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This is Info file ../info/emacs, produced by Makeinfo-1.63 from the input file emacs.texi. File: emacs, Node: Copying, Next: Intro, Prev: Distrib, Up: Top GNU GENERAL PUBLIC LICENSE ************************** Version 2, June 1991 Copyright (C) 1989, 1991 Free Software Foundation, Inc. 675 Mass Ave, Cambridge, MA 02139, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. Preamble ======== The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too. When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things. To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it. For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights. We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software. Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations. Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all. The precise terms and conditions for copying, distribution and modification follow. TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The "Program", below, refers to any such program or work, and a "work based on the Program" means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term "modification".) Each licensee is addressed as "you". Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does. 1. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program. You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee. 2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions: a. You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change. b. You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License. c. If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.) These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it. Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program. In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License. 3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following: a. Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, b. Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, c. Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.) The source code for a work means the preferred form of the work for making modifications to it. 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Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance. 5. You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it. 6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License. 7. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program. If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances. It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice. This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License. 8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License. 9. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and "any later version", you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation. 10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally. NO WARRANTY 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. END OF TERMS AND CONDITIONS How to Apply These Terms to Your New Programs ============================================= If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found. ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES. Copyright (C) 19YY NAME OF AUTHOR This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. Also add information on how to contact you by electronic and paper mail. If the program is interactive, make it output a short notice like this when it starts in an interactive mode: Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program. You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names: Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. SIGNATURE OF TY COON, 1 April 1989 Ty Coon, President of Vice This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License. File: emacs, Node: Intro, Next: Glossary, Prev: Copying, Up: Top Introduction ************ You are reading about GNU Emacs, the GNU incarnation of the advanced, self-documenting, customizable, extensible real-time display editor Emacs. (The `G' in `GNU' is not silent.) We say that Emacs is a "display" editor because normally the text being edited is visible on the screen and is updated automatically as you type your commands. *Note Display: Screen. We call it a "real-time" editor because the display is updated very frequently, usually after each character or pair of characters you type. This minimizes the amount of information you must keep in your head as you edit. *Note Real-time: Basic. We call Emacs advanced because it provides facilities that go beyond simple insertion and deletion: controlling subprocesses; automatic indentation of programs; viewing two or more files at once; editing formatted text; and dealing in terms of characters, words, lines, sentences, paragraphs, and pages, as well as expressions and comments in several different programming languages. "Self-documenting" means that at any time you can type a special character, `Control-h', to find out what your options are. You can also use it to find out what any command does, or to find all the commands that pertain to a topic. *Note Help::. "Customizable" means that you can change the definitions of Emacs commands in little ways. For example, if you use a programming language in which comments start with `<**' and end with `**>', you can tell the Emacs comment manipulation commands to use those strings (*note Comments::.). Another sort of customization is rearrangement of the command set. For example, if you prefer the four basic cursor motion commands (up, down, left and right) on keys in a diamond pattern on the keyboard, you can rebind the keys that way. *Note Customization::. "Extensible" means that you can go beyond simple customization and write entirely new commands, programs in the Lisp language to be run by Emacs's own Lisp interpreter. Emacs is an "on-line extensible" system, which means that it is divided into many functions that call each other, any of which can be redefined in the middle of an editing session. Almost any part of Emacs can be replaced without making a separate copy of all of Emacs. Most of the editing commands of Emacs are written in Lisp already; the few exceptions could have been written in Lisp but are written in C for efficiency. Although only a programmer can write an extension, anybody can use it afterward. When run under the X Window System, Emacs provides its own menus and convenient bindings to mouse buttons. But Emacs can provide many of the benefits of a window system on a text-only terminal. For instance, you can look at or edit several files at once, move text between them, and edit files at the same time as you run shell commands. File: emacs, Node: Screen, Next: User Input, Prev: Acknowledgments, Up: Top The Organization of the Screen ****************************** On a text-only terminal, the Emacs display occupies the whole screen. On the X Window System, Emacs creates its own X windows to use. We use the term "frame" to mean an entire text-only screen or an entire X window used by Emacs. Emacs uses both kinds of frames in the same way to display your editing. Emacs normally starts out with just one frame, but you can create additional frames if you wish. *Note Frames::. When you start Emacs, the entire frame except for the last line is devoted to the text you are editing. This area is called "window". The last line is a special "echo area" or "minibuffer window" where prompts appear and where you can enter responses. You can subdivide the large text window horizontally or vertically into multiple text windows, each of which can be used for a different file (*note Windows::.). In this manual, the word "window" always refers to the subdivisions of a frame within Emacs. The window that the cursor is in is the "selected window", in which editing takes place. Most Emacs commands implicitly apply to the text in the selected window (though mouse commands generally operate on whatever window you click them in, whether selected or not). The other windows display text for reference only, unless/until you select them. If you use multiple frames under the X Window System, then giving the input focus to a particular frame selects a window in that frame. Each window's last line is a "mode line" which describes what is going on in that window. It appears in inverse video if the terminal supports that, and contains text that starts like `-----Emacs: SOMETHING'. Its purpose is to indicate what buffer is being displayed above it in the window; what major and minor modes are in use; and whether the buffer contains unsaved changes. * Menu: * Point:: The place in the text where editing commands operate. * Echo Area:: Short messages appear at the bottom of the screen. * Mode Line:: Interpreting the mode line. File: emacs, Node: Point, Next: Echo Area, Up: Screen Point ===== Within Emacs, the terminal's cursor shows the location at which editing commands will take effect. This location is called "point". Many Emacs commands move point through the text, so that you can edit at different places in it. You can also place point by clicking mouse button 1. While the cursor appears to point AT a character, you should think of point as BETWEEN two characters; it points BEFORE the character that appears under the cursor. For example, if your text looks like `frob' with the cursor over the `b', then point is between the `o' and the `b'. If you insert the character `!' at that position, the result is `fro!b', with point between the `!' and the `b'. Thus, the cursor remains over the `b', as before. Sometimes people speak of "the cursor" when they mean "point", or speak of commands that move point as "cursor motion" commands. Terminals have only one cursor, and when output is in progress it must appear where the typing is being done. This does not mean that point is moving. It is only that Emacs has no way to show you the location of point except when the terminal is idle. If you are editing several files in Emacs, each in its own buffer, each buffer has its own point location. A buffer that is not currently displayed remembers where point is in case you display it again later. When there are multiple windows in a frame, each window has its own point location. The cursor shows the location of point in the selected window. This also is how you can tell which window is selected. If the same buffer appears in more than one window, each window has its own position for point in that buffer. When there are multiple frames, each frame can display one cursor. The cursor in the selected frame is solid; the cursor in other frames is a hollow box, and appears in the window that would be selected if you give the input focus to that frame. The term `point' comes from the character `.', which was the command in TECO (the language in which the original Emacs was written) for accessing the value now called `point'. File: emacs, Node: Echo Area, Next: Mode Line, Prev: Point, Up: Screen The Echo Area ============= The line at the bottom of the frame (below the mode line) is the "echo area". It is used to display small amounts of text for several purposes. "Echoing" means displaying the characters that you type. Outside Emacs, the operating system normally echoes all your input. Emacs handles echoing differently. Single-character commands do not echo in Emacs, and multi-character commands echo only if you pause while typing them. As soon as you pause for more than a second in the middle of a command, Emacs echoes all the characters of the command so far. This is to "prompt" you for the rest of the command. Once echoing has started, the rest of the command echoes immediately as you type it. This behavior is designed to give confident users fast response, while giving hesitant users maximum feedback. You can change this behavior by setting a variable (*note Display Vars::.). If a command cannot be executed, it may print an "error message" in the echo area. Error messages are accompanied by a beep or by flashing the screen. Also, any input you have typed ahead is thrown away when an error happens. Some commands print informative messages in the echo area. These messages look much like error messages, but they are not announced with a beep and do not throw away input. Sometimes the message tells you what the command has done, when this is not obvious from looking at the text being edited. Sometimes the sole purpose of a command is to print a message giving you specific information--for example, `C-x =' prints a message describing the character position of point in the text and its current column in the window. Commands that take a long time often display messages ending in `...' while they are working, and add `done' at the end when they are finished. Echo area informative messages are saved in an editor buffer named `*Messages*'. (We have not explained buffers yet; see *Note Buffers::, for more information about them.) If you miss a message that appears briefly on the screen, you can switch to the `*Messages*' buffer to see it again. Successive progress messages are often collapsed into one. The size of `*Messages*' is limited to a certain number of lines. The variable `message-log-max' specifies how many lines. Once the buffer has that many lines, each line added at the end deletes one line from the beginning. *Note Variables::, for how to set variables such as `message-log-max'. The echo area is also used to display the "minibuffer", a window that is used for reading arguments to commands, such as the name of a file to be edited. When the minibuffer is in use, the echo area begins with a prompt string that usually ends with a colon; also, the cursor appears in that line because it is the selected window. You can always get out of the minibuffer by typing `C-g'. *Note Minibuffer::. File: emacs, Node: Mode Line, Prev: Echo Area, Up: Screen The Mode Line ============= Each text window's last line is a "mode line" which describes what is going on in that window. When there is only one text window, the mode line appears right above the echo area. The mode line is in inverse video if the terminal supports that, it starts and ends with dashes, and it contains text like `Emacs: SOMETHING'. A few special editing modes, such as Dired and Rmail, display something else in place of `Emacs: SOMETHING'. The rest of the mode line still has the usual meaning. Normally, the mode line looks like this: --CH-Emacs: BUF (MAJOR MINOR)--LINE--POS------ This gives information about the buffer being displayed in the window: the buffer's name, what major and minor modes are in use, whether the buffer's text has been changed, and how far down the buffer you are currently looking. CH contains two stars `**' if the text in the buffer has been edited (the buffer is "modified"), or `--' if the buffer has not been edited. For a read-only buffer, it is `%*' if the buffer is modified, and `%%' otherwise. BUF is the name of the window's "buffer". In most cases this is the same as the name of a file you are editing. *Note Buffers::. The buffer displayed in the selected window (the window that the cursor is in) is also Emacs's selected buffer, the one that editing takes place in. When we speak of what some command does to "the buffer", we are talking about the currently selected buffer. LINE is `L' followed by the current line number of point. This is present when Line Number mode is enabled (which it normally is). You can optionally display the current column number too, by turning on Column Number mode (which is not enabled by default because it is somewhat slower). *Note Optional Mode Line::. POS tells you whether there is additional text above the top of the window, or below the bottom. If your buffer is small and it is all visible in the window, POS is `All'. Otherwise, it is `Top' if you are looking at the beginning of the buffer, `Bot' if you are looking at the end of the buffer, or `NN%', where NN is the percentage of the buffer above the top of the window. MAJOR is the name of the "major mode" in effect in the buffer. At any time, each buffer is in one and only one of the possible major modes. The major modes available include Fundamental mode (the least specialized), Text mode, Lisp mode, C mode, Texinfo mode, and many others. *Note Major Modes::, for details of how the modes differ and how to select one. Some major modes display additional information after the major mode name. For example, Rmail buffers display the current message number and the total number of messages. Compilation buffers and Shell buffers display the status of the subprocess. MINOR is a list of some of the "minor modes" that are turned on at the moment in the window's chosen buffer. For example, `Fill' means that Auto Fill mode is on. `Abbrev' means that Word Abbrev mode is on. `Ovwrt' means that Overwrite mode is on. *Note Minor Modes::, for more information. `Narrow' means that the buffer being displayed has editing restricted to only a portion of its text. This is not really a minor mode, but is like one. *Note Narrowing::. `Def' means that a keyboard macro is being defined. *Note Keyboard Macros::. In addition, if Emacs is currently inside a recursive editing level, square brackets (`[...]') appear around the parentheses that surround the modes. If Emacs is in one recursive editing level within another, double square brackets appear, and so on. Since recursive editing levels affect Emacs globally, not just one buffer, the square brackets appear in every window's mode line or not in any of them. *Note Recursive Edit::. *Note Optional Mode Line::, for features that add other handy information to the mode line, such as the current line number of point, the current time, and whether new mail for you has arrived. File: emacs, Node: User Input, Next: Keys, Prev: Screen, Up: Top Kinds of User Input =================== GNU Emacs uses an extension of the ASCII character set for keyboard input; it also accepts non-character input events including function keys and mouse button actions. ASCII consists of 128 character codes. Some of these codes are assigned graphic symbols such as `a' and `='; the rest are control characters, such as `Control-a' (usually written `C-a' for short). `C-a' gets its name from the fact that you type it by holding down the CTRL key while pressing `a'. Some control characters have special names, and special keys you can type them with: for example, RET, TAB, LFD, DEL and ESC. The space character is usually referred to below as SPC, even though strictly speaking it is a graphic character whose graphic happens to be blank. On ASCII terminals, there are only 32 possible control characters. These are the control variants of letters and `@[]\^_'. In addition, the shift key is meaningless with control characters: `C-a' and `C-A' are the same character, and Emacs cannot distinguish them. But the Emacs character set has room for control variants of all characters, and for distinguishing between `C-a' and `C-A'. X Windows makes it possible to enter all these characters. For example, `C--' (that's Control-Minus) and `C-5' are meaningful Emacs commands under X. Another Emacs character set extension is that characters have additional modifier bits. Only one modifier bit is commonly used; it is called Meta. Every character has a Meta variant; examples include `Meta-a' (normally written `M-a', for short), `M-A' (not the same character as `M-a', but those two characters normally have the same meaning in Emacs), `M-RET', and `M-C-a'. For reasons of tradition, we usually write `C-M-a' rather than `M-C-a'; logically speaking, the order in which the modifier keys CTRL and META are mentioned does not matter. Some terminals have a META key, and allow you to type Meta characters by holding this key down. Thus, `Meta-a' is typed by holding down META and pressing `a'. The META key works much like the SHIFT key. Such a key is not always labeled META, however, as this function is often a special option for a key with some other primary purpose. If there is no META key, you can still type Meta characters using two-character sequences starting with ESC. Thus, to enter `M-a', you could type `ESC a'. To enter `C-M-a', you would type `ESC C-a'. ESC is allowed on terminals with META keys, too, in case you have formed a habit of using it. X Windows provides several other modifier keys that can be applied to any input character. These are called SUPER, HYPER and ALT. We write `s-', `H-' and `A-' to say that a character uses these modifiers. Thus, `s-H-C-x' is short for `Super-Hyper-Control-x'. Not all X terminals actually provide keys for these modifier flags--in fact, many terminals have a key labeled ALT which is really a META key. The standard key bindings of Emacs do not include any characters with these modifiers. But you can assign them meanings of your own by customizing Emacs. Keyboard input includes keyboard keys that are not characters at all: for example function keys and arrow keys. Mouse buttons are also outside the gamut of characters. You can modify these events with the modifier keys CONTROL, META, SUPER, HYPER and ALT like keyboard characters. Input characters and non-character inputs are collectively called "input events". *Note Input Events: (elisp)Input Events, for more information. If you are not doing Lisp programming, but simply want to redefine the meaning of some characters or non-character events, see *Note Customization::. ASCII terminals cannot really send anything to the computer except ASCII characters. These terminals use a sequence of characters to represent each function key. But that is invisible to the Emacs user, because the keyboard input routines recognize these special sequences and convert them to function key events before any other part of Emacs gets to see them. File: emacs, Node: Keys, Next: Commands, Prev: User Input, Up: Top Keys ==== A "key sequence" ("key", for short) is a sequence of input events that are meaningful as a unit--as "a single command." Some Emacs command sequences are just one character or one event; for example, just `C-f' is enough to move forward one character. But Emacs also has commands that take two or more events to invoke. If a sequence of events is enough to invoke a command, it is a "complete key". Examples of complete keys include `C-a', `X', RET, NEXT (a function key), DOWN (an arrow key), `C-x C-f' and `C-x 4 C-f'. If it isn't long enough to be complete, we call it a "prefix key". The above examples show that `C-x' and `C-x 4' are prefix keys. Every key sequence is either a complete key or a prefix key. Most single characters constitute complete keys in the standard Emacs command bindings. A few of them are prefix keys. A prefix key combines with the following input event to make a longer key sequence, which may itself be complete or a prefix. For example, `C-x' is a prefix key, so `C-x' and the next input event combine to make a two-character key sequence. Most of these key sequences are complete keys, including `C-x C-f' and `C-x b'. A few, such as `C-x 4' and `C-x r', are themselves prefix keys that lead to three-character key sequences. There's no limit to the length of a key sequence, but in practice people rarely use sequences longer than four events. By contrast, you can't add more events onto a complete key. For example, the two-character sequence `C-f C-k' is not a key, because the `C-f' is a complete key in itself. It's impossible to give `C-f C-k' an independent meaning as a command. `C-f C-k' is two key sequences, not one. All told, the prefix keys in Emacs are `C-c', `C-h', `C-x', `C-x C-a', `C-x n', `C-x r', `C-x v', `C-x 4', `C-x 5', `C-x 6', and ESC. But this is not cast in concrete; it is just a matter of Emacs's standard key bindings. If you customize Emacs, you can make new prefix keys, or eliminate these. *Note Key Bindings::. If you do make or eliminate prefix keys, that changes the set of possible key sequences. For example, if you redefine `C-f' as a prefix, `C-f C-k' automatically becomes a key (complete, unless you define it too as a prefix). Conversely, if you remove the prefix definition of `C-x 4', then `C-x 4 f' (or `C-x 4 ANYTHING') is no longer a key. Typing the help character (`C-h' or F1) after a prefix character displays a list of the commands starting with that prefix. There are a few prefix characters for which `C-h' does not work--for historical reasons, they have other meanings for `C-h' which are not easy to change. But F1 should work for all prefix characters. File: emacs, Node: Commands, Next: Text Characters, Prev: Keys, Up: Top Keys and Commands ================= This manual is full of passages that tell you what particular keys do. But Emacs does not assign meanings to keys directly. Instead, Emacs assigns meanings to named "commands", and then gives keys their meanings by "binding" them to commands. Every command has a name chosen by a programmer. The name is usually made of a few English words separated by dashes; for example, `next-line' or `forward-word'. A command also has a "function definition" which is a Lisp program; this is what makes the command do what it does. In Emacs Lisp, a command is actually a special kind of Lisp function; one which specifies how to read arguments for it and call it interactively. For more information on commands and functions, see *Note What Is a Function: (elisp)What Is a Function. (The definition we use in this manual is simplified slightly.) The bindings between keys and commands are recorded in various tables called "keymaps". *Note Keymaps::. When we say that "`C-n' moves down vertically one line" we are glossing over a distinction that is irrelevant in ordinary use but is vital in understanding how to customize Emacs. It is the command `next-line' that is programmed to move down vertically. `C-n' has this effect *because* it is bound to that command. If you rebind `C-n' to the command `forward-word' then `C-n' will move forward by words instead. Rebinding keys is a common method of customization. In the rest of this manual, we usually ignore this subtlety to keep things simple. To give the information needed for customization, we state the name of the command which really does the work in parentheses after mentioning the key that runs it. For example, we will say that "The command `C-n' (`next-line') moves point vertically down," meaning that `next-line' is a command that moves vertically down and `C-n' is a key that is standardly bound to it. While we are on the subject of information for customization only, it's a good time to tell you about "variables". Often the description of a command will say, "To change this, set the variable `mumble-foo'." A variable is a name used to remember a value. Most of the variables documented in this manual exist just to facilitate customization: some command or other part of Emacs examines the variable and behaves differently according to the value that you set. Until you are interested in customizing, you can ignore the information about variables. When you are ready to be interested, read the basic information on variables, and then the information on individual variables will make sense. *Note Variables::. File: emacs, Node: Text Characters, Next: Entering Emacs, Prev: Commands, Up: Top Character Set for Text ====================== Emacs buffers use an 8-bit character set, because bytes have 8 bits. ASCII graphic characters in Emacs buffers are displayed with their graphics. The newline character (which has the same character code as LFD) is displayed by starting a new line. The tab character is displayed by moving to the next tab stop column (normally every 8 columns). Other control characters are displayed as a caret (`^') followed by the non-control version of the character; thus, `C-a' is displayed as `^A'. Non-ASCII characters 128 and up are displayed with octal escape sequences; thus, character code 243 (octal) is displayed as `\243'. You can customize the display of these character codes (or ASCII characters) by creating a "display table". *Note Display Tables: (elisp)Display Tables. This is useful for editing files that use 8-bit European character sets. *Note European Display::. File: emacs, Node: Entering Emacs, Next: Exiting, Prev: Text Characters, Up: Top Entering and Exiting Emacs ************************** The usual way to invoke Emacs is with the shell command `emacs'. Emacs clears the screen and then displays an initial help message and copyright notice. Some operating systems discard all type-ahead when Emacs starts up; they give Emacs no way to prevent this. Therefore, it is advisable to wait until Emacs clears the screen before typing your first editing command. If you run Emacs from a shell window under the X Window System, run it in the background with `emacs&'. This way, Emacs does not tie up the shell window, so you can use that to run other shell commands while Emacs operates its own X windows. You can begin typing Emacs commands as soon as you direct your keyboard input to the Emacs frame. When Emacs starts up, it makes a buffer named `*scratch*'. That's the buffer you start out in. The `*scratch*' buffer uses Lisp Interaction mode; you can use it to type Lisp expressions and evaluate them, or you can ignore that capability and simply doodle. (You can specify a different major mode for this buffer by setting the variable `initial-major-mode' in your init file. *Note Init File::.) It is possible to specify files to be visited, Lisp files to be loaded, and functions to be called, by giving Emacs arguments in the shell command line. *Note Command Arguments::. But we don't recommend doing this. The feature exists mainly for compatibility with other editors. Many other editors are designed to be started afresh each time you want to edit. You edit one file and then exit the editor. The next time you want to edit either another file or the same one, you must run the editor again. With these editors, it makes sense to use a command line argument to say which file to edit. But starting a new Emacs each time you want to edit a different file does not make sense. For one thing, this would be annoyingly slow. For another, this would fail to take advantage of Emacs's ability to visit more than one file in a single editing session. And it would lose the other accumulated context, such as registers, undo history, and the mark ring. The recommended way to use GNU Emacs is to start it only once, just after you log in, and do all your editing in the same Emacs session. Each time you want to edit a different file, you visit it with the existing Emacs, which eventually comes to have many files in it ready for editing. Usually you do not kill the Emacs until you are about to log out. *Note Files::, for more information on visiting more than one file.