40.3 Operating System Environment

Emacs provides access to variables in the operating system environment through various functions. These variables include the name of the system, the user's UID, and so on.

Variable: system-configuration

This variable holds the GNU configuration name for the hardware/software configuration of your system, as a string. The convenient way to test parts of this string is with string-match.

Variable: system-type

The value of this variable is a symbol indicating the type of operating system Emacs is operating on. Here is a table of the possible values:

alpha-vms

VMS on the Alpha.

aix-v3

AIX.

berkeley-unix

Berkeley BSD.

dgux

Data General DGUX operating system.

gnu

the GNU system (using the GNU kernel, which consists of the HURD and Mach).

gnu/linux

A GNU/Linux system--that is, a variant GNU system, using the Linux kernel. (These systems are the ones people often call "Linux," but actually Linux is just the kernel, not the whole system.)

hpux

Hewlett-Packard HPUX operating system.

irix

Silicon Graphics Irix system.

ms-dos

Microsoft MS-DOS "operating system." Emacs compiled with DJGPP for MS-DOS binds system-type to ms-dos even when you run it on MS-Windows.

next-mach

NeXT Mach-based system.

rtu

Masscomp RTU, UCB universe.

unisoft-unix

UniSoft UniPlus.

usg-unix-v

AT&T System V.

vax-vms

VAX VMS.

windows-nt

Microsoft windows NT. The same executable supports Windows 9X, but the value of system-type is windows-nt in either case.

xenix

SCO Xenix 386.

We do not wish to add new symbols to make finer distinctions unless it is absolutely necessary! In fact, we hope to eliminate some of these alternatives in the future. We recommend using system-configuration to distinguish between different operating systems.

Function: system-name

This function returns the name of the machine you are running on.

(system-name) => "www.gnu.org"

The symbol system-name is a variable as well as a function. In fact, the function returns whatever value the variable system-name currently holds. Thus, you can set the variable system-name in case Emacs is confused about the name of your system. The variable is also useful for constructing frame titles (see section 29.4 Frame Titles).

Variable: mail-host-address

If this variable is non-nil, it is used instead of system-name for purposes of generating email addresses. For example, it is used when constructing the default value of user-mail-address. See section 40.4 User Identification. (Since this is done when Emacs starts up, the value actually used is the one saved when Emacs was dumped. See section E.1 Building Emacs.)

Command: getenv var

This function returns the value of the environment variable var, as a string. Within Emacs, the environment variable values are kept in the Lisp variable process-environment.

(getenv "USER") => "lewis" lewis@slug[10] % printenv PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin USER=lewis TERM=ibmapa16 SHELL=/bin/csh HOME=/user/lewis

Command: setenv variable value

This command sets the value of the environment variable named variable to value. Both arguments should be strings. This function works by modifying process-environment; binding that variable with let is also reasonable practice.

Variable: process-environment

This variable is a list of strings, each describing one environment variable. The functions getenv and setenv work by means of this variable.

process-environment => ("l=/usr/stanford/lib/gnuemacs/lisp" "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin" "USER=lewis" "TERM=ibmapa16" "SHELL=/bin/csh" "HOME=/user/lewis")

Variable: path-separator

This variable holds a string which says which character separates directories in a search path (as found in an environment variable). Its value is ":" for Unix and GNU systems, and ";" for MS-DOS and MS-Windows.

Function: parse-colon-path path

This function takes a search path string such as would be the value of the PATH environment variable, and splits it at the separators, returning a list of directory names. nil in this list stands for "use the current directory." Although the function's name says "colon," it actually uses the value of path-separator.

(parse-colon-path ":/foo:/bar") => (nil "/foo/" "/bar/")

Variable: invocation-name

This variable holds the program name under which Emacs was invoked. The value is a string, and does not include a directory name.

Variable: invocation-directory

This variable holds the directory from which the Emacs executable was invoked, or perhaps nil if that directory cannot be determined.

Variable: installation-directory

If non-nil, this is a directory within which to look for the `lib-src' and `etc' subdirectories. This is non-nil when Emacs can't find those directories in their standard installed locations, but can find them in a directory related somehow to the one containing the Emacs executable.

Function: load-average &optional use-float

This function returns the current 1-minute, 5-minute, and 15-minute load averages, in a list.

By default, the values are integers that are 100 times the system load averages, which indicate the average number of processes trying to run. If use-float is non-nil, then they are returned as floating point numbers and without multiplying by 100.

(load-average) => (169 48 36) (load-average t) => (1.69 0.48 0.36) lewis@rocky[5] % uptime 11:55am up 1 day, 19:37, 3 users, load average: 1.69, 0.48, 0.36

Function: emacs-pid

This function returns the process ID of the Emacs process.

Variable: tty-erase-char

This variable holds the erase character that was selected in the system's terminal driver, before Emacs was started.

Function: setprv privilege-name &optional setp getprv

This function sets or resets a VMS privilege. (It does not exist on other systems.) The first argument is the privilege name, as a string. The second argument, setp, is t or nil, indicating whether the privilege is to be turned on or off. Its default is nil. The function returns t if successful, nil otherwise.

If the third argument, getprv, is non-nil, setprv does not change the privilege, but returns t or nil indicating whether the privilege is currently enabled.