Setterm is used to build a STREAMS configuration on a tty line. It expects to be called with stdin, stdout, and stderr all attached to a terminal line, though it will usually work if only standard input is connected to a terminal line. It will normally be called with some kind of line discipline already pushed onto the line, since getty needs to push a line discipline that can be used by login.
If invoked with no arguments, setterm looks at the user's environment for a $TERM variable. If none is found, setterm exits, since it needs the $TERM information to do any further processing. If the -t option is given with an argument, the next argument (TERMNAME) is taken to be the name of a terminal type. The terminal name is looked up in the terminfo(4) database and the field "devt" (if one exists) is extracted from the entry. If there is no "devt" field, the terminal is assumed to be ASCII, requiring no additional processing, and setterm will then print the message "Device is ASCII" and exit.
Setterm then runs the commands in its configuration file associated with the "devt" field in the terminfo(4) entry. If the -t option is not given, or if there are no command line arguments, then it is an error for no entry to match. In that case setterm exits with an error message.
If the -x option is given, the following argument (NAME) is taken to be a "devt" field appearing in the configuration file. The terminfo(4) entry is not looked up, but the argument is used instead. The matching entry in the configuration file is executed unconditionally; therefore the -x option should be used with caution. The -x option is most useful for testing modules, and in switching between configurations dynamically, or for overriding the default entry for a particular "devt" type. The following "devt" fields are registered in each locale's configuration file:
Chinese/PRC locale (locale name = "zh")
Chinese/Taiwan locale (locale name = "zh_TW" / "zh_TW.BIG5")
Japanese locale (locale name = "ja")
Japanese locale (locale name = "ja_JP.PCK")
Korean locale (locale name = "ko")
Korean locale (locale name = "ko.UTF-8")
The -v option is used to verify that the contents of the configuration file are correct. It prints debugging output for each entry in the configuration file, but does not perform any of the actions. It is only used for syntactic verification of configurations.
If the "devt" field is present for the given terminal, its value is used in searching the configuration file for an appropriate entry. The line in the configuration file is parsed and the actions carried out by setterm.
If the user's environment contains the variable $SETTLIB, it is taken to be the pathname of a file to use as the configuration file instead of the default configuration file, allowing per-user customization.
For languages requiring dictionary modules or other specialized processing capability the "run" command can be used to send appropriate ioctl(2) commands and do special purpose (i.e. language dependent) processing once the Stream has been built, or appropriate modules pushed. Programs run via the "run" command for this purpose, generally residing in the setterm library, are known as initialization programs.
As distributed, the setterm configuration file comes with a few examples, and the format should be self-explanatory. Lines beginning with "#" (in the first column only) are ignored as comments.
The setterm command language is very simple. Each entry occupies a single logical line in the configuration file. Newlines may be escaped with a backslash so that entries may be spread over several physical lines for ease of editing. Each entry consists of an identifying word (which normally matches a "devt" entry of the terminfo(4) database) and a list of actions. Each action is separated by whitespace (spaces, tabs, or escaped newlines). A "word" is defined as a block of alpha-numeric or special printing characters containing no whitespace or control characters.
An action consists of a command word, which may be followed by a single argument word. The argument word is separated from the command word by either a comma or whitespace.
An argument word must not contain any spaces or tabs, but may have internal delimiters, such as colons and commas.
For example:
Acceptable: A=ldterm:eldterm,ld0:eld0
Unacceptable: A = ldterm: eldterm , ld0:eld0
The following commands are recognized. "NAME", "NAMELIST", "MOD1", and "MOD2", indicate the names of modules; "NAMELIST" indicates one or more of module names separated (with no space) by a vertical bar ("|" symbol); "CMD" indicates a shell command line; "VAR" indicates a single letter variable name from "A" through "F"; "WORDLIST" indicates a special wordlist for the "select" command:
cmd Arguments Action(s)
pop none pop one module
popto NAMELIST pop until it encounters one of
modules in NAMELIST or there is no
more to pop
popall none pop all modules
throw none save termio(7) settings
catch none restore termio(7) settings
push NAME push module name
run { CMD } run command line between {}
set VAR set VAR to name of top module
if VAR=NAME?MOD1:MOD2 if the value of VAR is equal
to NAME, then push MOD1, else
push MOD2
test VAR=NAME set VAR to
NAME if the module "NAME" is in the
STREAM
select VAR=WORDLIST test "VAR" against the left
word of each pair in "WORDLIST";
push the first right word that matches
Some special words are recognized for the "if", "test" and "select" commands. These words are:
END stop processing and exit
NUL do nothing
POP pop a module rather than pushing
ELSE as first of a pair in a WORDLIST,
match any value including a NULL string
The argument to an "if" command, as shown above, has the following meaning: if the value of the given variable matches the literal module name "NAME", then the action "MOD1" is taken, otherwise the action "MOD2" is taken. If no alternate action is desired, the colon and "MOD2" may be elided. The action for a module name is, by default, to push it. If the module name is one of the special names, then the action associated with the special name is taken. An "ELSE" keyword may not appear in a "test" or "if" command. The "END" keyword may not appear as the value to test a variable against, but only as an action to take on a match.
The "WORDLIST" for a "select" command is a variable name, an equal sign, then a list of word pairs of the form "WORD.WORD". Each word pair is separated from the others by a comma. Thus, a whole "select" command might look like:
The "ELSE" keyword cannot, of course be used as the right word of a pair, nor can the "END" keyword be used as the left word of a pair; "NUL" can be either.
The "run" command is exceptional in that its argument may contain spaces between the curly braces. An action for a "run" command might be:
Commands invoked through the "run" command should reside in the directory /usr/share/lib/setterm, though this is not required. They should not require too many arguments as they are intended to be very specialized. In general, they perform any device- or language-dependent processing on behalf of setterm, which has no language-dependent processing capability.
If setterm was invoked with the -t option, then programs invoked through the "run" command will have their environment $TERM variable replaced with the terminal name indicated in the argument to the -t option.
The "throw" command saves the termio(7) settings of the tty. They can be restored (presumably after the line discipline or other module has changed) through the "catch" command. These are useful for switching line disciplines, when both the old and new line disciplines support, as a minimum, the termio(7) interface. If a "catch" is done without a prior "throw", then the command line "stty sane" will be done instead of the "catch" (useful for restoring badly messed up Streams); thus a "catch" with no throw is equivalent to "run{stty sane}". Two "throw" cannot be done without a "catch" between them.
#
# Japanese 7-bit JIS terminal
JapanJIS7|JIS7throw\
popto zs|mcp|mti|ptem\
push jconv7\
push ldterm\
push ttcompat\
catch
#
This entry can be invoked with,
% setterm -x JIS7
As noted, the escaped newlines are necessary since the entry must be
all on a single logical line. Escaped newlines are treated as single
space characters.
The "devt" label in the configuration file may optionally be a list of words separated (with no spaces) by a vertical bar ("|" symbol). In this case, each one is scanned by setterm for a match when looking for an entry in the file; if any word of the "|" separated list matches, that entry is used.
There is an extra variable, "T", which when set with the set command, takes on a generic device name. When this variable is set, a call to ttyname(3) on file descriptor zero is issued by setterm. The resulting device name is stripped of any trailing ASCII digits (i.e., 0-9), and the result becomes the value of the "T" variable. This is useful if specialized processing is necessary for different device types or drivers, for example if the console requires special-purpose processing. Actual device names, such as "/dev/tty33" are turned into names such as "/dev/tty". Beware that names containing no trailing digits cannot be stripped of them, so that "/dev/console" remains just that. An example of usage might be:
Currently, the maximum size of a single "action" entry is limited to 2047 bytes. The number of items in a "select" list is limited to 30. Setterm unfortunately cannot be used to build multiplexing configurations. The "run" command may help where multiplexing configurations are required. Setterm will neither save nor restore termio(7) settings, except through "throw" and "catch".
Error reporting is minimal; all errors are fatal. Inability to pop a module is not an error, since it may signal the "bottom" of the STREAM.
The configuration file is scanned sequentially, and only the first entry found for a particular "devt" is executed.
Since all errors are fatal, the user could be left with an extremely "raw" terminal configuration, or worse, with a completely useless configuration from which there is no escape except by logging out (if any input is possible at all!). "Throw", "catch", and tests for existence of a reasonable top-level module should help reduce these possibilities. Rigorous testing of new entries under varying conditions is recommended. It is also recommended that a "sane" entry of some type be inserted into the configuration file for use with the -x option.
Setterm uses its standard input file (file descriptor zero) for all ioctl(2) calls to the terminal. Therefore, if the terminal should hang (for example if all modules have been popped but it is impossible to push anything, or in the event of a module hangup or failure) it is possible to run setterm from another terminal (assuming appropriate permissions) with standard input redirected to the errant terminal line. For example, if tty12 is hung due to a module problem, "setterm-x ... < /dev/tty12" should clear the problem.
Beware of infinite recursion when calling setterm recursively (i.,e., when "run { setterm ... }" from within an entry; setterm cannot detect infinite recursion.
Documentation on various local modules
A missing "}" to a "run" command may not be caught by the parser, which is relatively crude. This can result in bad arguments to commands, without the syntax error being caught.