1 @c This is part of the Emacs manual.
2 @c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2000, 2001,
3 @c 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
4 @c See file emacs.texi for copying conditions.
5 @node Building, Maintaining, Programs, Top
6 @chapter Compiling and Testing Programs
7 @cindex building programs
8 @cindex program building
9 @cindex running Lisp functions
11 The previous chapter discusses the Emacs commands that are useful for
12 making changes in programs. This chapter deals with commands that assist
13 in the larger process of compiling and testing programs.
16 * Compilation:: Compiling programs in languages other
17 than Lisp (C, Pascal, etc.).
18 * Compilation Mode:: The mode for visiting compiler errors.
19 * Compilation Shell:: Customizing your shell properly
20 for use in the compilation buffer.
21 * Grep Searching:: Searching with grep.
22 * Flymake:: Finding syntax errors on the fly.
23 * Debuggers:: Running symbolic debuggers for non-Lisp programs.
24 * Executing Lisp:: Various modes for editing Lisp programs,
25 with different facilities for running
27 * Libraries: Lisp Libraries. Creating Lisp programs to run in Emacs.
28 * Eval: Lisp Eval. Executing a single Lisp expression in Emacs.
29 * Interaction: Lisp Interaction. Executing Lisp in an Emacs buffer.
30 * External Lisp:: Communicating through Emacs with a separate Lisp.
34 @section Running Compilations under Emacs
35 @cindex inferior process
37 @cindex compilation errors
40 Emacs can run compilers for noninteractive languages such as C and
41 Fortran as inferior processes, feeding the error log into an Emacs buffer.
42 It can also parse the error messages and show you the source lines where
43 compilation errors occurred.
47 Run a compiler asynchronously under Emacs, with error messages going to
48 the @samp{*compilation*} buffer.
50 Invoke a compiler with the same command as in the last invocation of
52 @item M-x kill-compilation
53 Kill the running compilation subprocess.
57 To run @code{make} or another compilation command, do @kbd{M-x
58 compile}. This command reads a shell command line using the minibuffer,
59 and then executes the command in an inferior shell, putting output in
60 the buffer named @samp{*compilation*}. The current buffer's default
61 directory is used as the working directory for the execution of the
62 command; normally, therefore, the compilation happens in this
65 @vindex compile-command
66 The default for the compilation command is normally @samp{make -k},
67 which is correct most of the time for nontrivial programs.
68 (@xref{Top,, Make, make, GNU Make Manual}.) If you have done @kbd{M-x
69 compile} before, the default each time is the command you used the
70 previous time. @code{compile} stores this command in the variable
71 @code{compile-command}, so setting that variable specifies the default
72 for the next use of @kbd{M-x compile}. If a file specifies a file
73 local value for @code{compile-command}, that provides the default when
74 you type @kbd{M-x compile} in that file's buffer. @xref{File
77 Starting a compilation displays the buffer @samp{*compilation*} in
78 another window but does not select it. The buffer's mode line tells
79 you whether compilation is finished, with the word @samp{run},
80 @samp{signal} or @samp{exit} inside the parentheses. You do not have
81 to keep this buffer visible; compilation continues in any case. While
82 a compilation is going on, the string @samp{Compiling} appears in the
83 mode lines of all windows. When this string disappears, the
84 compilation is finished.
86 If you want to watch the compilation transcript as it appears, switch
87 to the @samp{*compilation*} buffer and move point to the end of the
88 buffer. When point is at the end, new compilation output is inserted
89 above point, which remains at the end. If point is not at the end of
90 the buffer, it remains fixed while more compilation output is added at
91 the end of the buffer.
93 @cindex compilation buffer, keeping point at end
94 @vindex compilation-scroll-output
95 If you set the variable @code{compilation-scroll-output} to a
96 non-@code{nil} value, then the compilation buffer always scrolls to
97 follow output as it comes in.
100 To rerun the last compilation with the same command, type @kbd{M-x
101 recompile}. This automatically reuses the compilation command from
102 the last invocation of @kbd{M-x compile}. It also reuses the
103 @samp{*compilation*} buffer and starts the compilation in its default
104 directory, which is the directory in which the previous compilation
107 When the compiler process terminates, for whatever reason, the mode
108 line of the @samp{*compilation*} buffer changes to say @samp{exit}
109 (followed by the exit code, @samp{[0]} for a normal exit), or
110 @samp{signal} (if a signal terminated the process), instead of
113 @findex kill-compilation
114 Starting a new compilation also kills any compilation already
115 running in @samp{*compilation*}, as the buffer can only handle one
116 compilation at any time. However, @kbd{M-x compile} asks for
117 confirmation before actually killing a compilation that is running.
118 You can also kill the compilation process with @kbd{M-x
121 If you want to run two compilations at once, you should start the
122 first one, then rename the @samp{*compilation*} buffer (perhaps using
123 @code{rename-uniquely}; @pxref{Misc Buffer}), and start the other
124 compilation. That will create a new @samp{*compilation*} buffer.
126 Emacs does not expect a compiler process to launch asynchronous
127 subprocesses; if it does, and they keep running after the main
128 compiler process has terminated, Emacs may kill them or their output
129 may not arrive in Emacs. To avoid this problem, make the main process
130 wait for its subprocesses to finish. In a shell script, you can do this
131 using @samp{$!} and @samp{wait}, like this:
134 (sleep 10; echo 2nd)& pid=$! # @r{Record pid of subprocess}
136 wait $pid # @r{Wait for subprocess}
139 If the background process does not output to the compilation buffer,
140 so you only need to prevent it from being killed when the main
141 compilation process terminates, this is sufficient:
144 nohup @var{command}; sleep 1
147 @vindex compilation-environment
148 You can control the environment passed to the compilation command
149 with the variable @code{compilation-environment}. Its value is a list
150 of environment variable settings; each element should be a string of
151 the form @code{"@var{envvarname}=@var{value}"}. These environment
152 variable settings override the usual ones.
154 @node Compilation Mode
155 @section Compilation Mode
157 @cindex Compilation mode
158 @cindex mode, Compilation
159 The @samp{*compilation*} buffer uses a special major mode,
160 Compilation mode, whose main feature is to provide a convenient way to
161 visit the source line corresponding to an error message. These
162 commands are also available in other special buffers that list
163 locations in files, including those made by @kbd{M-x grep} and
170 Visit the locus of the next error message or match.
173 Visit the locus of the previous error message or match.
175 Visit the locus of the error message that point is on.
176 This command is used in the compilation buffer.
178 Visit the locus of the error message that you click on.
180 Find and highlight the locus of the next error message, without
181 selecting the source buffer.
183 Find and highlight the locus of the previous error message, without
184 selecting the source buffer.
186 Move point to the next error for a different file than the current
189 Move point to the previous error for a different file than the current
192 Toggle Next Error Follow minor mode, which makes cursor motion in the
193 compilation buffer produce automatic source display.
196 @findex compile-goto-error
197 You can visit the source for any particular error message by moving
198 point in the @samp{*compilation*} buffer to that error message and
199 typing @key{RET} (@code{compile-goto-error}). Alternatively, you can
200 click @kbd{Mouse-2} on the error message; you need not switch to the
201 @samp{*compilation*} buffer first.
207 @vindex next-error-highlight
208 To parse the compiler error messages sequentially, type @kbd{C-x `}
209 (@code{next-error}). The character following the @kbd{C-x} is the
210 backquote or ``grave accent,'' not the single-quote. This command is
211 available in all buffers, not just in @samp{*compilation*}; it
212 displays the next error message at the top of one window and source
213 location of the error in another window. It also momentarily
214 highlights the relevant source line. You can change the behavior of
215 this highlighting with the variable @code{next-error-highlight}.
217 The first time @w{@kbd{C-x `}} is used after the start of a compilation,
218 it moves to the first error's location. Subsequent uses of @kbd{C-x
219 `} advance down to subsequent errors. If you visit a specific error
220 message with @key{RET} or @kbd{Mouse-2}, subsequent @w{@kbd{C-x `}}
221 commands advance from there. When @w{@kbd{C-x `}} gets to the end of the
222 buffer and finds no more error messages to visit, it fails and signals
223 an Emacs error. @w{@kbd{C-u C-x `}} starts scanning from the beginning of
224 the compilation buffer, and goes to the first error's location.
226 @vindex compilation-skip-threshold
227 By default, @w{@kbd{C-x `}} skips less important messages. The variable
228 @code{compilation-skip-threshold} controls this. If its value is 2,
229 @w{@kbd{C-x `}} skips anything less than error, 1 skips anything less
230 than warning, and 0 doesn't skip any messages. The default is 1.
232 When the window has a left fringe, an arrow in the fringe points to
233 the current message in the compilation buffer. The variable
234 @code{compilation-context-lines} controls the number of lines of
235 leading context to display before the current message. Going to an
236 error message location scrolls the @samp{*compilation*} buffer to put
237 the message that far down from the top. The value @code{nil} is
238 special: if there's a left fringe, the window doesn't scroll at all
239 if the message is already visible. If there is no left fringe,
240 @code{nil} means display the message at the top of the window.
242 If you're not in the compilation buffer when you run
243 @code{next-error}, Emacs will look for a buffer that contains error
244 messages. First, it looks for one displayed in the selected frame,
245 then for one that previously had @code{next-error} called on it, and
246 then at the current buffer. Finally, Emacs looks at all the remaining
247 buffers. @code{next-error} signals an error if it can't find any such
250 @vindex compilation-error-regexp-alist
251 @vindex grep-regexp-alist
252 To parse messages from the compiler, Compilation mode uses the
253 variable @code{compilation-error-regexp-alist} which lists various
254 formats of error messages and tells Emacs how to extract the source file
255 and the line number from the text of a message. If your compiler isn't
256 supported, you can tailor Compilation mode to it by adding elements to
257 that list. A similar variable @code{grep-regexp-alist} tells Emacs how
258 to parse output of a @code{grep} command.
260 @findex compilation-next-error
261 @findex compilation-previous-error
262 @findex compilation-next-file
263 @findex compilation-previous-file
264 Compilation mode also redefines the keys @key{SPC} and @key{DEL} to
265 scroll by screenfuls, and @kbd{M-n} (@code{compilation-next-error})
266 and @kbd{M-p} (@code{compilation-previous-error}) to move to the next
267 or previous error message. You can also use @kbd{M-@{}
268 (@code{compilation-next-file} and @kbd{M-@}}
269 (@code{compilation-previous-file}) to move up or down to an error
270 message for a different source file.
272 @cindex Next Error Follow mode
273 @findex next-error-follow-minor-mode
274 You can type @kbd{C-c C-f} to toggle Next Error Follow mode. In
275 this minor mode, ordinary cursor motion in the compilation buffer
276 automatically updates the source buffer. For instance, moving the
277 cursor to the next error message causes the location of that error to
278 be displayed immediately.
280 The features of Compilation mode are also available in a minor mode
281 called Compilation Minor mode. This lets you parse error messages in
282 any buffer, not just a normal compilation output buffer. Type @kbd{M-x
283 compilation-minor-mode} to enable the minor mode. This defines the keys
284 @key{RET} and @kbd{Mouse-2}, as in the Compilation major mode.
286 Compilation minor mode works in any buffer, as long as the contents
287 are in a format that it understands. In an Rlogin buffer (@pxref{Remote
288 Host}), Compilation minor mode automatically accesses remote source
289 files by FTP (@pxref{File Names}).
291 @node Compilation Shell
292 @section Subshells for Compilation
294 Emacs uses a shell to run the compilation command, but specifies the
295 option for a noninteractive shell. This means, in particular, that
296 the shell should start with no prompt. If you find your usual shell
297 prompt making an unsightly appearance in the @samp{*compilation*}
298 buffer, it means you have made a mistake in your shell's init file by
299 setting the prompt unconditionally. (This init file's name may be
300 @file{.bashrc}, @file{.profile}, @file{.cshrc}, @file{.shrc}, or
301 various other things, depending on the shell you use.) The shell init
302 file should set the prompt only if there already is a prompt. Here's
303 how to do it in bash:
306 if [ "$@{PS1+set@}" = set ]
312 And here's how to do it in csh:
315 if ($?prompt) set prompt = @dots{}
318 There may well be other things that your shell's init file
319 ought to do only for an interactive shell. You can use the same
320 method to conditionalize them.
322 The MS-DOS ``operating system'' does not support asynchronous
323 subprocesses; to work around this lack, @kbd{M-x compile} runs the
324 compilation command synchronously on MS-DOS. As a consequence, you must
325 wait until the command finishes before you can do anything else in
328 @inforef{MS-DOS,,emacs-xtra}.
335 @section Searching with Grep under Emacs
337 Just as you can run a compiler from Emacs and then visit the lines
338 with compilation errors, you can also run @code{grep} and
339 then visit the lines on which matches were found. This works by
340 treating the matches reported by @code{grep} as if they were ``errors.''
345 Run @code{grep} asynchronously under Emacs, with matching lines
346 listed in the buffer named @samp{*grep*}.
350 Run @code{grep} via @code{find}, with user-specified arguments, and
351 collect output in the buffer named @samp{*grep*}.
353 Kill the running @code{grep} subprocess.
357 To run @code{grep}, type @kbd{M-x grep}, then enter a command line
358 that specifies how to run @code{grep}. Use the same arguments you
359 would give @code{grep} when running it normally: a @code{grep}-style
360 regexp (usually in single-quotes to quote the shell's special
361 characters) followed by file names, which may use wildcards. If you
362 specify a prefix argument for @kbd{M-x grep}, it finds the tag
363 (@pxref{Tags}) in the buffer around point, and puts that into the
364 default @code{grep} command.
366 Your command need not simply run @code{grep}; you can use any shell
367 command that produces output in the same format. For instance, you
368 can chain @code{grep} commands, like this:
371 grep -nH -e foo *.el | grep bar | grep toto
374 The output from @code{grep} goes in the @samp{*grep*} buffer. You
375 can find the corresponding lines in the original files using @w{@kbd{C-x
376 `}}, @key{RET}, and so forth, just like compilation errors.
378 Some grep programs accept a @samp{--color} option to output special
379 markers around matches for the purpose of highlighting. You can make
380 use of this feature by setting @code{grep-highlight-matches} to
381 @code{t}. When displaying a match in the source buffer, the exact
382 match will be highlighted, instead of the entire source line.
386 The command @kbd{M-x grep-find} (also available as @kbd{M-x
387 find-grep}) is similar to @kbd{M-x grep}, but it supplies a different
388 initial default for the command---one that runs both @code{find} and
389 @code{grep}, so as to search every file in a directory tree. See also
390 the @code{find-grep-dired} command, in @ref{Dired and Find}.
394 The commands @kbd{M-x lgrep} (local grep) and @kbd{M-x rgrep}
395 (recursive grep) are more user-friendly versions of @code{grep} and
396 @code{grep-find}, which prompt separately for the regular expression
397 to match, the files to search, and the base directory for the search
398 (rgrep only). Case sensitivity of the search is controlled by the
399 current value of @code{case-fold-search}.
401 These commands build the shell commands based on the variables
402 @code{grep-template} (for @code{lgrep}) and @code{grep-find-template}
405 The files to search can use aliases defined in the variable
406 @code{grep-files-aliases}.
408 Subdirectories listed in the variable
409 @code{grep-find-ignored-directories} such as those typically used by
410 various version control systems, like CVS and arch, are automatically
411 skipped by @code{rgrep}.
414 @section Finding Syntax Errors On The Fly
415 @cindex checking syntax
417 Flymake mode is a minor mode that performs on-the-fly syntax
418 checking for many programming and markup languages, including C, C++,
419 Perl, HTML, and @TeX{}/La@TeX{}. It is somewhat analogous to Flyspell
420 mode, which performs spell checking for ordinary human languages in a
421 similar fashion (@pxref{Spelling}). As you edit a file, Flymake mode
422 runs an appropriate syntax checking tool in the background, using a
423 temporary copy of the buffer. It then parses the error and warning
424 messages, and highlights the erroneous lines in the buffer. The
425 syntax checking tool used depends on the language; for example, for
426 C/C++ files this is usually the C compiler. Flymake can also use
427 build tools such as @code{make} for checking complicated projects.
429 To activate Flymake mode, type @kbd{M-x flymake-mode}. You can move
430 to the errors spotted by Flymake mode with @kbd{M-x
431 flymake-goto-next-error} and @kbd{M-x flymake-goto-prev-error}. To
432 display any error messages associated with the current line, use
433 @kbd{M-x flymake-display-err-menu-for-current-line}.
435 For more details about using Flymake, see @ref{Top, Flymake,
436 Flymake, flymake, The Flymake Manual}.
439 @section Running Debuggers Under Emacs
451 @c Do you believe in GUD?
452 The GUD (Grand Unified Debugger) library provides an interface to
453 various symbolic debuggers from within Emacs. We recommend the
454 debugger GDB, which is free software, but GUD can also run DBX, SDB or
455 XDB. GUD can also serve as an interface to Perl's debugging mode, the
456 Python debugger PDB, the Bash debugger, and to JDB, the Java Debugger.
457 @xref{Debugging,, The Lisp Debugger, elisp, the Emacs Lisp Reference
458 Manual}, for information on debugging Emacs Lisp programs.
461 * Starting GUD:: How to start a debugger subprocess.
462 * Debugger Operation:: Connection between the debugger and source buffers.
463 * Commands of GUD:: Key bindings for common commands.
464 * GUD Customization:: Defining your own commands for GUD.
465 * GDB Graphical Interface:: An enhanced mode that uses GDB features to
466 implement a graphical debugging environment through
471 @subsection Starting GUD
473 There are several commands for starting a debugger, each corresponding
474 to a particular debugger program.
477 @item M-x gdb @key{RET} @var{file} @key{RET}
479 Run GDB as a subprocess of Emacs. By default, this uses an IDE-like
480 graphical interface; see @ref{GDB Graphical Interface}. Only GDB
481 works with the graphical interface.
483 @item M-x dbx @key{RET} @var{file} @key{RET}
485 Run DBX as a subprocess of Emacs. Since Emacs does not implement a
486 graphical interface for DBX, communication with DBX works by typing
487 commands in the GUD interaction buffer. The same is true for all
488 the other supported debuggers.
490 @item M-x xdb @key{RET} @var{file} @key{RET}
492 @vindex gud-xdb-directories
493 Similar, but run XDB. Use the variable
494 @code{gud-xdb-directories} to specify directories to search for source
497 @item M-x sdb @key{RET} @var{file} @key{RET}
499 Similar, but run SDB.
501 Some versions of SDB do not mention source file names in their
502 messages. When you use them, you need to have a valid tags table
503 (@pxref{Tags}) in order for GUD to find functions in the source code.
504 If you have not visited a tags table or the tags table doesn't list one
505 of the functions, you get a message saying @samp{The sdb support
506 requires a valid tags table to work}. If this happens, generate a valid
507 tags table in the working directory and try again.
509 @item M-x bashdb @key{RET} @var{file} @key{RET}
511 Run the bash debugger to debug @var{file}, a shell script.
513 @item M-x perldb @key{RET} @var{file} @key{RET}
515 Run the Perl interpreter in debug mode to debug @var{file}, a Perl program.
517 @item M-x jdb @key{RET} @var{file} @key{RET}
519 Run the Java debugger to debug @var{file}.
521 @item M-x pdb @key{RET} @var{file} @key{RET}
523 Run the Python debugger to debug @var{file}.
526 Each of these commands takes one argument: a command line to invoke
527 the debugger. In the simplest case, specify just the name of the
528 executable file you want to debug. You may also use options that the
529 debugger supports. However, shell wildcards and variables are not
530 allowed. GUD assumes that the first argument not starting with a
531 @samp{-} is the executable file name.
533 @node Debugger Operation
534 @subsection Debugger Operation
536 @cindex fringes, and current execution line in GUD
537 When you run a debugger with GUD using the textual interface, the
538 debugger uses an Emacs buffer for its ordinary input and output. This
539 is called the GUD buffer. Input and output from the program you are
540 debugging also use this buffer.
542 The debugger displays the source files of the program by visiting
543 them in Emacs buffers. An arrow in the left fringe indicates the
544 current execution line.@footnote{On a text-only terminal, the arrow
545 appears as @samp{=>} and overlays the first two text columns.} Moving
546 point in this buffer does not move the arrow. The arrow is not part
547 of the file's text; it appears only on the screen.
549 You can start editing these source files at any time in the buffers
550 that display them. If you do modify a source file, keep in mind that
551 inserting or deleting lines will throw off the arrow's positioning;
552 GUD has no way of figuring out which line corresponded before your
553 changes to the line number in a debugger message. Also, you'll
554 typically have to recompile and restart the program for your changes
555 to be reflected in the debugger's tables.
557 @cindex tooltips with GUD
558 @vindex tooltip-gud-modes
559 @vindex gud-tooltip-mode
560 @vindex gud-tooltip-echo-area
561 The Tooltip facility (@pxref{Tooltips}) provides support for GUD@.
562 You activate this feature by turning on the minor mode
563 @code{gud-tooltip-mode}. Then you can display a variable's value in a
564 tooltip simply by pointing at it with the mouse. In graphical mode,
565 with a C program, you can also display the @code{#define} directive
566 associated with an identifier when the program is not executing. This
567 operates in the GUD buffer and in source buffers with major modes in
568 the list @code{gud-tooltip-modes}. If the variable
569 @code{gud-tooltip-echo-area} is non-@code{nil} then the variable's
570 value is displayed in the echo area.
572 GUD tooltips are disabled when you use GDB in text command mode
573 (@pxref{GDB Graphical Interface}), because displaying an expression's
574 value in GDB can sometimes expand a macro and result in a side effect
575 that interferes with the program's operation. The GDB graphical
576 interface supports GUD tooltips and assures they will not cause side
579 @node Commands of GUD
580 @subsection Commands of GUD
582 The GUD interaction buffer uses a variant of Shell mode, so the
583 Emacs commands of Shell mode are available (@pxref{Shell Mode}). All
584 the usual commands for your debugger are available, and you can use
585 the Shell mode history commands to repeat them. If you wish, you can
586 control your debugger process entirely through this buffer.
588 GUD mode also provides commands for setting and clearing
589 breakpoints, for selecting stack frames, and for stepping through the
590 program. These commands are available both in the GUD buffer and
591 globally, but with different key bindings. It also has its own tool
592 bar from which you can invoke the more common commands by clicking on
593 the appropriate icon. This is particularly useful for repetitive
594 commands like @code{gud-next} and @code{gud-step}, and allows you to
595 keep the GUD buffer hidden.
597 The breakpoint commands are normally used in source file buffers,
598 because that is the easiest way to specify where to set or clear the
599 breakpoint. Here's the global command to set a breakpoint:
604 Set a breakpoint on the source line that point is on.
607 @kindex C-x C-a @r{(GUD)}
608 Here are the other special commands provided by GUD@. The keys
609 starting with @kbd{C-c} are available only in the GUD interaction
610 buffer. The key bindings that start with @kbd{C-x C-a} are available
611 in the GUD interaction buffer and also in source files. Some of these
612 commands are not available to all the supported debuggers.
616 @kindex C-c C-l @r{(GUD)}
619 Display in another window the last line referred to in the GUD
620 buffer (that is, the line indicated in the last location message).
621 This runs the command @code{gud-refresh}.
624 @kindex C-c C-s @r{(GUD)}
627 Execute a single line of code (@code{gud-step}). If the line contains
628 a function call, execution stops after entering the called function.
631 @kindex C-c C-n @r{(GUD)}
634 Execute a single line of code, stepping across entire function calls
635 at full speed (@code{gud-next}).
638 @kindex C-c C-i @r{(GUD)}
641 Execute a single machine instruction (@code{gud-stepi}).
644 @kindex C-c C-p @r{(GUD)}
647 Evaluate the expression at point (@code{gud-print}). If Emacs
648 does not print the exact expression that you want, mark it as a region
653 @kindex C-c C-r @r{(GUD)}
656 Continue execution without specifying any stopping point. The program
657 will run until it hits a breakpoint, terminates, or gets a signal that
658 the debugger is checking for (@code{gud-cont}).
662 @kindex C-c C-d @r{(GUD)}
665 Delete the breakpoint(s) on the current source line, if any
666 (@code{gud-remove}). If you use this command in the GUD interaction
667 buffer, it applies to the line where the program last stopped.
670 @kindex C-c C-t @r{(GUD)}
673 Set a temporary breakpoint on the current source line, if any
674 (@code{gud-tbreak}). If you use this command in the GUD interaction
675 buffer, it applies to the line where the program last stopped.
678 @kindex C-c < @r{(GUD)}
681 Select the next enclosing stack frame (@code{gud-up}). This is
682 equivalent to the GDB command @samp{up}.
685 @kindex C-c > @r{(GUD)}
688 Select the next inner stack frame (@code{gud-down}). This is
689 equivalent to the GDB command @samp{down}.
692 @kindex C-c C-u @r{(GUD)}
695 Continue execution to the current line (@code{gud-until}). The
696 program will run until it hits a breakpoint, terminates, gets a signal
697 that the debugger is checking for, or reaches the line on which the
698 cursor currently sits.
701 @kindex C-c C-f @r{(GUD)}
704 Run the program until the selected stack frame returns or
705 stops for some other reason (@code{gud-finish}).
708 If you are using GDB, these additional key bindings are available:
712 @kindex C-x C-a C-j @r{(GUD)}
714 Only useful in a source buffer, @code{gud-jump} transfers the
715 program's execution point to the current line. In other words, the
716 next line that the program executes will be the one where you gave the
717 command. If the new execution line is in a different function from
718 the previously one, GDB prompts for confirmation since the results may
719 be bizarre. See the GDB manual entry regarding @code{jump} for
723 @kindex TAB @r{(GUD)}
724 @findex gud-gdb-complete-command
725 With GDB, complete a symbol name (@code{gud-gdb-complete-command}).
726 This key is available only in the GUD interaction buffer.
729 These commands interpret a numeric argument as a repeat count, when
732 Because @key{TAB} serves as a completion command, you can't use it to
733 enter a tab as input to the program you are debugging with GDB.
734 Instead, type @kbd{C-q @key{TAB}} to enter a tab.
736 @node GUD Customization
737 @subsection GUD Customization
739 @vindex gdb-mode-hook
740 @vindex dbx-mode-hook
741 @vindex sdb-mode-hook
742 @vindex xdb-mode-hook
743 @vindex perldb-mode-hook
744 @vindex pdb-mode-hook
745 @vindex jdb-mode-hook
746 @vindex bashdb-mode-hook
747 On startup, GUD runs one of the following hooks: @code{gdb-mode-hook},
748 if you are using GDB; @code{dbx-mode-hook}, if you are using DBX;
749 @code{sdb-mode-hook}, if you are using SDB; @code{xdb-mode-hook}, if you
750 are using XDB; @code{perldb-mode-hook}, for Perl debugging mode;
751 @code{pdb-mode-hook}, for PDB; @code{jdb-mode-hook}, for JDB;
752 @code{bashdb-mode-hook}, for the Bash debugger. You can
753 use these hooks to define custom key bindings for the debugger
754 interaction buffer. @xref{Hooks}.
756 Here is a convenient way to define a command that sends a particular
757 command string to the debugger, and set up a key binding for it in the
758 debugger interaction buffer:
762 (gud-def @var{function} @var{cmdstring} @var{binding} @var{docstring})
765 This defines a command named @var{function} which sends
766 @var{cmdstring} to the debugger process, and gives it the documentation
767 string @var{docstring}. You can then use the command @var{function} in any
768 buffer. If @var{binding} is non-@code{nil}, @code{gud-def} also binds
769 the command to @kbd{C-c @var{binding}} in the GUD buffer's mode and to
770 @kbd{C-x C-a @var{binding}} generally.
772 The command string @var{cmdstring} may contain certain
773 @samp{%}-sequences that stand for data to be filled in at the time
774 @var{function} is called:
778 The name of the current source file. If the current buffer is the GUD
779 buffer, then the ``current source file'' is the file that the program
783 The number of the current source line. If the current buffer is the GUD
784 buffer, then the ``current source line'' is the line that the program
788 In transient-mark-mode the text in the region, if it is active.
789 Otherwise the text of the C lvalue or function-call expression at or
793 The text of the hexadecimal address at or adjacent to point.
796 The numeric argument of the called function, as a decimal number. If
797 the command is used without a numeric argument, @samp{%p} stands for the
800 If you don't use @samp{%p} in the command string, the command you define
801 ignores any numeric argument.
804 The name of the directory of the current source file.
807 Fully qualified class name derived from the expression surrounding point
811 @node GDB Graphical Interface
812 @subsection GDB Graphical Interface
814 By default, the command @code{gdb} starts GDB using a graphical
815 interface, using Emacs windows for display program state information.
816 In effect, this makes Emacs into an IDE (interactive development
817 environment). With it, you do not need to use textual GDB commands;
818 you can control the debugging session with the mouse. For example,
819 you can click in the fringe of a source buffer to set a breakpoint
820 there, or on a stack frame in the stack buffer to select that frame.
822 This mode requires telling GDB that its ``screen size'' is
823 unlimited, so it sets the height and width accordingly. For correct
824 operation you must not change these values during the GDB session.
826 @vindex gud-gdb-command-name
828 You can also run GDB in text command mode, like other debuggers. To
829 do this, set @code{gud-gdb-command-name} to @code{"gdb --fullname"} or
830 edit the startup command in the minibuffer to say that. You need to
831 do use text command mode to run multiple debugging sessions within one
832 Emacs session. If you have customized @code{gud-gdb-command-name} in
833 that way, you can use @kbd{M-x gdba} to invoke GDB in graphical mode.
836 * GDB-UI Layout:: Control the number of displayed buffers.
837 * Source Buffers:: Use the mouse in the fringe/margin to
838 control your program.
839 * Breakpoints Buffer:: A breakpoint control panel.
840 * Stack Buffer:: Select a frame from the call stack.
841 * Other GDB-UI Buffers:: Input/output, locals, registers,
842 assembler, threads and memory buffers.
843 * Watch Expressions:: Monitor variable values in the speedbar.
847 @subsubsection GDB User Interface Layout
848 @cindex GDB User Interface layout
850 @vindex gdb-many-windows
851 If the variable @code{gdb-many-windows} is @code{nil} (the default
852 value) then @kbd{M-x gdb} normally displays only the GUD buffer.
853 However, if the variable @code{gdb-show-main} is also non-@code{nil},
854 it starts with two windows: one displaying the GUD buffer, and the
855 other showing the source for the @code{main} function of the program
858 If @code{gdb-many-windows} is non-@code{nil}, then @kbd{M-x gdb}
859 displays the following frame layout:
863 +--------------------------------+--------------------------------+
864 | GUD buffer (I/O of GDB) | Locals buffer |
865 |--------------------------------+--------------------------------+
866 | Primary Source buffer | I/O buffer for debugged pgm |
867 |--------------------------------+--------------------------------+
868 | Stack buffer | Breakpoints buffer |
869 +--------------------------------+--------------------------------+
873 However, if @code{gdb-use-separate-io-buffer} is @code{nil}, the I/O
874 buffer does not appear and the primary source buffer occupies the full
877 @findex gdb-restore-windows
878 If you change the window layout, for example, while editing and
879 re-compiling your program, then you can restore this standard window
880 layout with the command @code{gdb-restore-windows}.
882 @findex gdb-many-windows
883 To switch between this standard layout and a simple layout
884 containing just the GUD buffer and a source file, type @kbd{M-x
887 You may also specify additional GDB-related buffers to display,
888 either in the same frame or a different one. Select the buffers you
889 want with the @samp{GUD->GDB-windows} and @samp{GUD->GDB-Frames}
890 sub-menus. If the menu-bar is unavailable, type @code{M-x
891 gdb-display-@var{buffertype}-buffer} or @code{M-x
892 gdb-frame-@var{buffertype}-buffer} respectively, where
893 @var{buffertype} is the relevant buffer type, such as
894 @samp{breakpoints}. Most of these buffers are read-only, and typing
895 @kbd{q} in them kills them.
897 When you finish debugging, kill the GUD buffer with @kbd{C-x k},
898 which will also kill all the buffers associated with the session.
899 However you need not do this if, after editing and re-compiling your
900 source code within Emacs, you wish continue debugging. When you
901 restart execution, GDB will automatically find your new executable.
902 Keeping the GUD buffer has the advantage of keeping the shell history
903 as well as GDB's breakpoints. You do need to check that the
904 breakpoints in recently edited source files are still in the right
908 @subsubsection Source Buffers
909 @cindex GDB commands in Fringe
911 @c @findex gdb-mouse-set-clear-breakpoint
912 @c @findex gdb-mouse-toggle-breakpoint
913 Many GDB commands can be entered using keybindings or the tool bar but
914 sometimes it is quicker to use the fringe. These commands either
915 manipulate breakpoints or control program execution. When there is no
916 fringe, you can use the margin but this is only present when the
917 source file already has a breakpoint.
919 You can click @kbd{Mouse-1} in the fringe or display margin of a
920 source buffer to set a breakpoint there and, on a graphical display, a
921 red bullet will appear on that line. If a breakpoint already exists
922 on that line, the same click will remove it. You can also enable or
923 disable a breakpoint by clicking @kbd{C-Mouse-1} on the bullet.
925 A solid arrow in the left fringe of a source buffer indicates the line
926 of the innermost frame where the debugged program has stopped. A
927 hollow arrow indicates the current execution line of higher level
930 If you drag the arrow in the fringe with @kbd{Mouse-1}
931 (@code{gdb-mouse-until}), execution will continue to the line where
932 you release the button, provided it is still in the same frame.
933 Alternatively, you can click @kbd{Mouse-3} at some point in the fringe
934 of this buffer and execution will advance to there. A similar command
935 (@code{gdb-mouse-jump}) allows you to jump to a source line without
936 executing the intermediate lines by clicking @kbd{C-Mouse-3}. This
937 command allows you to go backwards which can be useful for running
938 through code that has already executed, in order to examine its
939 execution in more detail.
943 Set or clear a breakpoint.
946 Enable or disable a breakpoint.
949 Continue execution to here.
955 If the variable @code{gdb-find-source-frame} is non-@code{nil} and
956 execution stops in a frame for which there is no source code e.g after
957 an interrupt, then Emacs finds and displays the first frame further up
958 stack for which there is source. If it is @code{nil} then the source
959 buffer continues to display the last frame which maybe more useful,
960 for example, when re-setting a breakpoint.
962 @node Breakpoints Buffer
963 @subsubsection Breakpoints Buffer
965 The breakpoints buffer shows the existing breakpoints and
966 watchpoints (@pxref{Breakpoints,,, gdb, The GNU debugger}). It has
967 these special commands, which mostly apply to the @dfn{current
968 breakpoint}, the breakpoint which point is on.
972 @kindex SPC @r{(GDB breakpoints buffer)}
973 @findex gdb-toggle-breakpoint
974 Enable/disable the current breakpoint (@code{gdb-toggle-breakpoint}).
975 On a graphical display, this changes the color of a bullet in the
976 margin of a source buffer at the relevant line. This is red when
977 the breakpoint is enabled and grey when it is disabled. Text-only
978 terminals correspondingly display a @samp{B} or @samp{b}.
981 @kindex D @r{(GDB breakpoints buffer)}
982 @findex gdb-delete-breakpoint
983 Delete the current breakpoint (@code{gdb-delete-breakpoint}).
986 @kindex RET @r{(GDB breakpoints buffer)}
987 @findex gdb-goto-breakpoint
988 Visit the source line for the current breakpoint
989 (@code{gdb-goto-breakpoint}).
992 @kindex Mouse-2 @r{(GDB breakpoints buffer)}
993 Visit the source line for the breakpoint you click on.
997 @subsubsection Stack Buffer
999 The stack buffer displays a @dfn{call stack}, with one line for each
1000 of the nested subroutine calls (@dfn{stack frames}) now active in the
1001 program. @xref{Backtrace,, Backtraces, gdb, The GNU debugger}.
1003 @findex gdb-frames-select
1004 An arrow in the fringe points to the selected frame or, if the fringe is
1005 not present, the number of the selected frame is displayed in reverse
1006 contrast. To select a frame in GDB, move point in the stack buffer to
1007 that stack frame and type @key{RET} (@code{gdb-frames-select}), or click
1008 @kbd{Mouse-2} on a stack frame. If the locals buffer is visible,
1009 selecting a stack frame updates it to display the local variables of the
1012 @node Other GDB-UI Buffers
1013 @subsubsection Other Buffers
1016 @item Input/Output Buffer
1017 @vindex gdb-use-separate-io-buffer
1018 If the variable @code{gdb-use-separate-io-buffer} is non-@code{nil},
1019 the program being debugged takes its input and displays its output
1020 here. Otherwise it uses the GUD buffer for that. To toggle whether
1021 GUD mode uses this buffer, do @kbd{M-x gdb-use-separate-io-buffer}.
1022 This takes effect when you next restart the program you are debugging.
1024 The history and replay commands from Shell mode are available here,
1025 as are the commands to send signals to the debugged program.
1029 The locals buffer displays the values of local variables of the
1030 current frame for simple data types (@pxref{Frame Info, Frame Info,
1031 Information on a frame, gdb, The GNU debugger}). Press @key{RET} or
1032 click @kbd{Mouse-2} on the value if you want to edit it.
1034 Arrays and structures display their type only. With GDB 6.4 or later,
1035 move point to their name and press @key{RET}, or alternatively click
1036 @kbd{Mouse-2} there, to examine their values. With earlier versions
1037 of GDB, use @kbd{Mouse-2} or @key{RET} on the type description
1038 (@samp{[struct/union]} or @samp{[array]}). @xref{Watch Expressions}.
1040 @item Registers Buffer
1041 @findex toggle-gdb-all-registers
1042 The registers buffer displays the values held by the registers
1043 (@pxref{Registers,,, gdb, The GNU debugger}). Press @key{RET} or
1044 click @kbd{Mouse-2} on a register if you want to edit its value.
1045 With GDB 6.4 or later, recently changed register values display with
1046 @code{font-lock-warning-face}. With earlier versions of GDB, you can
1047 press @key{SPC} to toggle the display of floating point registers
1048 (@code{toggle-gdb-all-registers}).
1050 @item Assembler Buffer
1051 The assembler buffer displays the current frame as machine code. An
1052 arrow points to the current instruction, and you can set and remove
1053 breakpoints as in a source buffer. Breakpoint icons also appear in
1054 the fringe or margin.
1056 @item Threads Buffer
1057 @findex gdb-threads-select
1058 The threads buffer displays a summary of all threads currently in your
1059 program (@pxref{Threads, Threads, Debugging programs with multiple
1060 threads, gdb, The GNU debugger}). Move point to any thread in the
1061 list and press @key{RET} to select it (@code{gdb-threads-select}) and
1062 display the associated source in the primary source buffer.
1063 Alternatively, click @kbd{Mouse-2} on a thread to select it. If the
1064 locals buffer is visible, its contents update to display the variables
1065 that are local in the new thread.
1068 The memory buffer lets you examine sections of program memory
1069 (@pxref{Memory, Memory, Examining memory, gdb, The GNU debugger}).
1070 Click @kbd{Mouse-1} on the appropriate part of the header line to
1071 change the starting address or number of data items that the buffer
1072 displays. Click @kbd{Mouse-3} on the header line to select the
1073 display format or unit size for these data items.
1076 @node Watch Expressions
1077 @subsubsection Watch Expressions
1078 @cindex Watching expressions in GDB
1081 @kindex C-x C-a C-w @r{(GUD)}
1082 If you want to see how a variable changes each time your program
1083 stops, move point into the variable name and click on the watch icon
1084 in the tool bar (@code{gud-watch}) or type @kbd{C-x C-a C-w}. If you
1085 specify a prefix argument, you can enter the variable name in the
1088 Each watch expression is displayed in the speedbar. Complex data
1089 types, such as arrays, structures and unions are represented in a tree
1090 format. Leaves and simple data types show the name of the expression
1091 and its value and, when the speedbar frame is selected, display the
1092 type as a tooltip. Higher levels show the name, type and address
1093 value for pointers and just the name and type otherwise. Root expressions
1094 also display the frame address as a tooltip to help identify the frame
1095 in which they were defined.
1097 To expand or contract a complex data type, click @kbd{Mouse-2}
1098 on the tag to the left of the expression.
1100 @kindex D @r{(GDB speedbar)}
1101 @findex gdb-var-delete
1102 To delete a complex watch expression, move point to the root
1103 expression in the speedbar and type @kbd{D} (@code{gdb-var-delete}).
1105 @kindex RET @r{(GDB speedbar)}
1106 @findex gdb-edit-value
1107 To edit a variable with a simple data type, or a simple element of a
1108 complex data type, move point there in the speedbar and type @key{RET}
1109 (@code{gdb-edit-value}). Or you can click @kbd{Mouse-2} on a value to
1110 edit it. Either way, this reads the new value using the minibuffer.
1112 @vindex gdb-show-changed-values
1113 If you set the variable @code{gdb-show-changed-values} to
1114 non-@code{nil} (the default value), Emacs uses
1115 @code{font-lock-warning-face} to highlight values that have recently
1116 changed and @code{shadow} face to make variables which have gone out of
1117 scope less noticeable. When a variable goes out of scope you can't
1120 @vindex gdb-use-colon-colon-notation
1121 If the variable @code{gdb-use-colon-colon-notation} is
1122 non-@code{nil}, Emacs uses the @samp{@var{function}::@var{variable}}
1123 format. This allows the user to display watch expressions which share
1124 the same variable name. The default value is @code{nil}.
1126 @vindex gdb-speedbar-auto-raise
1127 To automatically raise the speedbar every time the display of watch
1128 expressions updates, set @code{gdb-speedbar-auto-raise} to
1129 non-@code{nil}. This can be useful if you are debugging with a full
1132 @node Executing Lisp
1133 @section Executing Lisp Expressions
1135 Emacs has several different major modes for Lisp and Scheme. They are
1136 the same in terms of editing commands, but differ in the commands for
1137 executing Lisp expressions. Each mode has its own purpose.
1140 @item Emacs-Lisp mode
1141 The mode for editing source files of programs to run in Emacs Lisp.
1142 This mode defines @kbd{C-M-x} to evaluate the current defun.
1143 @xref{Lisp Libraries}.
1144 @item Lisp Interaction mode
1145 The mode for an interactive session with Emacs Lisp. It defines
1146 @kbd{C-j} to evaluate the sexp before point and insert its value in the
1147 buffer. @xref{Lisp Interaction}.
1149 The mode for editing source files of programs that run in Lisps other
1150 than Emacs Lisp. This mode defines @kbd{C-M-x} to send the current defun
1151 to an inferior Lisp process. @xref{External Lisp}.
1152 @item Inferior Lisp mode
1153 The mode for an interactive session with an inferior Lisp process.
1154 This mode combines the special features of Lisp mode and Shell mode
1155 (@pxref{Shell Mode}).
1157 Like Lisp mode but for Scheme programs.
1158 @item Inferior Scheme mode
1159 The mode for an interactive session with an inferior Scheme process.
1162 Most editing commands for working with Lisp programs are in fact
1163 available globally. @xref{Programs}.
1165 @node Lisp Libraries
1166 @section Libraries of Lisp Code for Emacs
1168 @cindex loading Lisp code
1170 Lisp code for Emacs editing commands is stored in files whose names
1171 conventionally end in @file{.el}. This ending tells Emacs to edit them in
1172 Emacs-Lisp mode (@pxref{Executing Lisp}).
1175 Emacs Lisp code can be compiled into byte-code, which loads faster,
1176 takes up less space, and executes faster. @xref{Byte Compilation,,
1177 Byte Compilation, elisp, the Emacs Lisp Reference Manual}. By
1178 convention, the compiled code for a library goes in a separate file
1179 whose name ends in @samp{.elc}. Thus, the compiled code for
1180 @file{foo.el} goes in @file{foo.elc}.
1183 To execute a file of Emacs Lisp code, use @kbd{M-x load-file}. This
1184 command reads a file name using the minibuffer and then executes the
1185 contents of that file as Lisp code. It is not necessary to visit the
1186 file first; in any case, this command reads the file as found on disk,
1187 not text in an Emacs buffer.
1190 @findex load-library
1191 Once a file of Lisp code is installed in the Emacs Lisp library
1192 directories, users can load it using @kbd{M-x load-library}. Programs
1193 can load it by calling @code{load}, a more primitive function that is
1194 similar but accepts some additional arguments.
1196 @kbd{M-x load-library} differs from @kbd{M-x load-file} in that it
1197 searches a sequence of directories and tries three file names in each
1198 directory. Suppose your argument is @var{lib}; the three names are
1199 @file{@var{lib}.elc}, @file{@var{lib}.el}, and lastly just
1200 @file{@var{lib}}. If @file{@var{lib}.elc} exists, it is by convention
1201 the result of compiling @file{@var{lib}.el}; it is better to load the
1202 compiled file, since it will load and run faster.
1204 If @code{load-library} finds that @file{@var{lib}.el} is newer than
1205 @file{@var{lib}.elc} file, it issues a warning, because it's likely
1206 that somebody made changes to the @file{.el} file and forgot to
1207 recompile it. Nonetheless, it loads @file{@var{lib}.elc}. This is
1208 because people often leave unfinished edits the source file, and don't
1209 recompile it until they think it is ready to use.
1211 Because the argument to @code{load-library} is usually not in itself
1212 a valid file name, file name completion is not available. Indeed, when
1213 using this command, you usually do not know exactly what file name
1217 The sequence of directories searched by @kbd{M-x load-library} is
1218 specified by the variable @code{load-path}, a list of strings that are
1219 directory names. The default value of the list contains the directories where
1220 the Lisp code for Emacs itself is stored. If you have libraries of
1221 your own, put them in a single directory and add that directory
1222 to @code{load-path}. @code{nil} in this list stands for the current default
1223 directory, but it is probably not a good idea to put @code{nil} in the
1224 list. If you find yourself wishing that @code{nil} were in the list,
1225 most likely what you really want to do is use @kbd{M-x load-file}
1229 Often you do not have to give any command to load a library, because
1230 the commands defined in the library are set up to @dfn{autoload} that
1231 library. Trying to run any of those commands calls @code{load} to load
1232 the library; this replaces the autoload definitions with the real ones
1235 @vindex load-dangerous-libraries
1236 @cindex Lisp files byte-compiled by XEmacs
1237 By default, Emacs refuses to load compiled Lisp files which were
1238 compiled with XEmacs, a modified versions of Emacs---they can cause
1239 Emacs to crash. Set the variable @code{load-dangerous-libraries} to
1240 @code{t} if you want to try loading them.
1243 @section Evaluating Emacs Lisp Expressions
1244 @cindex Emacs-Lisp mode
1245 @cindex mode, Emacs-Lisp
1247 @findex emacs-lisp-mode
1248 Lisp programs intended to be run in Emacs should be edited in
1249 Emacs-Lisp mode; this happens automatically for file names ending in
1250 @file{.el}. By contrast, Lisp mode itself is used for editing Lisp
1251 programs intended for other Lisp systems. To switch to Emacs-Lisp mode
1252 explicitly, use the command @kbd{M-x emacs-lisp-mode}.
1254 For testing of Lisp programs to run in Emacs, it is often useful to
1255 evaluate part of the program as it is found in the Emacs buffer. For
1256 example, after changing the text of a Lisp function definition,
1257 evaluating the definition installs the change for future calls to the
1258 function. Evaluation of Lisp expressions is also useful in any kind of
1259 editing, for invoking noninteractive functions (functions that are
1264 Read a single Lisp expression in the minibuffer, evaluate it, and print
1265 the value in the echo area (@code{eval-expression}).
1267 Evaluate the Lisp expression before point, and print the value in the
1268 echo area (@code{eval-last-sexp}).
1270 Evaluate the defun containing or after point, and print the value in
1271 the echo area (@code{eval-defun}).
1272 @item M-x eval-region
1273 Evaluate all the Lisp expressions in the region.
1274 @item M-x eval-buffer
1275 Evaluate all the Lisp expressions in the buffer.
1279 @c This uses ``colon'' instead of a literal `:' because Info cannot
1280 @c cope with a `:' in a menu
1281 @kindex M-@key{colon}
1286 @findex eval-expression
1287 @kbd{M-:} (@code{eval-expression}) is the most basic command for evaluating
1288 a Lisp expression interactively. It reads the expression using the
1289 minibuffer, so you can execute any expression on a buffer regardless of
1290 what the buffer contains. When the expression is evaluated, the current
1291 buffer is once again the buffer that was current when @kbd{M-:} was
1294 @kindex C-M-x @r{(Emacs-Lisp mode)}
1296 In Emacs-Lisp mode, the key @kbd{C-M-x} is bound to the command
1297 @code{eval-defun}, which parses the defun containing or following point
1298 as a Lisp expression and evaluates it. The value is printed in the echo
1299 area. This command is convenient for installing in the Lisp environment
1300 changes that you have just made in the text of a function definition.
1302 @kbd{C-M-x} treats @code{defvar} expressions specially. Normally,
1303 evaluating a @code{defvar} expression does nothing if the variable it
1304 defines already has a value. But @kbd{C-M-x} unconditionally resets the
1305 variable to the initial value specified in the @code{defvar} expression.
1306 @code{defcustom} expressions are treated similarly.
1307 This special feature is convenient for debugging Lisp programs.
1308 Typing @kbd{C-M-x} on a @code{defface} expression reinitializes
1309 the face according to the @code{defface} specification.
1312 @findex eval-last-sexp
1313 The command @kbd{C-x C-e} (@code{eval-last-sexp}) evaluates the Lisp
1314 expression preceding point in the buffer, and displays the value in the
1315 echo area. It is available in all major modes, not just Emacs-Lisp
1316 mode. It does not treat @code{defvar} specially.
1318 When the result of an evaluation is an integer, you can type
1319 @kbd{C-x C-e} a second time to display the value of the integer result
1320 in additional formats (octal, hexadecimal, and character).
1322 If @kbd{C-x C-e}, or @kbd{M-:} is given a numeric argument, it
1323 inserts the value into the current buffer at point, rather than
1324 displaying it in the echo area. The argument's value does not matter.
1325 @kbd{C-M-x} with a numeric argument instruments the function
1326 definition for Edebug (@pxref{Instrumenting, Instrumenting for Edebug,, elisp, the Emacs Lisp Reference Manual}).
1330 The most general command for evaluating Lisp expressions from a buffer
1331 is @code{eval-region}. @kbd{M-x eval-region} parses the text of the
1332 region as one or more Lisp expressions, evaluating them one by one.
1333 @kbd{M-x eval-buffer} is similar but evaluates the entire
1334 buffer. This is a reasonable way to install the contents of a file of
1335 Lisp code that you are ready to test. Later, as you find bugs and
1336 change individual functions, use @kbd{C-M-x} on each function that you
1337 change. This keeps the Lisp world in step with the source file.
1339 @vindex eval-expression-print-level
1340 @vindex eval-expression-print-length
1341 @vindex eval-expression-debug-on-error
1342 The two customizable variables @code{eval-expression-print-level} and
1343 @code{eval-expression-print-length} control the maximum depth and length
1344 of lists to print in the result of the evaluation commands before
1345 abbreviating them. @code{eval-expression-debug-on-error} controls
1346 whether evaluation errors invoke the debugger when these commands are
1347 used; its default is @code{t}.
1349 @node Lisp Interaction
1350 @section Lisp Interaction Buffers
1352 The buffer @samp{*scratch*} which is selected when Emacs starts up is
1353 provided for evaluating Lisp expressions interactively inside Emacs.
1355 The simplest way to use the @samp{*scratch*} buffer is to insert Lisp
1356 expressions and type @kbd{C-j} after each expression. This command
1357 reads the Lisp expression before point, evaluates it, and inserts the
1358 value in printed representation before point. The result is a complete
1359 typescript of the expressions you have evaluated and their values.
1361 The @samp{*scratch*} buffer's major mode is Lisp Interaction mode, which
1362 is the same as Emacs-Lisp mode except for the binding of @kbd{C-j}.
1364 @findex lisp-interaction-mode
1365 The rationale for this feature is that Emacs must have a buffer when
1366 it starts up, but that buffer is not useful for editing files since a
1367 new buffer is made for every file that you visit. The Lisp interpreter
1368 typescript is the most useful thing I can think of for the initial
1369 buffer to do. Type @kbd{M-x lisp-interaction-mode} to put the current
1370 buffer in Lisp Interaction mode.
1373 An alternative way of evaluating Emacs Lisp expressions interactively
1374 is to use Inferior Emacs-Lisp mode, which provides an interface rather
1375 like Shell mode (@pxref{Shell Mode}) for evaluating Emacs Lisp
1376 expressions. Type @kbd{M-x ielm} to create an @samp{*ielm*} buffer
1377 which uses this mode. For more information see that command's
1381 @section Running an External Lisp
1383 Emacs has facilities for running programs in other Lisp systems. You can
1384 run a Lisp process as an inferior of Emacs, and pass expressions to it to
1385 be evaluated. You can also pass changed function definitions directly from
1386 the Emacs buffers in which you edit the Lisp programs to the inferior Lisp
1390 @vindex inferior-lisp-program
1392 To run an inferior Lisp process, type @kbd{M-x run-lisp}. This runs
1393 the program named @code{lisp}, the same program you would run by typing
1394 @code{lisp} as a shell command, with both input and output going through
1395 an Emacs buffer named @samp{*lisp*}. That is to say, any ``terminal
1396 output'' from Lisp will go into the buffer, advancing point, and any
1397 ``terminal input'' for Lisp comes from text in the buffer. (You can
1398 change the name of the Lisp executable file by setting the variable
1399 @code{inferior-lisp-program}.)
1401 To give input to Lisp, go to the end of the buffer and type the input,
1402 terminated by @key{RET}. The @samp{*lisp*} buffer is in Inferior Lisp
1403 mode, which combines the special characteristics of Lisp mode with most
1404 of the features of Shell mode (@pxref{Shell Mode}). The definition of
1405 @key{RET} to send a line to a subprocess is one of the features of Shell
1409 For the source files of programs to run in external Lisps, use Lisp
1410 mode. You can switch to this mode with @kbd{M-x lisp-mode}, and it is
1411 used automatically for files whose names end in @file{.l},
1412 @file{.lsp}, or @file{.lisp}.
1414 @kindex C-M-x @r{(Lisp mode)}
1415 @findex lisp-eval-defun
1416 When you edit a function in a Lisp program you are running, the easiest
1417 way to send the changed definition to the inferior Lisp process is the key
1418 @kbd{C-M-x}. In Lisp mode, this runs the function @code{lisp-eval-defun},
1419 which finds the defun around or following point and sends it as input to
1420 the Lisp process. (Emacs can send input to any inferior process regardless
1421 of what buffer is current.)
1423 Contrast the meanings of @kbd{C-M-x} in Lisp mode (for editing
1424 programs to be run in another Lisp system) and Emacs-Lisp mode (for
1425 editing Lisp programs to be run in Emacs; see @pxref{Lisp Eval}): in
1426 both modes it has the effect of installing the function definition
1427 that point is in, but the way of doing so is different according to
1428 where the relevant Lisp environment is found.
1432 arch-tag: 9c3c2f71-b332-4144-8500-3ff9945a50ed