NAME

Emacs::Run - utilities to assist in using emacs from perl via the shell

SYNOPSIS

use Emacs::Run;
my $er = Emacs::Run->new();
my $major_version = $er->emacs_version;
if ($major_version > 22) {
   print "You have a recent version of emacs\n";
}

# quickly specify additional elisp libraries to use, then get information about emacs settings
my $er = Emacs::Run->new({
                      emacs_libs => [ '~/lib/my-elisp.el', '/usr/lib/site-emacs/stuff.el' ],
                       });
my $emacs_load_path_aref = $er->get_load_path;
my $email = $er->get_variable(  'user-mail-address' );
my $name  = $er->eval_function( 'user-full-name'    );


# suppress the use of the usual emacs init (e.g. ~/.emacs)
my $er = Emacs::Run->new({
                    load_emacs_init => 0,
                 });
my $result = $er->eval_elisp( '(print (+ 2 2))' );  # "4", in case you were wondering


# Specify in detail which emacs lisp libraries should be loaded
$lib_data = [
    [ 'dired',                 { type=>'lib',  priority=>'needed'    } ],
    [ '/tmp/my-load-path.el',  { type=>'file', priority=>'requested' } ],
    [ '/tmp/my-elisp.el',      { type=>'file', priority=>'needed'    } ],
  ];
my $er = Emacs::Run->new({
                    lib_data => $lib_data,
                 });
my $result = $er->eval_lisp( qq{ (print (my-elisp-run-my-code "$perl_string")) } );

DESCRIPTION

Emacs::Run is a module that provides utilities to work with emacs when run from perl as an external process.

The emacs "editor" has some command-line options ("--batch" and so on) that allow you to use it as a lisp interpreter and run elisp code non-interactively.

This module provides methods that use these features of emacs for two types of tasks:

• Probe your emacs installation to get the installed version, the user's current load-path, and so on.

• Run chunks of emacs lisp code without worrying too much about the details of quoting issues and loading libraries and so on.

METHODS

new

Creates a new Emacs::Run object.

Takes a hashref as an argument, with named fields identical to the names of the object attributes. These attributes are:

emacs_path

By default, this code looks for an external program called 'emacs' in a location listed in the shell's PATH environment variable. If you have multiple emacsen installed in different places and/or under different names, you can choose which one will be used by setting this attribute.

shell_output_director

The shell_output_director (sometimes called sod for short) is a string appended to all of the internally generated emacs invocation commands to control what happens to output. This is object attribute is the value used by the elisp evaluation methods documented below, unless another value is specified.

Most methods here accept a hash reference of options that can include their own shell_output_director setting.

Typical values are:

'2>&1'

Intermix STDOUT and STDERR (in elisp: both "message" and "print" functions work). This is the default setting for this object attribute.

'2>/dev/null'

return only STDOUT, throwing away STDERR (in elisp: get output only from "print")

"> $file 2>&1"

send all output to the file $file

">> $file 2>&1"

append all output to the file $file, preserving any existing content.

"2 > $log_file"

return only STDOUT, but save STDERR to $log_file

before_hook

A string inserted into the built-up emacs commands immediately after "--batch", but before any thing else is executed. This is a good place to insert additional invocation options such as "--multibyte" or "--unibyte".

load_emacs_init

Defaults to 1, if set to a false value, will suppress the use of the user's emacs init file (e.g. "~/.emacs").

load_site_init

Defaults to 1, if set to a false value, will suppress the use of the system "site-start.el" file (which loads before the user's init file).

load_default_init

Defaults to 1, if set to a false value, will suppress the use of the system "default.el" file (which loads after the user's init file).

load_no_inits

A convenience flag, used to disable all three types of emacs init files in one step when set to a true value. Overrides the other three.

emacs_libs

A list of emacs libraries (with or without paths) to be loaded automatically. This is provided as a convenience for quick use. To take full control over how your emacs libraries are handled, see "lib_data".

default_priority

The global default for how all the emacs libraries should be loaded. Normally this is set to "requested", but it can be set to "needed".

A 'requested' library will be silently skipped if it is not available (and any elisp code using it may need to do something like 'featurep' checks to adapt to it's absence). A 'needed' file will cause an error to occur if it is not available. Note: this error does not occur during object instantiation, but only after a method is called that needs to load the libraries (e.g. "eval_function" "get_variable", "eval_elisp", "run_elisp_on_file", etc).

lib_data

This is a more complicated data structure than "emacs_libs" which is the preferred interface to use for most uses. Essentially, lib_data is the internal representation that </emacs_libs> is converted into, but the client programmer is provided access to it to cover any unusual needs.

The structure of lib_data is an array of arrays of two elements each, the first element is the library name (a string, with or without path), the second element is a hash of library attributes: 'priority' which can be 'requested' or 'needed' and 'type' which can be 'file' or 'lib'.

Example:

$lib_data = [
  [ 'dired',                 { type=>'lib',  priority=>'needed'    } ],
  [ '/tmp/my-load-path.el',  { type=>'file', priority=>'requested' } ],
  [ '/tmp/my-elisp.el',      { type=>'file', priority=>'needed'    } ],
];

emacs library attributes:

priority

A 'requested' library will be silently skipped if it is not available, but a 'needed' file will cause an error to occur if it is not available. The default priority is 'requested', but that can be changed via the "default_priority" attribute. See "default_priority" for more details.

type

A library of type 'file' should be a filesystem path to a file containing a library of emacs lisp code. A library of type 'lib' is specified by just the basename of the file (sans path or extension), and we will search for it looking in the places specified in the emacs variable load-path. When neither is specified, this module guesses the lib is a file if it looks that way (i.e it has a path and/or extension).

If both lib_data and emacs_libs are used, the lib_data libraries are loaded first, followed by the emacs_libs libraries.

These attributes are used to supply data to the client programmer (i.e. they're intended to be regarded as read-only):

emacs_version

The version number of emacs in use: this is set automatically by the "probe_emacs_version" method during object initialization.

emacs_type

The flavor of emacs in use, e.g. 'Gnu Emacs'. Set automatically by the "probe_emacs_version" method during object initialization.

There are also a number of object attributes intended largely for internal use. The client programmer has access to these, but is not expected to need it. These are documented in "internal attributes".

init

Method that initializes object attributes and then locks them down to prevent accidental creation of new ones.

Any class that inherits from this one should have an "init" of it's own that calls this "init".

get_load_path

Returns the load-path from emacs (by default, using the user's .emacs, if it can be found) as a reference to a perl array.

Changing the $HOME environment variable before running this method results in loading the .emacs file located in the new $HOME.

Uses the object's "shell_output_director" by default, but an overide value can be specified in an options hash reference.

get_variable

Given the name of an emacs variable, returns the value from emacs (when started with the the .emacs located in $HOME, if one is found),

Internally, this uses the emacs 'print' function, which can handle variables containing complex data types, but the return value will be a "printed representation" that may make more sense to emacs than to perl code. For example, the "load-path" variable might look like:

("/home/grunt/lib" "/usr/lib/emacs/site-lisp" "/home/xtra/lib")

By default the returned output includes just STDOUT and not STDERR (and the object attribute "shell_output_director" is ignored), but this behavior can be overridden by setting a field named shell_output_director in the options hashref.

An example of that usage:

my $returned_string =
  $er->get_variable( 'user-mail-address', {
                                            shell_output_director => '2>&1',
                                          } );

eval_function

Given the name of an emacs function, this runs the function (without arguments) and returns the value from emacs (when started with the the .emacs located in $HOME, if one is found).

As with "get_variable", this uses the emacs 'print' function internally.

By default the returned output includes just STDOUT and not STDERR (and the object attribute "shell_output_director" is ignored), but this behavior can be overridden by setting a field named shell_output_director in the options hashref.

TODO at present, the given function is evaluated without arguments. A future version may allow the use of an optional array reference of scalar arguments...

running elisp

These are a set of general methods that run pieces of emacs lisp code in different ways.

The detailed behavior of these methods have a number of things in common:

By default the method first loads the user's initialization file ("$HOME/.emacs") if it can be found. It will also try to load the libraries listed in the "emacs_libs" and/or "lib_data" attributes.

There are object attribute settings that can be used to suppress loading any of the various init files. See "new" for the full list. In particular, if the "load_emacs_init" attribute has been turned off, it will not try to load the .emacs file.

Unless specified otherwise, the methods return the output from the elisp code with STDOUT and STDERR mixed together, though this can be overridden with the shell_output_director field of an options hashref. (The advanatage of intermixing STDOUT and STDERR is that the emacs functions 'message' and 'print' both work to generate output. The disadvantage is that you may have inane messages from emacs sent to STDERR such as 'Loading library so-and-so'.

eval_elisp

Given a string containing a chunk of elisp code this method runs it by invoking emacs in batch mode.

Example:

my $result = $er->eval_elisp( '(print (+ 2 2))' );

eval_elisp_skip_err

Similar to "eval_elisp", except that it always returns only the standard output, ignoring any messages sent to STDERR.

This is essentially for backwards compatibility, though it might be useful as a convenience method to avoid sodding about with the "shell_output_director".

run_elisp_on_file

Given a file name, and some emacs lisp code (which presumably modifies the current buffer), this method opens the file, runs the code on it, and then saves the file.

Returns whatever value the elisp returns.

Example usage: $self->run_elisp_on_file( $filename, $elisp );

internal methods

The following methods are intended primarily for internal use.

Note: the common "leading underscore" naming convention is not used here.

utility methods

quote_elisp

Routine to quote elisp code before feeding it into an emacs batch shell command. Used internally by methods such as "eval_elisp".

This just adds a single backslash to all the double-quote characters (essentially an empirically determined algorithm, i.e. hack).

Example usage:

$elisp = $self->quote_elisp( $elisp );
$emacs_cmd = qq{ emacs --batch --eval "$elisp" 2>&1 };
my $return = qx{ $emacs_cmd };

qx_clean

Executes the given emacs shell invocation string, and returns a cleaned up version of it's returned value. This is intended to be used with elisp that uses the 'print' function, which has spurious leading and trailing newlines and double-quotes.

clean_return_value

Cleans up a given string, trimming unwanted leading and trailing blanks and double quotes.

This is intended to be used with elisp that uses the 'print' function.

initialization phase methods

The following routines are largely used internally in the object initialization phase.

process_emacs_libs_addition

Goes through the given list of emacs_libs, and converts the names into the lib_data style of data structure, appending it to lib_data.

Note that this method works on the given argument, without reference to the object's "emacs_libs" field.

Returns a reference to a structure containing the new additions to lib_data.

process_emacs_libs_reset

This converts the list of emacs_libs into the lib_data style of structure much like "process_emacs_libs_addition", but this method resets the lib_data field to the given value at init time (if any) before appending the new data.

Defaults to using the object's "emacs_libs" setting.

Returns a reference to a structure containing the additions to lib_data from emacs_libs.

set_up_ec_lib_loader

Initializes the ec_lib_loader attribute by scanning for the appropriate emacs init file(s) and processing the list(s) of emacs libraries specified in the object data.

Returns the newly defined $ec_lib_loader string.

This routine is called by "init" during object initialization.

guess_type_from_name

Given the name of an emacs library, examine it to see if it looks like a file system path, or an emacs feature name (sans path or extension)

generation of emacs command strings to load libraries

These are routines that generate a string that can be included in an emacs command line invocation to load certain libraries.

Note the naming convention: "generate emacs command-line" => "genec_".

genec_load_emacs_init

Generates an emacs command line fragment to load the emacs_init file(s) as appropriate.

Side effect: zeroes out the ec_lib_loader before rebuilding with inits only.

The following is a set of four routines to generate a string that can be included in an emacs command line invocation to load the given library. The methods here are named according to the pattern:

"genec_loader_$type_$priority"

All of these methods return the generated string, but also append it to the "ec_lib_loader" attribute,

genec_loader_lib_needed

genec_loader_file_needed

genec_loader_lib_requested

genec_loader_file_requested

Emacs probes

Methods that return information about the emacs installation.

probe_emacs_version

Returns the version of the emacs program stored on your system. This is called during the object initialization phase.

It checks the emacs specified in the object's emacs_path (which defaults to the simple command "emacs", sans any path), and returns the version.

As a side-effect, it sets a number of object attributes with details about the emacs version:

emacs_version
emacs_major_version
emacs_type

parse_emacs_version_string

The emacs version string returned from running "emacs --version" is parsed by this routine, which picks out the version numbers and so on and saves them as object data.

See probe_emacs_version (which uses this internally).

internal utilities (used by initialization code)

elisp_to_load_file

Given the location of an emacs lisp file, generate the elisp that ensures the library will be available and loaded.

find_dot_emacs

Looks for one of the variants of the user's emacs init file (e.g. "~/.emacs") in the same order that emacs would, and returns the first one found.

Note: this relies on the environment variable $HOME. (This can be changed first to cause this to look for an emacs init in some arbitrary location, e.g. for testing purposes.)

This code does not issue a warning if the elc is stale compared to the el, that's left up to emacs.

detect_site_init

Looks for the "site-start.el" file in the raw load-path without loading the regular emacs init file (e.g. ~/.emacs).

Emacs itself normally loads this file before it loads anything else, so this method replicates that behavior.

Returns the library name ('site-start') if found, undef if not.

detect_lib

Looks for the given elisp library in the load-path after trying to load the given list of context_libs (that includes .emacs as appropriate, and this method uses the requested_load_files as context, as well).

Returns $lib if found, undef if not.

Example usage:

if ( $self->detect_lib("dired") ) {
    print "As expected, dired.el is installed.";
}

my @good_libs = grep { defined($_) } map{ $self->detect_lib($_) } @candidate_libs;

routines in use by Emacs::Run::ExtractDocs

elisp_file_from_library_name_if_in_loadpath

Identifies the file associated with a given elisp library name by shelling out to emacs in batch mode.

generate_elisp_to_load_library

Generates elisp code that will instruct emacs to load the given library. It also makes sure it's location is in the load-path, which is not precisely the same thing: See "loaded vs. in load-path".

Takes one argument, which can either be the name of the library, or the name of the file, as distinguished by the presence of a ".el" extension on a file name. Also, the file name will usually have a path included, but the library name can not.

basic setters and getters

The naming convention in use here is that setters begin with "set_", but getters have *no* prefix: the most commonly used case deserves the simplest syntax (and mutators are deprecated).

These accessors exist for all of the object attributes (documented above) irrespective of whether they're expected to be externally useful.

special accessors

append_to_ec_lib_loader

Non-standard setter that appends the given string to the the "elisp_to_load_file" attribute.

append_to_before_hook

Non-standard setter that appends the given string to the the "before_hook" attribute.

Under some circumstances, the code here uses the "before_hook" (for -Q and --no-splash), so using a setter is mildly dangerous. Typically it's better to just append to the "before_hook".

accessors that effect the "ec_lib_loader" attribute

If either lib_data or emacs_libs is modified, this must trigger another run of "set_up_ec_lib_loader" to keep the "ec_lib_loader" string up-to-date.

set_lib_data

Setter for lib_data.

reset_lib_data

Reverts lib_data to the value supplied during initization (it empties it entirely, if none was supplied).

Note: this does not (at present) trigger a re-build of "ec_lib_loader", because it's presumed that this will be triggered by some step following this one.

set_emacs_libs

Setter for emacs_libs.

Side effect: runs process_emacs_libs_rest on the given emacs_libs list.

process_emacs_libs_reset indirectly calls set_up_ec_lib_loader so we don't need to do so explicitly here.

push_emacs_libs

Pushes a new lib to the emacs_libs array.

Takes a string, returns aref of the full list of emacs_libs.

Side-effect: runs process_emacs_libs_addition on the new lib, (appending the new info to lib_data).

process_emacs_libs_addition indirectly calls set_up_ec_lib_loader so we don't need to do so explicitly here.

automatic generation of standard accessors

AUTOLOAD

MOTIVATION

Periodically, I find myself interested in the strange world of running emacs code from perl. There's a mildly obscure feature of emacs command line invocations called "--batch" that essentially transforms emacs into an unusual lisp interpreter: other command-line options allow one to load files of elisp code and run pieces of code from the command-line.

You might think that there aren't many uses for this trick, but I've found several of them. You can use it to:

to probe your emacs set-up from perl, e.g. for automated installation of elisp using perl tools

to test elisp code using a perl test harness.

to use tools written in elisp that you don't want to rewrite in perl (e.g. extract-docstrings.el)

This emacs command line invocation is a little language all of it's own, with just enough twists and turns to it that I've felt the need to write perl routines to help drive the process.

emacs invocation vs Emacs::Run

By default an "emacs --batch" run suppresses most of the usual init files (but does load the essentially deprecated "site-start.pl", presumably for backwards compatibility). Emacs::Run has the opposite bias: here we try to load all three of the types of init files, if they're available, though each one of these can be shut-off individually if so desired. This is because one of the main intended uses is to let perl find out about things such as the user's emacs settings (notably, the load-path). And in any case, the performance hit of loading these files is no-longer such a big deal.

internal documentation (how the code works, etc).

internal attributes

Object attributes intended largely for internal use. The client programmer has access to these, but is not expected to need it. Note: the common "leading underscore" naming convention is not used here.

ec_lib_loader

A fragment of an emacs command line invocation to load emacs libraries. Different attributes exist to specify emacs libraries to be loaded: as these are processed, the ec_lib_loader string gradually accumulates code needed to load them (so that when need be, the process can use the intermediate value of the ec_lib_loader to get the benefit of the previously processed library specifications).

The primary reason for this approach is that each library loaded has the potential to modify the emacs load-path, which may be key for the success of later load attempts.

The process of probing for each library in one of the "requested" lists has to be done in the context of all libraries that have been previously found. Without some place to store intermediate results in some form, this process might need to be programmed as one large monolithic routine.

lib_data_initial

The initial setting of "lib_data" when the object is instantiated. As currently implemented, some operations here require resetting the state of "lib_data" and re-building it. This attribute facilitates that process.

strategies in shelling out

Perl has a good feature for running a shell command and capturing the output: qx{} (aka back-quotes), and it's easy enough to append "2>&1" to a shell command when you'd like to see the STDERR messages intermixed with the STDOUT. This module's methods typically default to capturing all output like this and returning STDOUT and STDERR intermixed like this (though it's perhaps unfortunate that there is no good way to distinguishing between the messages from STDERR and STDOUT later)

From the elisp side, it's important to know that in "--batch" mode, the elisp function message sends output to STDERR, and you need to use the elisp function print if you'd like to send output to STDOUT. Perhaps unfortunately, the print function also brackets all output with double-quotes and newlines -- the Emacs::Run module compensates by unceremoniously stripping these things using the L/<clean_return_value> routine.

Note: the reasoning behind intermixing by default is that this batch-mode behavior of message and print is slightly obscure, even to an elisp programmer: returning everything by default is more likely to result in code that Just Works.

A new feature with the 0.3 release is the "shell_output_director" attribute (plus the addition of a method-specific options to override that object-wide suggested default). This provides the user with finer-grained control over how output is handled.

loaded vs. in load-path

The emacs variable "load-path" behaves much like the shell's $PATH (or perl's @INC): if you try to load a library called "dired", emacs searches through the load-path in sequence, looking for an appropriately named file (e.g. "dired.el"), it then evaluates it's contents, and the objects defined in the file become available for use. It is also possible to load a file by telling emacs the path and filename, and that works whether or not it is located in the load-path.

There is at least a slight difference between the two, however. For example, the present version of the "extract-docstrings.el" library (see Emacs::Run::ExtractDocs) contains code like this, that will break if it is not in the load-path:

(setq codefile (locate-library library))

So some of the routines here (notably "elisp_to_load_file") generate elisp with an extra feature that adds the location of the file to the load-path as well as just loading it.

interactive vs. non-interactive elisp init

Emacs::Run tries to use the user's normal emacs init process even though it runs non-interactively. Unfortunately, it's possible that the init files may need to be cleaned up in order to be used non-interactively. In my case I found that I needed to check the "x-no-window-manager" variable and selectively disable some code that sets X fonts for me:

;; We must do this check to allow "emacs --batch -l .emacs" to work
(unless (eq x-no-window-manager nil)
  (zoom-set-font "-Misc-Fixed-Bold-R-Normal--15-140-75-75-C-90-ISO8859-1"))

TODO

• The method "eval_function" should really pass through any arguments to the function.

• Eliminate unixisms, if possible. A known one: there's a heuristic that spots file paths by looking for "/". Use File::Spec.

• Modify the eval_function method to allow for arguments to be passed through to the function.

• I suspect some quoting issues still lurk e.g. a library filename containing a double-quote will probably crash things.

• Add a method to match an emacs regexp against a string. See: http://obsidianrook.com/devnotes/talks/test_everything/bin/1-test_emacs_regexps.t.html

  (goto-char (point-min))
  (re-search-forward "$elisp_pattern")
  (setq first_capture (match-string 1))

• In "run_elisp_on_file", add support for skipping to a line number after opening a file

SEE ALSO

Emacs::Run::ExtractDocs

Emacs Documentation: Command Line Arguments for Emacs Invocation http://www.gnu.org/software/emacs/manual/html_node/emacs/Emacs-Invocation.html

A lightning talk about (among other things) using perl to test emacs code: "Using perl to test non-perl code":

http://obsidianrook.com/devnotes/talks/test_everything/index.html

AUTHOR

Joseph Brenner, <doom@kzsu.stanford.edu>, 07 Mar 2008

COPYRIGHT AND LICENSE

Copyright (C) 2008 by Joseph Brenner

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.2 or, at your option, any later version of Perl 5 you may have available.

BUGS & LIMITATIONS

When the client coder specifies that a library is "needed", failure occurs relatively late if it's not available: it does not happen during object instantiation, but waits until an attempted run with the object (e.g. "$er->eval_elisp").

cpanm Emacs::Run

perl -MCPAN -e shell
install Emacs::Run