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Clipboard (software)
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The clipboard is a software facility that can be used for short-term data storage and/or data transfer between documents or applications, via copy and paste operations. It is most commonly a part of a GUI environment and is usually implemented as an anonymous, temporary block of memory that can be accessed from most or all programs within the environment via defined programming interfaces. A typical application accesses clipboard functionality by mapping user input (keybindings, menu selections, etc.) to these interfaces.
Basic functions
The semantics of the clipboard facility varies from one operating environment to another, and can also vary between versions of the same system.
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Encyclopedia
The clipboard is a software facility that can be used for short-term data storage and/or data transfer between documents or applications, via copy and paste operations. It is most commonly a part of a GUI environment and is usually implemented as an anonymous, temporary block of memory that can be accessed from most or all programs within the environment via defined programming interfaces. A typical application accesses clipboard functionality by mapping user input (keybindings, menu selections, etc.) to these interfaces.
Basic functions
The semantics of the clipboard facility varies from one operating environment to another, and can also vary between versions of the same system. They can sometimes be changed programmatically or by user preference. This can lead to user frustration when switching between environments with different clipboard semantics particularly as copy and paste operations often become embedded in the user's muscle memory.
Most environments support a single clipboard transaction. Each cut or copy overwrites the previous contents. Normally, paste operations copy the contents, leaving the contents available in the clipboard for further pasting operations.
Data formats
Early implementations of the clipboard stored data as plain text without meta-information such as typeface, type style or color. More recent implementations support the multiple types of data, allowing complex data structures to be stored. These range from styled text formats such as RTF or HTML, through a variety of bitmap and vector image formats to complex data types like spreadsheets and database entries.
For example cutting a range of cells in a spreadsheet and then pasting them into another sheet may preserve the underlying formulae and data, and may even translate intra-cell references, so that a "SUM(...)" calculation on a sub-range of the cells is converted to refer to the newly pasted copies of those cells.
When data is added to the clipboard by an application, it typically makes it available in as many different data formats as it can. This includes both native and simpler (or more common) formats that would have a higher chance of being recognized by a wide variety of applications. Thus, when data is pasted into another application, the format that is closest to that application's native format can be used, preserving as much of the original data as possible. In Windows in particular, the internal clipboard functionality of the operating system will automatically translate data from known advanced formats to simpler formats automatically (such as RTF to plain text, or Unicode to ANSI Text), increasing the likelihood that any given application can interpret some form of the original data.
Clipboard management
Modern GUIs often provide a clipboard manager which supports multiple cut and paste transactions. In this model the clipboard is treated as a stack or scrap book, with new cuts and copies being placed added to the top of the list of recent transactions. The standard paste operation copies the most recent transaction, while specialized pastes provide access to the other stored transactions. These managers generally also provide a window that displays the transaction history and allows the user to select earlier copies, edit them, change their format and even search amongst them.
Most environments do not save the clipboard contents to any persistent storage - when a user logs out or reboots his or her system the clipboard contents are cleared and forgotten.
Operating system-specific clipboards
Microsoft Windows
In some versions of the Microsoft Windows operating system, the contents of the clipboard can be viewed at any time by using the Clipboard Viewer (Clipbook Viewer in Windows XP and 2000) application (clipbrd.exe). It helps if you run search for this program by clicking start* then search* and type in clipbrd.exe. It should be found in windows/system32. In older versions of Windows the common practice was to open a copy of the "Notepad" or "Wordpad" editor, and paste into that. Often these operations are available from the "Edit" pull down menu and they may be available via a context menu, usually accessible by context-clicking in the window or dialog entry that is to be cut from or pasted into.
The standard Windows keybindings are:
- Ctrl-c to copy data onto the clipboard
- Ctrl-x to cut data to the clipboard
- Ctrl-v to paste data from the clipboard
alternative keybindings (available in most windows programs)
- Ctrl-Insert is copy
- Shift-Delete is cut
- Shift-Insert is paste
the advantage of the alternative keys is that the fingers can stay close to the arrow and selection keys when you are editing a large body of text
The Clipbook Viewer was removed entirely in Windows Vista.
Mac OS X
In the Macintosh Operating System the contents can be viewed by selecting the Show Clipboard menu item from the Finder's Edit menu. The standard Mac OS keybindings are:
- Command-c to copy data into the clipboard
- Command-x to cut into it
- Command-v to paste data from the clipboard.
Also available as a secondary, text-only clipboard, is an emacs-style kill-ring. This works in all applications that use standard Cocoa text boxes:
- Ctrl-k to kill from cursor to end-of-line.
- Ctrl-y to yank from kill-ring to cursor.
X Window System
The X Window System commonly used on Unix and Linux systems provides a clipboard implementation via selections. Selections are asynchronous, so data is copied and converted into the desired format only on-demand.
The usage and handling of various selections is not standardized. However most modern toolkits and desktop environments, such as GNOME or KDE, follow a widely accepted convention, outlined in the freedesktop.org specification. One selection, CLIPBOARD, is used for traditional clipboard semantics, with shortcuts similar to Windows. Another selection, PRIMARY, is an X11-specific mechanism. Data is "copied" immediately upon highlighting and pasted with the third (middle) mouse button. This is usually separate from the CLIPBOARD selection and does not change its contents.
External links
Information for developers
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