lfe.txt

lfe(1)                                                                  lfe(1)



NAME
       lfe - Lisp Flavoured Erlang (LFE) shell

SYNOPSIS
       lfe  is a simple LFE repl (read-eval-print loop) in which you can enter
       sexprs which then are evaluated and the value printed.   You  can  also
       define  local  functions  and  macros as well as set variables.  It can
       read commands either from the standard input or from a file.

       The LFE repl is implemented in the module lfe_shell.

BUILT-IN SHELL FUNCTIONS
       These are defined as normal functions and macros and can be called from
       anywhere  in  the shell.  They can even be redefined.  They can also be
       explicitly called (: lfe_shell ...).

       (c File [Options])

       Compile and load an LFE file.  Assumes default extension .lfe.

       (: c Command Arg ...)

       (c:Command Arg ...)

       All the commands in the standard Erlang shell can be  reached  in  this
       way.

       (cd Dir)

       Change the working directory.

       (clear)

       Clear the REPL output.

       (ec File [Options])

       Compile and load an Erlang file.

       (ep Expr [Depth])

       (epp Expr [Depth])

       Print/prettyprint  a value in Erlang form to either the specified depth
       or if no value is given the full depth.

       (flush)

       Flush any messages sent to the shell.

       (h)

       (help)

       Print usage info.

       (h Mod)

       (h Mod Mac)

       (h Mod Fun Arity)

       Print out help information of a module/macro/function.

       (i [(list Pid ...)])

       Print information about a list of pids.  If no list is given then print
       information about currently running processes in the system.

       (i x y z)

       Print information about the about #Pid<x.y.z>

       (l Module ...)

       Load modules.

       (ls)

       (ls dir)

       List files in a directory.  If no directory is given then list files in
       the current directory.

       (m [Module ...])

       Print out module information.  If no modules are given then  print  in‐
       formation about all modules.

       (p Expr [Depth])

       (pp Expr [Depth])

       Print/prettyprint  a value to either the specified depth or if no value
       is given the full depth.

       (pid x y z)

       Create a pid from x, y, z.

       (pwd)

       Print the current working directory.

       (q)

       Quit - shorthand for init:stop/0.

       (regs)

       Print information about the registered processes in the system.

BUILT-IN SHELL COMMANDS
       These are special forms which are only recognised at the  top-level  in
       shell input.  The cannot be redefined.

       (reset-environment)

       Resets the environment to its initial state.  This will clear all vari‐
       ables, functions and macros that have been set.

       (run File)

       Execute all the shell commands in File.  All defined  variables,  func‐
       tions  and  macros will be saved in the environment if there are no er‐
       rors.

       (set Pattern Expr)

       (set Pattern (when Guard) Expr)

       Evaluate Expr and match the result with Pattern  binding  variables  in
       it.   These variables can then be used in the shell and also rebound in
       another set.

       (slurp File)

       Slurp in a source LFE file and makes all functions and  macros  defined
       in  the file available in the shell.  Only one file can be slurped at a
       time and slurping a new file basically does an unslurp first.

       (unslurp)

       Revert back to the state before the last slurp  removing  all  function
       and macro definitions both in the slurped file and defined in the shell
       since then.

SHELL FUNCTIONS AND MACROS
       Functions and macros can be defined in the shell.  These will  only  be
       local  to  the  shell and cannot be called from modules.  The forms are
       the standard forms for defining functions and macros.

       (defun Fun ...)

       Define a function in the shell.

       (defmacro Macro ...)

       Define a macro in the shell.

BUILT-IN SHELL VARIABLES
       +, ++, +++

       The three previous expressions input.

       *, **, ***

       The values of the previous three expressions.

       -

       The current expression input.

SHELL ENVIRONMENT
       The shell maintains an environment of local function and macro  defini‐
       tions,  and  variable  bindings.  The environment can be accessed using
       the built-in shell variable $ENV.  This  can  be  useful  when  calling
       functions  like macroexpand and macro-function which unless an explicit
       environment is given will only search the default environment.

STARTING THE LFE SHELL
       After installing the best way is probably to start Erlang directly run‐
       ning the LFE shell with:

              lfe [flags]

       From  a normal Erlang shell the best way to start the shell is by call‐
       ing:

              17> lfe_shell:server().

       Giving the user switch commands:

              --> s lfe_shell
              --> c

       will create a job running the LFE shell and connect to it.   This  also
       works when starting a remote shell.

       Flags that LFE recognizes include the following:

       · -nobanner - starts LFE without showing the banner

       · -h or --help - provides command line usage help

       · -e or -eval - evaluates a given sexpr in a string

       · -prompt  - users may supply a value here to override the default lfe>
         prompt; note that -prompt classic will set the prompt to the original
         >  and  -prompt  with  no associated value will cause no prompt to be
         displayed at all.  These also work when node names are provided (with
         either -sname or -name).  Furthermore, users may override the default
         formatting of node names in prompts by providing a prompt value  con‐
         taining  the  string ~node (which will be substituted with the actual
         name of the node).

       There can be multiple string expressions to be evaluated; each one must
       be prefixed with an -e or -eval.  String expressions are run in the LFE
       repl so shell commands and functions are allowed.  They are all run  in
       the same invocation of the repl so:

              $ lfe -e "(set aaa 42)" -e "(set bbb 84)" -e "(pp (tuple aaa bbb))"
              #(42 84)

       If there are string expressions then the LFE repl will not be run.

RUNNING LFE SHELL SCRIPTS
       The  LFE  shell  can  also  be directly called to run LFE shell scripts
       with:

              lfe [flags] file [args]

       This will start the shell, run a script with  LFE  shell  commands  and
       then  terminate  the  shell.  The following built-in variables are also
       bound:

       script-name

       The name of the script file as a string.

       script-args

       A list of the arguments to the script as strings.  If no arguments have
       been given then this will be an empty list.

       Note  that  if  there  are  any string expressions to be evaluated then
       these must come before the name of the script file and  its  arguments.
       These  expressions  will  be evaluated before the script and the script
       will use the environment from the string expressions.

       It is possible to run both string expressions and an LFE  shell  script
       and they are then run in the same LFE repl.

SEE ALSO
       lfescript(1), lfe_guide(7) lfe_doc(3)

AUTHORS
       Robert Virding.



                                   2008-2020                            lfe(1)