V. Compiling and Testing Programs
The previous chapter discusses the Emacs commands that are useful for
making changes in programs. This chapter deals with commands that assist
in the larger process of developing and maintaining programs.
V.1 Running Compilations under Emacs
Emacs can run compilers for noninteractive languages such as C and
Fortran as inferior processes, feeding the error log into an Emacs buffer.
It can also parse the error messages and show you the source lines where
compilation errors occurred.
- M-x compile
- Run a compiler asynchronously under Emacs, with error messages going to
the `*compilation*' buffer.
- M-x recompile
- Invoke a compiler with the same command as in the last invocation of
M-x compile.
- M-x grep
- Run
grep asynchronously under Emacs, with matching lines
listed in the buffer named `*grep*'.
- M-x grep-find
- Run
grep via find, with user-specified arguments, and
collect output in the buffer named `*grep*'.
- M-x kill-compilation
- M-x kill-grep
- Kill the running compilation or
grep subprocess.
To run make or another compilation command, do M-x
compile. This command reads a shell command line using the minibuffer,
and then executes the command in an inferior shell, putting output in
the buffer named `*compilation*'. The current buffer's default
directory is used as the working directory for the execution of the
command; normally, therefore, the compilation happens in this
directory.
When the shell command line is read, the minibuffer appears containing
a default command line, which is the command you used the last time you
did M-x compile. If you type just RET, the same command
line is used again. For the first M-x compile, the default is
`make -k'. The default compilation command comes from the variable
compile-command; if the appropriate compilation command for a
file is something other than `make -k', it can be useful for the
file to specify a local value for compile-command (see section AD.2.5 Local Variables in Files).
Starting a compilation displays the buffer `*compilation*' in
another window but does not select it. The buffer's mode line tells you
whether compilation is finished, with the word `run' or `exit'
inside the parentheses. You do not have to keep this buffer visible;
compilation continues in any case. While a compilation is going on, the
string `Compiling' appears in the mode lines of all windows. When
this string disappears, the compilation is finished.
If you want to watch the compilation transcript as it appears, switch
to the `*compilation*' buffer and move point to the end of the
buffer. When point is at the end, new compilation output is inserted
above point, which remains at the end. If point is not at the end of
the buffer, it remains fixed while more compilation output is added at
the end of the buffer.
If you set the variable compilation-scroll-output to a
non-nil value, then the compilation buffer always scrolls to
follow output as it comes in.
To kill the compilation process, do M-x kill-compilation. When
the compiler process terminates, the mode line of the
`*compilation*' buffer changes to say `signal' instead of
`run'. Starting a new compilation also kills any running
compilation, as only one can exist at any time. However, M-x
compile asks for confirmation before actually killing a compilation
that is running.
To rerun the last compilation with the same command, type M-x
recompile. This automatically reuses the compilation command from the
last invocation of M-x compile.
V.2 Searching with Grep under Emacs
Just as you can run a compiler from Emacs and then visit the lines
where there were compilation errors, you can also run grep and
then visit the lines on which matches were found. This works by
treating the matches reported by grep as if they were "errors."
To do this, type M-x grep, then enter a command line that
specifies how to run grep. Use the same arguments you would give
grep when running it normally: a grep-style regexp
(usually in single-quotes to quote the shell's special characters)
followed by file names, which may use wildcards. The output from
grep goes in the `*grep*' buffer. You can find the
corresponding lines in the original files using C-x ` and
RET, as with compilation errors.
If you specify a prefix argument for M-x grep, it figures out
the tag (see section W.2 Tags Tables) around point, and puts that into the default
grep command.
The command M-x grep-find is similar to M-x grep, but it
supplies a different initial default for the command--one that runs
both find and grep, so as to search every file in a
directory tree. See also the find-grep-dired command,
in AB.15 Dired and find.
V.3 Compilation Mode
The `*compilation*' buffer uses a special major mode, Compilation
mode, whose main feature is to provide a convenient way to look at the
source line where the error happened.
If you set the variable compilation-scroll-output to a
non-nil value, then the compilation buffer always scrolls to
follow output as it comes in.
- C-x `
- Visit the locus of the next compiler error message or
grep match.
- RET
- Visit the locus of the error message that point is on.
This command is used in the compilation buffer.
- Mouse-2
- Visit the locus of the error message that you click on.
You can visit the source for any particular error message by moving
point in the `*compilation*' buffer to that error message and
typing RET (compile-goto-error). Alternatively, you can
click Mouse-2 on the error message; you need not switch to the
`*compilation*' buffer first.
To parse the compiler error messages sequentially, type C-x `
(next-error). The character following the C-x is the
backquote or "grave accent," not the single-quote. This command is
available in all buffers, not just in `*compilation*'; it displays
the next error message at the top of one window and source location of
the error in another window.
The first time C-x ` is used after the start of a compilation,
it moves to the first error's location. Subsequent uses of C-x `
advance down to subsequent errors. If you visit a specific error
message with RET or Mouse-2, subsequent C-x `
commands advance from there. When C-x ` gets to the end of the
buffer and finds no more error messages to visit, it fails and signals
an Emacs error.
C-u C-x ` starts scanning from the beginning of the compilation
buffer. This is one way to process the same set of errors again.
To parse messages from the compiler, Compilation mode uses the
variable compilation-error-regexp-alist which lists various
formats of error messages and tells Emacs how to extract the source file
and the line number from the text of a message. If your compiler isn't
supported, you can tailor Compilation mode to it by adding elements to
that list. A similar variable grep-regexp-alist tells Emacs how
to parse output of a grep command.
Compilation mode also redefines the keys SPC and DEL to
scroll by screenfuls, and M-n and M-p to move to the next or
previous error message. You can also use M-{ and M-} to
move up or down to an error message for a different source file.
The features of Compilation mode are also available in a minor mode
called Compilation Minor mode. This lets you parse error messages in
any buffer, not just a normal compilation output buffer. Type M-x
compilation-minor-mode to enable the minor mode. This defines the keys
RET and Mouse-2, as in the Compilation major mode.
Compilation minor mode works in any buffer, as long as the contents
are in a format that it understands. In an Rlogin buffer (see section AC.15.10 Remote Host Shell), Compilation minor mode automatically accesses remote source
files by FTP (see section M.1 File Names).
V.4 Subshells for Compilation
Emacs uses a shell to run the compilation command, but specifies
the option for a noninteractive shell. This means, in particular, that
the shell should start with no prompt. If you find your usual shell
prompt making an unsightly appearance in the `*compilation*'
buffer, it means you have made a mistake in your shell's init file by
setting the prompt unconditionally. (This init file's name may be
`.bashrc', `.profile', `.cshrc', `.shrc', or various
other things, depending on the shell you use.) The shell init file
should set the prompt only if there already is a prompt. In csh, here
is how to do it:
| | if ($?prompt) set prompt = ...
|
And here's how to do it in bash:
| | if [ "${PS1+set}" = set ]
then PS1=...
fi
|
There may well be other things that your shell's init file
ought to do only for an interactive shell. You can use the same
method to conditionalize them.
The MS-DOS "operating system" does not support asynchronous
subprocesses; to work around this lack, M-x compile runs the
compilation command synchronously on MS-DOS. As a consequence, you must
wait until the command finishes before you can do anything else in
Emacs. See section AH. Emacs and MS-DOS.
V.5 Running Debuggers Under Emacs
The GUD (Grand Unified Debugger) library provides an interface to
various symbolic debuggers from within Emacs. We recommend the debugger
GDB, which is free software, but you can also run DBX, SDB or XDB if you
have them. GUD can also serve as an interface to the Perl's debugging
mode, the Python debugger PDB, and to JDB, the Java Debugger.
See section `The Lisp Debugger' in the Emacs Lisp Reference Manual,
for information on debugging Emacs Lisp programs.
V.5.1 Starting GUD
There are several commands for starting a debugger, each corresponding
to a particular debugger program.
- M-x gdb RET file RET
-
Run GDB as a subprocess of Emacs. This command creates a buffer
for input and output to GDB, and switches to it. If a GDB buffer
already exists, it just switches to that buffer.
- M-x dbx RET file RET
-
Similar, but run DBX instead of GDB.
- M-x xdb RET file RET
-
Similar, but run XDB instead of GDB. Use the variable
gud-xdb-directories to specify directories to search for source
files.
- M-x sdb RET file RET
-
Similar, but run SDB instead of GDB.
Some versions of SDB do not mention source file names in their
messages. When you use them, you need to have a valid tags table
(see section W.2 Tags Tables) in order for GUD to find functions in the source code.
If you have not visited a tags table or the tags table doesn't list one
of the functions, you get a message saying `The sdb support
requires a valid tags table to work'. If this happens, generate a valid
tags table in the working directory and try again.
- M-x perldb RET file RET
-
Run the Perl interpreter in debug mode to debug file, a Perl program.
- M-x jdb RET file RET
-
Run the Java debugger to debug file.
- M-x pdb RET file RET
-
Run the Python debugger to debug file.
Each of these commands takes one argument: a command line to invoke
the debugger. In the simplest case, specify just the name of the
executable file you want to debug. You may also use options that the
debugger supports. However, shell wildcards and variables are not
allowed. GUD assumes that the first argument not starting with a
`-' is the executable file name.
Emacs can only run one debugger process at a time.
V.5.2 Debugger Operation
When you run a debugger with GUD, the debugger uses an Emacs buffer
for its ordinary input and output. This is called the GUD buffer. The
debugger displays the source files of the program by visiting them in
Emacs buffers. An arrow (`=>') in one of these buffers indicates
the current execution line.(12) Moving point in
this buffer does not move the arrow.
You can start editing these source files at any time in the buffers
that display them. The arrow is not part of the file's
text; it appears only on the screen. If you do modify a source file,
keep in mind that inserting or deleting lines will throw off the arrow's
positioning; GUD has no way of figuring out which line corresponded
before your changes to the line number in a debugger message. Also,
you'll typically have to recompile and restart the program for your
changes to be reflected in the debugger's tables.
If you wish, you can control your debugger process entirely through the
debugger buffer, which uses a variant of Shell mode. All the usual
commands for your debugger are available, and you can use the Shell mode
history commands to repeat them. See section AC.15.3 Shell Mode.
V.5.3 Commands of GUD
The GUD interaction buffer uses a variant of Shell mode, so the
commands of Shell mode are available (see section AC.15.3 Shell Mode). GUD mode
also provides commands for setting and clearing breakpoints, for
selecting stack frames, and for stepping through the program. These
commands are available both in the GUD buffer and globally, but with
different key bindings.
The breakpoint commands are normally used in source file buffers,
because that is the easiest way to specify where to set or clear the
breakpoint. Here's the global command to set a breakpoint:
- C-x SPC
-
Set a breakpoint on the source line that point is on.
Here are the other special commands provided by GUD. The keys
starting with C-c are available only in the GUD interaction
buffer. The key bindings that start with C-x C-a are available in
the GUD interaction buffer and also in source files.
- C-c C-l
-
- C-x C-a C-l
-
Display in another window the last line referred to in the GUD
buffer (that is, the line indicated in the last location message).
This runs the command
gud-refresh.
- C-c C-s
-
- C-x C-a C-s
-
Execute a single line of code (
gud-step). If the line contains
a function call, execution stops after entering the called function.
- C-c C-n
-
- C-x C-a C-n
-
Execute a single line of code, stepping across entire function calls
at full speed (
gud-next).
- C-c C-i
-
- C-x C-a C-i
-
Execute a single machine instruction (
gud-stepi).
- C-c C-r
-
- C-x C-a C-r
-
Continue execution without specifying any stopping point. The program
will run until it hits a breakpoint, terminates, or gets a signal that
the debugger is checking for (
gud-cont).
- C-c C-d
-
- C-x C-a C-d
-
Delete the breakpoint(s) on the current source line, if any
(
gud-remove). If you use this command in the GUD interaction
buffer, it applies to the line where the program last stopped.
- C-c C-t
-
- C-x C-a C-t
-
Set a temporary breakpoint on the current source line, if any.
If you use this command in the GUD interaction buffer,
it applies to the line where the program last stopped.
The above commands are common to all supported debuggers. If you are
using GDB or (some versions of) DBX, these additional commands are available:
- C-c <
-
- C-x C-a <
-
Select the next enclosing stack frame (
gud-up). This is
equivalent to the `up' command.
- C-c >
-
- C-x C-a >
-
Select the next inner stack frame (
gud-down). This is
equivalent to the `down' command.
If you are using GDB, these additional key bindings are available:
- TAB
-
With GDB, complete a symbol name (
gud-gdb-complete-command).
This key is available only in the GUD interaction buffer, and requires
GDB versions 4.13 and later.
- C-c C-f
-
- C-x C-a C-f
-
Run the program until the selected stack frame returns (or until it
stops for some other reason).
These commands interpret a numeric argument as a repeat count, when
that makes sense.
Because TAB serves as a completion command, you can't use it to
enter a tab as input to the program you are debugging with GDB.
Instead, type C-q TAB to enter a tab.
V.5.4 GUD Customization
On startup, GUD runs one of the following hooks: gdb-mode-hook,
if you are using GDB; dbx-mode-hook, if you are using DBX;
sdb-mode-hook, if you are using SDB; xdb-mode-hook, if you
are using XDB; perldb-mode-hook, for Perl debugging mode;
pdb-mode-hook, for PDB; jdb-mode-hook, for JDB. You can
use these hooks to define custom key bindings for the debugger
interaction buffer. See section AD.2.3 Hooks.
Here is a convenient way to define a command that sends a particular
command string to the debugger, and set up a key binding for it in the
debugger interaction buffer:
| | (gud-def function cmdstring binding docstring)
|
This defines a command named function which sends
cmdstring to the debugger process, and gives it the documentation
string docstring. You can then use the command function in any
buffer. If binding is non-nil, gud-def also binds
the command to C-c binding in the GUD buffer's mode and to
C-x C-a binding generally.
The command string cmdstring may contain certain
`%'-sequences that stand for data to be filled in at the time
function is called:
- `%f'
- The name of the current source file. If the current buffer is the GUD
buffer, then the "current source file" is the file that the program
stopped in.
- `%l'
- The number of the current source line. If the current buffer is the GUD
buffer, then the "current source line" is the line that the program
stopped in.
- `%e'
- The text of the C lvalue or function-call expression at or adjacent to point.
- `%a'
- The text of the hexadecimal address at or adjacent to point.
- `%p'
- The numeric argument of the called function, as a decimal number. If
the command is used without a numeric argument, `%p' stands for the
empty string.
If you don't use `%p' in the command string, the command you define
ignores any numeric argument.
V.5.5 GUD Tooltips
The Tooltip facility (see section P.18 Tooltips (or "Balloon Help")) provides support for GUD. If
GUD support is activated by customizing the tooltip group,
variable values can be displayed in tooltips by pointing at them with
the mouse in the GUD buffer or in source buffers with major modes in the
customizable list tooltip-gud-modes.
V.6 Executing Lisp Expressions
Emacs has several different major modes for Lisp and Scheme. They are
the same in terms of editing commands, but differ in the commands for
executing Lisp expressions. Each mode has its own purpose.
- Emacs-Lisp mode
- The mode for editing source files of programs to run in Emacs Lisp.
This mode defines C-M-x to evaluate the current defun.
See section V.7 Libraries of Lisp Code for Emacs.
- Lisp Interaction mode
- The mode for an interactive session with Emacs Lisp. It defines
C-j to evaluate the sexp before point and insert its value in the
buffer. See section V.9 Lisp Interaction Buffers.
- Lisp mode
- The mode for editing source files of programs that run in Lisps other
than Emacs Lisp. This mode defines C-M-x to send the current defun
to an inferior Lisp process. See section V.10 Running an External Lisp.
- Inferior Lisp mode
- The mode for an interactive session with an inferior Lisp process.
This mode combines the special features of Lisp mode and Shell mode
(see section AC.15.3 Shell Mode).
- Scheme mode
- Like Lisp mode but for Scheme programs.
- Inferior Scheme mode
- The mode for an interactive session with an inferior Scheme process.
Most editing commands for working with Lisp programs are in fact
available globally. See section U. Editing Programs.
V.7 Libraries of Lisp Code for Emacs
Lisp code for Emacs editing commands is stored in files whose names
conventionally end in `.el'. This ending tells Emacs to edit them in
Emacs-Lisp mode (see section V.6 Executing Lisp Expressions).
To execute a file of Emacs Lisp code, use M-x load-file. This
command reads a file name using the minibuffer and then executes the
contents of that file as Lisp code. It is not necessary to visit the
file first; in any case, this command reads the file as found on disk,
not text in an Emacs buffer.
Once a file of Lisp code is installed in the Emacs Lisp library
directories, users can load it using M-x load-library. Programs can
load it by calling load-library, or with load, a more primitive
function that is similar but accepts some additional arguments.
M-x load-library differs from M-x load-file in that it
searches a sequence of directories and tries three file names in each
directory. Suppose your argument is lib; the three names are
`lib.elc', `lib.el', and lastly just
`lib'. If `lib.elc' exists, it is by convention
the result of compiling `lib.el'; it is better to load the
compiled file, since it will load and run faster.
If load-library finds that `lib.el' is newer than
`lib.elc' file, it issues a warning, because it's likely that
somebody made changes to the `.el' file and forgot to recompile
it.
Because the argument to load-library is usually not in itself
a valid file name, file name completion is not available. Indeed, when
using this command, you usually do not know exactly what file name
will be used.
The sequence of directories searched by M-x load-library is
specified by the variable load-path, a list of strings that are
directory names. The default value of the list contains the directory where
the Lisp code for Emacs itself is stored. If you have libraries of
your own, put them in a single directory and add that directory
to load-path. nil in this list stands for the current default
directory, but it is probably not a good idea to put nil in the
list. If you find yourself wishing that nil were in the list,
most likely what you really want to do is use M-x load-file
this once.
Often you do not have to give any command to load a library, because
the commands defined in the library are set up to autoload that
library. Trying to run any of those commands calls load to load
the library; this replaces the autoload definitions with the real ones
from the library.
Emacs Lisp code can be compiled into byte-code which loads faster,
takes up less space when loaded, and executes faster. See section `Byte Compilation' in the Emacs Lisp Reference Manual.
By convention, the compiled code for a library goes in a separate file
whose name consists of the library source file with `c' appended.
Thus, the compiled code for `foo.el' goes in `foo.elc'.
That's why load-library searches for `.elc' files first.
By default, Emacs refuses to load compiled Lisp files which were
compiled with XEmacs, a modified versions of Emacs--they can cause
Emacs to crash. Set the variable load-dangerous-libraries to
t if you want to try loading them.
V.8 Evaluating Emacs-Lisp Expressions
Lisp programs intended to be run in Emacs should be edited in
Emacs-Lisp mode; this happens automatically for file names ending in
`.el'. By contrast, Lisp mode itself is used for editing Lisp
programs intended for other Lisp systems. To switch to Emacs-Lisp mode
explicitly, use the command M-x emacs-lisp-mode.
For testing of Lisp programs to run in Emacs, it is often useful to
evaluate part of the program as it is found in the Emacs buffer. For
example, after changing the text of a Lisp function definition,
evaluating the definition installs the change for future calls to the
function. Evaluation of Lisp expressions is also useful in any kind of
editing, for invoking noninteractive functions (functions that are
not commands).
- M-:
- Read a single Lisp expression in the minibuffer, evaluate it, and print
the value in the echo area (
eval-expression).
- C-x C-e
- Evaluate the Lisp expression before point, and print the value in the
echo area (
eval-last-sexp).
- C-M-x
- Evaluate the defun containing or after point, and print the value in
the echo area (
eval-defun).
- M-x eval-region
- Evaluate all the Lisp expressions in the region.
- M-x eval-current-buffer
- Evaluate all the Lisp expressions in the buffer.
M-: (eval-expression) is the most basic command for evaluating
a Lisp expression interactively. It reads the expression using the
minibuffer, so you can execute any expression on a buffer regardless of
what the buffer contains. When the expression is evaluated, the current
buffer is once again the buffer that was current when M-: was
typed.
In Emacs-Lisp mode, the key C-M-x is bound to the command
eval-defun, which parses the defun containing or following point
as a Lisp expression and evaluates it. The value is printed in the echo
area. This command is convenient for installing in the Lisp environment
changes that you have just made in the text of a function definition.
C-M-x treats defvar expressions specially. Normally,
evaluating a defvar expression does nothing if the variable it
defines already has a value. But C-M-x unconditionally resets the
variable to the initial value specified in the defvar expression.
defcustom expressions are treated similarly.
This special feature is convenient for debugging Lisp programs.
The command C-x C-e (eval-last-sexp) evaluates the Lisp
expression preceding point in the buffer, and displays the value in the
echo area. It is available in all major modes, not just Emacs-Lisp
mode. It does not treat defvar specially.
If C-M-x, C-x C-e, or M-: is given a numeric
argument, it inserts the value into the current buffer at point, rather
than displaying it in the echo area. The argument's value does not
matter.
The most general command for evaluating Lisp expressions from a buffer
is eval-region. M-x eval-region parses the text of the
region as one or more Lisp expressions, evaluating them one by one.
M-x eval-current-buffer is similar but evaluates the entire
buffer. This is a reasonable way to install the contents of a file of
Lisp code that you are ready to test. Later, as you find bugs and
change individual functions, use C-M-x on each function that you
change. This keeps the Lisp world in step with the source file.
The customizable variables eval-expression-print-level and
eval-expression-print-length control the maximum depth and length
of lists to print in the result of the evaluation commands before
abbreviating them. eval-expression-debug-on-error controls
whether evaluation errors invoke the debugger when these commands are
used.
V.9 Lisp Interaction Buffers
The buffer `*scratch*' which is selected when Emacs starts up is
provided for evaluating Lisp expressions interactively inside Emacs.
The simplest way to use the `*scratch*' buffer is to insert Lisp
expressions and type C-j after each expression. This command
reads the Lisp expression before point, evaluates it, and inserts the
value in printed representation before point. The result is a complete
typescript of the expressions you have evaluated and their values.
The `*scratch*' buffer's major mode is Lisp Interaction mode, which
is the same as Emacs-Lisp mode except for the binding of C-j.
The rationale for this feature is that Emacs must have a buffer when
it starts up, but that buffer is not useful for editing files since a
new buffer is made for every file that you visit. The Lisp interpreter
typescript is the most useful thing I can think of for the initial
buffer to do. Type M-x lisp-interaction-mode to put the current
buffer in Lisp Interaction mode.
An alternative way of evaluating Emacs Lisp expressions interactively
is to use Inferior Emacs-Lisp mode, which provides an interface rather
like Shell mode (see section AC.15.3 Shell Mode) for evaluating Emacs Lisp
expressions. Type M-x ielm to create an `*ielm*' buffer
which uses this mode.
V.10 Running an External Lisp
Emacs has facilities for running programs in other Lisp systems. You can
run a Lisp process as an inferior of Emacs, and pass expressions to it to
be evaluated. You can also pass changed function definitions directly from
the Emacs buffers in which you edit the Lisp programs to the inferior Lisp
process.
To run an inferior Lisp process, type M-x run-lisp. This runs
the program named lisp, the same program you would run by typing
lisp as a shell command, with both input and output going through
an Emacs buffer named `*lisp*'. That is to say, any "terminal
output" from Lisp will go into the buffer, advancing point, and any
"terminal input" for Lisp comes from text in the buffer. (You can
change the name of the Lisp executable file by setting the variable
inferior-lisp-program.)
To give input to Lisp, go to the end of the buffer and type the input,
terminated by RET. The `*lisp*' buffer is in Inferior Lisp
mode, which combines the special characteristics of Lisp mode with most
of the features of Shell mode (see section AC.15.3 Shell Mode). The definition of
RET to send a line to a subprocess is one of the features of Shell
mode.
For the source files of programs to run in external Lisps, use Lisp
mode. This mode can be selected with M-x lisp-mode, and is used
automatically for files whose names end in `.l', `.lsp', or
`.lisp', as most Lisp systems usually expect.
When you edit a function in a Lisp program you are running, the easiest
way to send the changed definition to the inferior Lisp process is the key
C-M-x. In Lisp mode, this runs the function lisp-eval-defun,
which finds the defun around or following point and sends it as input to
the Lisp process. (Emacs can send input to any inferior process regardless
of what buffer is current.)
Contrast the meanings of C-M-x in Lisp mode (for editing programs
to be run in another Lisp system) and Emacs-Lisp mode (for editing Lisp
programs to be run in Emacs): in both modes it has the effect of installing
the function definition that point is in, but the way of doing so is
different according to where the relevant Lisp environment is found.
See section V.6 Executing Lisp Expressions.
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