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#### 38.1.4 Command-Line Arguments

You can use command-line arguments to request various actions when you start Emacs. Note that the recommended way of using Emacs is to start it just once, after logging in, and then do all editing in the same Emacs session (see Entering Emacs in The GNU Emacs Manual). For this reason, you might not use command-line arguments very often; nonetheless, they can be useful when invoking Emacs from session scripts or debugging Emacs. This section describes how Emacs processes command-line arguments.

Function: command-line

  This function parses the command line that Emacs was called with, processes it, and (amongst other things) loads the user’s init file and displays the startup messages.

Variable: command-line-processed

  The value of this variable is `t` once the command line has been processed.

  If you redump Emacs by calling `dump-emacs` (see Building Emacs), you may wish to set this variable to `nil` first in order to cause the new dumped Emacs to process its new command-line arguments.

Variable: command-switch-alist

  This variable is an alist of user-defined command-line options and associated handler functions. By default it is empty, but you can add elements if you wish.

  A command-line option is an argument on the command line, which has the form:

      -option

  The elements of the `command-switch-alist` look like this:

      (option . handler-function)

  The CAR, option, is a string, the name of a command-line option (not including the initial hyphen). The handler-function is called to handle option, and receives the option name as its sole argument.

  In some cases, the option is followed in the command line by an argument. In these cases, the handler-function can find all the remaining command-line arguments in the variable `command-line-args-left` (see below). (The entire list of command-line arguments is in `command-line-args`.)

  The command-line arguments are parsed by the `command-line-1` function in the `startup.el` file. See also Command Line Arguments for Emacs Invocation in The GNU Emacs Manual.

Variable: command-line-args

  The value of this variable is the list of command-line arguments passed to Emacs.

Variable: command-line-args-left

  The value of this variable is the list of command-line arguments that have not yet been processed.

Variable: command-line-functions

  This variable’s value is a list of functions for handling an unrecognized command-line argument. Each time the next argument to be processed has no special meaning, the functions in this list are called, in order of appearance, until one of them returns a non-`nil` value.

  These functions are called with no arguments. They can access the command-line argument under consideration through the variable `argi`, which is bound temporarily at this point. The remaining arguments (not including the current one) are in the variable `command-line-args-left`.

  When a function recognizes and processes the argument in `argi`, it should return a non-`nil` value to say it has dealt with that argument. If it has also dealt with some of the following arguments, it can indicate that by deleting them from `command-line-args-left`.

  If all of these functions return `nil`, then the argument is treated as a file name to visit.

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