign¤ is a character used to denote an unspecified currency. It can be described as a circle the size of a lowercase character with four short radiating arms at 45° (NE), 135° (SE), 225° (SW) and 315° (NW). It is raised slightly above the baseline. The character is sometimes called scarab.
On computer keyboards, the Esc keyEsc is a key used to generate the escape character. The escape character, when sent from the keyboard to a computer, often is interpreted by software as "stop", "cancel" or "exit", and when sent from the computer to an external device marks the beginning of an escape sequence to specify operating modes or characteristics generally.
Caret notation is a notation for control characters in ASCII. The notation assigns ^A
to control-code 1, sequentially through the alphabet to ^Z
assigned to control-code 26 (0x1A). For the control-codes outside of the range 1–26, the notation extends to the adjacent, non-alphabetic ASCII characters.
The Fn key, short form for function, is a modifier key on many keyboards, especially on laptops, used in a compact layout to combine keys which are usually kept separate. It is typically found on laptops due to their keyboard size restrictions. It is also found on many full-sized "multimedia" keyboards as the F-Lock key. It is mainly for the purpose of changing display or audio settings quickly, such as brightness, contrast, or volume, and is held down in conjunction with the appropriate key to change the settings.
On personal computers with numeric keypads that use Microsoft operating systems, such as Windows, many characters that do not have a dedicated key combination on the keyboard may nevertheless be entered using the Alt code. This is done by pressing and holding the Alt key, then typing a number on the keyboard's numeric keypad that identifies the character and then releasing Alt.
Control-C is a common computer command. It is generated by pressing the C key while holding down the Ctrl key on most computer keyboards.
Super key (❖) is an alternative and older name for what is commonly labelled as the Windows key or Command key on modern keyboards, typically bound and handled as such by Linux and BSD operating systems and software today.
A keyboard layout is any specific physical, visual or functional arrangement of the keys, legends, or key-meaning associations (respectively) of a computer keyboard, mobile phone, or other computer-controlled typographic keyboard.
Esc | F1 | F2 | F3 | F4 | F5 | F6 | F7 | F8 | F9 | F10 | F11 | F12 | PrtScn/ SysRq | Scroll Lock | Pause/ Break | |||||||||
![]() | Insert | Home | PgUp | Num Lock | ∕ | ∗ | − | |||||||||||||||||
Delete | End | PgDn | 7 | 8 | 9 | + | ||||||||||||||||||
4 | 5 | 6 | ||||||||||||||||||||||
↑ | 1 | 2 | 3 | Enter | ||||||||||||||||||||
← | ↓ | → | 0 Ins | . Del |