Incomputing, aControl keyCtrl is amodifier key which, when pressed in conjunction with another key, performs a special operation (for example,Ctrl+C). Similarly to theShift 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 standardISO/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 labeledCtrl (Control orCtl are sometimes used, but it is uncommon). Abbreviations in the language of the keyboard layout also are in use, e.g., theGerman keyboard layout usesStrg (Steuerung) as required by the German standardDIN 2137:2012-06. There is a standardized keyboard symbol (to be used when Latin lettering is not preferred).[a] This symbol is encoded inUnicode asU+2388helm symbol⎈, but it is very rarely used.
Onteletypewriters andcomputer terminals, holding down the Control key while pressing another key would send anASCIIC0 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 charactera has a binary ASCII code of110 0001. This code would be converted to000 0001, corresponding to the ASCII character with id 1 (the SOH Character). The table atC0 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 somecommand-line interfaces, and Control-E is interpreted by theEmacs 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 apersonal computer orworkstation, 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, anothermodifier 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 earlycomputer terminals, including theTeletype Model 33 ASR andLear-SieglerADM-3A, and early models of theIBM PC, positioned the Control key on the left of the keyboard, whereascaps lock resides in the same position on most modern keyboards. The traditional layout was preserved for laterworkstation systems and is often associated withUnix workstations. Keyboards fromSun 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 forOne 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 theHappy 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 holdCtrl while pressing theX key:
| ^X | Traditionalcaret notation |
| C-x | Emacs andVim notation |
| CTRL-X | OldMicrosoft notation |
| Ctrl+X | Current Microsoft notation |
| Ctrl/X | OpenVMS notation |
| ⌃X | Classic Mac OS andmacOS notation, used in menus andSticky Keys (similar to caret notation, but usingU+2303 ⌃UP ARROWHEAD instead of acaret)[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 usingreadline) | Emacs (if different from Unix command line) |
|---|---|---|---|
| Ctrl+A | Select all | Beginning of line | |
| Ctrl+B | Bold | Backward one character | |
| Ctrl+C | Copy | GenerateSIGINT (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); Finds the next occurrence of a previously searched term (Browsers) | Abort current operation | |
| Ctrl+H | Replace; History | Delete previous character | Help key |
| Ctrl+I | Italic; Incremental search | Command-line completion (same asTab key) | |
| Ctrl+J | Justify; Downloads | Line feed (LFD) | LFD (to evaluateLisp 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 asEnter 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 | Print current page | 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, displaystatus | |
| 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 | Iconifywindow |
| Ctrl+⇧ Shift+Z | Redo | not available | |
| Ctrl+[ | Decrease font size | Same asEsc orAlt | |
| 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 orwindow) | undefined or rarely used | Bottom (end of text buffer) |
| Ctrl+Home | Top (start of document orwindow) | undefined or rarely used | Top (start of text buffer) |
| Ctrl+Insert | Copy | undefined or rarely used | Copy |
| Ctrl+PgDn | Nexttab | undefined or rarely used | Scroll window to the right |
| Ctrl+PgUp | Previoustab | undefined or rarely used | Scroll window to the left |
| Ctrl+Tab ↹ | Nextwindow ortab | not available | |
| Ctrl+⇧ Shift+Tab ↹ | Previouswindow ortab | not available | |
| Ctrl++ | Zoom in onwindow | not available | |
| Ctrl+- | Zoom out onwindow | Undo | |
| Ctrl+0 | Restorewindow to defaultzoom factor | not available | |
| Ctrl+/ | undefined or rarely used | Same asCtrl+- (Undo) | |
| Ctrl+\ | undefined or rarely used | GenerateSIGQUIT (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+Del | 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; restartX11 onUnix-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 | |
| Ctrl+Alt+Del | Reboot; Open task manager or session options | not available | |
| Ctrl+Mousewheel | Zoom in/out | ||
In earlyfirst-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, theCommand key, labeled with the ⌘ symbol onApple Macintosh computers, performs the equivalent functions inclassic Mac OS andmacOS applications (for example,⌘C copies, while⌘P prints; the same holds for saving, cutting, and pasting).
Mac computers 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.
| 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 | ||||||||||||||||||||