Invoking Guile
==============

Many features of Guile depend on and can be changed by information that the user provides either before or when Guile is started.  Below is a description of what information to provide and how to provide it.

Command-line Options
--------------------

Here we describe Guile's command-line processing in detail.  Guile processes its arguments from left to right, recognizing the switches described below.  For examples, see Scripting Examples.

SCRIPT ARG...
-s SCRIPT ARG...
     By default, Guile will read a file named on the command line as a script.  Any command-line arguments ARG... following SCRIPT become the script's arguments; the command-line function returns a list of strings of the form (SCRIPT ARG...).

     It is possible to name a file using a leading hyphen, for example, -myfile.scm.  In this case, the file name must be preceded by -s to tell Guile that a (script) file is being named.

     Scripts are read and evaluated as Scheme source code just as the load function would.  After loading SCRIPT, Guile exits.

-c EXPR ARG...
     Evaluate EXPR as Scheme code, and then exit.  Any command-line arguments ARG... following EXPR become command-line arguments; the command-line function returns a list of strings of the form (GUILE ARG...), where GUILE is the path of the Guile executable.

-- ARG...
     Run interactively, prompting the user for expressions and evaluating them.  Any command-line arguments ARG... following the -- become command-line arguments for the interactive session; the command-line function returns a list of strings of the form (GUILE ARG...), where GUILE is the path of the Guile executable.

-L DIRECTORY
     Add DIRECTORY to the front of Guile's module load path.  The given directories are searched in the order given on the command line and before any directories in the GUILE_LOAD_PATH environment variable.  Paths added here are not in effect during execution of the user's .guile file.

-C DIRECTORY
     Like -L, but adjusts the load path for compiled files.

-x EXTENSION
     Add EXTENSION to the front of Guile's load extension list (see %load-extensions).  The specified extensions are tried in the order given on the command line, and before the default load extensions.  Extensions added here are not in effect during execution of the user's .guile file.

-l FILE
     Load Scheme source code from FILE, and continue processing the command line.

-e FUNCTION
     Make FUNCTION the entry point of the script.  After loading the script file (with -s) or evaluating the expression (with -c), apply FUNCTION to a list containing the program name and the command-line arguments---the list provided by the command-line function.

     A -e switch can appear anywhere in the argument list, but Guile always invokes the FUNCTION as the last action it performs. This is weird, but because of the way script invocation works under POSIX, the -s option must always come last in the list.

     The FUNCTION is most often a simple symbol that names a function that is defined in the script.  It can also be of the form (@ MODULE-NAME SYMBOL), and in that case, the symbol is looked up in the module named MODULE-NAME.

     For compatibility with some versions of Guile 1.4, you can also use the form (symbol ...) (that is, a list of only symbols that doesn't start with @), which is equivalent to (@ (symbol ...) main), or (symbol ...)  symbol (that is, a list of only symbols followed by a symbol), which is equivalent to (@ (symbol ...) symbol).  We recommend to use the equivalent forms directly since they correspond to the (@ ...)  read syntax that can be used in normal code.  See Using Guile Modules and Scripting Examples.

-ds
     Treat a final -s option as if it occurred at this point in the command line; load the script here.

     This switch is necessary because, although the POSIX script invocation mechanism effectively requires the -s option to appear last, the programmer may well want to run the script before other actions requested on the command line.  For examples, see Scripting Examples.

\
     Read more command-line arguments, starting from the second line of the script file.  See The Meta Switch.

--use-srfi=LIST
     The option --use-srfi expects a comma-separated list of numbers, each representing a SRFI module to be loaded into the interpreter before evaluating a script file or starting the REPL.  Additionally, the feature identifier for the loaded SRFIs is recognized by the procedure cond-expand when this option is used.

     Here is an example that loads the modules SRFI-8 ('receive') and SRFI-13 ('string library') before the GUILE interpreter is started:

          guile --use-srfi=8,13

--debug
     Start with the debugging virtual machine (VM) engine.  Using the debugging VM will enable support for VM hooks, which are needed for tracing, breakpoints, and accurate call counts when profiling.  The debugging VM is slower than the regular VM, though, by about ten percent.  See VM Hooks, for more information.

     By default, the debugging VM engine is only used when entering an interactive session.  When executing a script with -s or -c, the normal, faster VM is used by default.

     1.8

--no-debug
     Do not use the debugging VM engine, even when entering an interactive session.

     Note that, despite the name, Guile running with --no-debug does support the usual debugging facilities, such as printing a detailed backtrace upon error.  The only difference with --debug is lack of support for VM hooks and the facilities that build upon it (see above).

-q
     Do not load the initialization file, .guile.  This option only has an effect when running interactively; running scripts does not load the .guile file.  See Init File.

--listen[=P]
     While this program runs, listen on a local port or a path for REPL clients.  If P starts with a number, it is assumed to be a local port on which to listen.  If it starts with a forward slash, it is assumed to be the file name of a UNIX domain socket on which to listen.

     If P is not given, the default is local port 37146.  If you look at it upside down, it almost spells ``Guile''.  If you have netcat installed, you should be able to nc localhost 37146 and get a Guile prompt.  Alternately you can fire up Emacs and connect to the process; see Using Guile in Emacs for more details.

          Opening a port allows anyone who can connect to that port to do anything Guile can do, as the user that the Guile process is running as.  Do not use --listen on multi-user machines.  Of course, if you do not pass --listen to Guile, no port will be opened.

          Guile protects against the HTTP inter-protocol exploitation attack (https://en.wikipedia.org/wiki/Inter-protocol_exploitation), a scenario whereby an attacker can, via an HTML page, cause a web browser to send data to TCP servers listening on a loopback interface or private network. Nevertheless, you are advised to use UNIX domain sockets, as in --listen=/some/local/file, whenever possible.

     That said, --listen is great for interactive debugging and development.

     2.0

--auto-compile
     Compile source files automatically (default behavior).

     2.0.1

--fresh-auto-compile
     Treat the auto-compilation cache as invalid, forcing recompilation.

     2.0

--no-auto-compile
     Disable automatic source file compilation.

     2.0.8

--language=LANG
     For the remainder of the command line arguments, assume that files mentioned with -l and expressions passed with -c are written in LANG.  LANG must be the name of one of the languages supported by the compiler (see Compiler Tower).  When run interactively, set the REPL's language to LANG (see Using Guile Interactively).

     The default language is scheme; other interesting values include elisp (for Emacs Lisp), and ecmascript.

     The example below shows the evaluation of expressions in Scheme, Emacs Lisp, and ECMAScript:

          guile -c "(apply + '(1 2))"
          guile --language=elisp -c "(= (funcall (symbol-function '+) 1 2) 3)"
          guile --language=ecmascript -c '(function (x) { return x * x; })(2);'

     To load a file written in Scheme and one written in Emacs Lisp, and then start a Scheme REPL, type:

          guile -l foo.scm --language=elisp -l foo.el --language=scheme

     2.0

-h, --help
     Display help on invoking Guile, and then exit.

-v, --version
     Display the current version of Guile, and then exit.

Environment Variables
---------------------

The environment is a feature of the operating system; it consists of a collection of variables with names and values.  Each variable is called an environment variable (or, sometimes, a ``shell variable''); environment variable names are case-sensitive, and it is conventional to use upper-case letters only.  The values are all text strings, even those that are written as numerals.  (Note that here we are referring to names and values that are defined in the operating system shell from which Guile is invoked.  This is not the same as a Scheme environment that is defined within a running instance of Guile. For a description of Scheme environments, see About Environments.)

How to set environment variables before starting Guile depends on the operating system and, especially, the shell that you are using.  For example, here is how to tell Guile to provide detailed warning messages about deprecated features by setting GUILE_WARN_DEPRECATED using Bash:

     $ export GUILE_WARN_DEPRECATED="detailed"
     $ guile

Or, detailed warnings can be turned on for a single invocation using:

     $ env GUILE_WARN_DEPRECATED="detailed" guile

If you wish to retrieve or change the value of the shell environment variables that affect the run-time behavior of Guile from within a running instance of Guile, see Runtime Environment.

Here are the environment variables that affect the run-time behavior of Guile:

GUILE_AUTO_COMPILE
     This is a flag that can be used to tell Guile whether or not to compile Scheme source files automatically.  Starting with Guile 2.0, Scheme source files will be compiled automatically, by default.

     If a compiled (.go) file corresponding to a .scm file is not found or is not newer than the .scm file, the .scm file will be compiled on the fly, and the resulting .go file stored away.  An advisory note will be printed on the console.

     Compiled files will be stored in the directory $XDG_CACHE_HOME/guile/ccache, where XDG_CACHE_HOME defaults to the directory $HOME/.cache.  This directory will be created if it does not already exist.

     Note that this mechanism depends on the timestamp of the .go file being newer than that of the .scm file; if the .scm or .go files are moved after installation, care should be taken to preserve their original timestamps.

     Set GUILE_AUTO_COMPILE to zero (0), to prevent Scheme files from being compiled automatically.  Set this variable to ``fresh'' to tell Guile to compile Scheme files whether they are newer than the compiled files or not.

     See Compilation.

GUILE_HISTORY
     This variable names the file that holds the Guile REPL command history. You can specify a different history file by setting this environment variable.  By default, the history file is $HOME/.guile_history.

GUILE_INSTALL_LOCALE
     This is a flag that can be used to tell Guile whether or not to install the current locale at startup, via a call to (setlocale LC_ALL "") (The GUILE_INSTALL_LOCALE environment variable was ignored in Guile versions prior to 2.0.9.).  See Locales, for more information on locales.

     You may explicitly indicate that you do not want to install the locale by setting GUILE_INSTALL_LOCALE to 0, or explicitly enable it by setting the variable to 1.

     Usually, installing the current locale is the right thing to do.  It allows Guile to correctly parse and print strings with non-ASCII characters.  However, for compatibility with previous Guile 2.0 releases, this option is off by default.  The next stable release series of Guile (the 2.2 series) will install locales by default.

GUILE_STACK_SIZE
     Guile currently has a limited stack size for Scheme computations. Attempting to call too many nested functions will signal an error.  This is good to detect infinite recursion, but sometimes the limit is reached for normal computations.  This environment variable, if set to a positive integer, specifies the number of Scheme value slots to allocate for the stack.

     In the future we will implement stacks that can grow and shrink, but for now this hack will have to do.

GUILE_LOAD_COMPILED_PATH
     This variable may be used to augment the path that is searched for compiled Scheme files (.go files) when loading.  Its value should be a colon-separated list of directories.  If it contains the special path component ... (ellipsis), then the default path is put in place of the ellipsis, otherwise the default path is placed at the end. The result is stored in %load-compiled-path (see Load Paths).

     Here is an example using the Bash shell that adds the current directory, ., and the relative directory ../my-library to %load-compiled-path:

          $ export GUILE_LOAD_COMPILED_PATH=".:../my-library"
          $ guile -c '(display %load-compiled-path) (newline)'
          (. ../my-library /usr/local/lib/guile/2.0/ccache)

GUILE_LOAD_PATH
     This variable may be used to augment the path that is searched for Scheme files when loading.  Its value should be a colon-separated list of directories.  If it contains the special path component ... (ellipsis), then the default path is put in place of the ellipsis, otherwise the default path is placed at the end.  The result is stored in %load-path (see Load Paths).

     Here is an example using the Bash shell that prepends the current directory to %load-path, and adds the relative directory ../srfi to the end:

          $ env GUILE_LOAD_PATH=".:...:../srfi" \
          guile -c '(display %load-path) (newline)'
          (. /usr/local/share/guile/2.0 \
          /usr/local/share/guile/site/2.0 \
          /usr/local/share/guile/site \
          /usr/local/share/guile \
          ../srfi)

     (Note: The line breaks, above, are for documentation purposes only, and not required in the actual example.)

GUILE_WARN_DEPRECATED
     As Guile evolves, some features will be eliminated or replaced by newer features.  To help users migrate their code as this evolution occurs, Guile will issue warning messages about code that uses features that have been marked for eventual elimination.  GUILE_WARN_DEPRECATED can be set to ``no'' to tell Guile not to display these warning messages, or set to ``detailed'' to tell Guile to display more lengthy messages describing the warning.  See Deprecation.

HOME
     Guile uses the environment variable HOME, the name of your home directory, to locate various files, such as .guile or .guile_history.