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screen demands the most out of your terminal so that it can
perform its VT100 emulation most efficiently. These functions provide
means for tweaking the termcap entries for both your physical terminal
and the one simulated by
screentries to emulate as much of the VT100/ANSI standard as possible. But if your terminal lacks certain capabilities the emulation may not be complete. In these cases
screenhas to tell the applications that some of the features are missing. This is no problem on machines using termcap, because
screencan use the
$TERMCAPvariable to customize the standard screen termcap.
But if you do a rlogin on another machine or your machine supports only
terminfo this method fails. Because of this
screen offers a way
to deal with these cases. Here is how it works:
screen tries to figure out a terminal name for itself, it
first looks for an entry named `screen.term', where
term is the contents of your
$TERM variable. If no such entry
screen tries `screen' (or `screen-w', if the
terminal is wide (132 cols or more)). If even this entry cannot be
found, `vt100' is used as a substitute.
The idea is that if you have a terminal which doesn't support an
important feature (e.g. delete char or clear to EOS) you can build a new
termcap/terminfo entry for
`screen.dumbterm') in which this capability has been
disabled. If this entry is installed on your machines you are able to
do a rlogin and still keep the correct termcap/terminfo entry. The
terminal name is put in the
$TERM variable of all new windows.
screen also sets the
$TERMCAP variable reflecting the
capabilities of the virtual terminal emulated.
Furthermore, the variable
$WINDOW is set to the window number of each
The actual set of capabilities supported by the virtual terminal depends
on the capabilities supported by the physical terminal. If, for
instance, the physical terminal does not support underscore mode,
screen does not put the `us' and `ue' capabilities into
$TERMCAP variable, accordingly. However, a minimum number
of capabilities must be supported by a terminal in order to run
screen; namely scrolling, clear screen, and direct cursor
addressing (in addition,
screen does not run on hardcopy
terminals or on terminals that over-strike).
Also, you can customize the
$TERMCAP value used by
termcap command, or by defining the variable
$SCREENCAP prior to startup. When the latter defined, its value will be
copied verbatim into each window's
$TERMCAP variable. This can either
be the full terminal definition, or a filename where the terminal
`screen' (and/or `screen-w') is defined.
screen honors the
terminfo command if the system
uses the terminfo database rather than termcap. On such machines the
$TERMCAP variable has no effect and you must use the
dumptermcap command (see section Write out the window's termcap entry) and the
program to generate terminfo entries for
When the boolean `G0' capability is present in the termcap entry
for the terminal on which
screen has been called, the terminal
screen supports multiple character sets. This
allows an application to make use of, for instance, the VT100 graphics
character set or national character sets. The following control
functions from ISO 2022 are supported: `lock shift G0' (`SI'),
`lock shift G1' (`SO'), `lock shift G2', `lock shift
G3', `single shift G2', and `single shift G3'. When a virtual
terminal is created or reset, the ASCII character set is designated as
`G0' through `G3'. When the `G0' capability is present,
screen evaluates the capabilities `S0', `E0', and `C0' if
present. `S0' is the sequence the terminal uses to enable and start
the graphics character set rather than `SI'. `E0' is the
corresponding replacement for `SO'. `C0' gives a character by
character translation string that is used during semi-graphics mode.
This string is built like the `acsc' terminfo capability.
When the `po' and `pf' capabilities are present in the
terminal's termcap entry, applications running in a
can send output to the printer port of the terminal. This allows a user
to have an application in one window sending output to a printer
connected to the terminal, while all other windows are still active (the
printer port is enabled and disabled again for each chunk of output).
As a side-effect, programs running in different windows can send output
to the printer simultaneously. Data sent to the printer is not
displayed in the window.
Some capabilities are only put into the
$TERMCAP variable of the virtual
terminal if they can be efficiently implemented by the physical
terminal. For instance, `dl' (delete line) is only put into the
$TERMCAP variable if the terminal supports either delete line itself or
scrolling regions. Note that this may provoke confusion, when the
session is reattached on a different terminal, as the value of
cannot be modified by parent processes. You can force
include all capabilities in
$TERMCAP with the `-a'
command-line option (see section Invoking
Write the termcap entry for the virtual terminal optimized for the currently active window to the file `.termcap' in the user's `$HOME/.screen' directory (or wherever
screen stores its
sockets. see section Files Referenced). This termcap entry is identical to
the value of the environment variable
$TERMCAP that is set up by
screen for each window. For terminfo based systems you will need
to run a converter like
captoinfo and then compile the entry with
Command: terminfo term terminal-tweaks [window-tweaks]
Use this command to modify your terminal's termcap entry without going through all the hassles involved in creating a custom termcap entry. Plus, you can optionally customize the termcap generated for the windows. If your system uses the terminfo database rather than termcap,
screen will understand the
terminfo command which
has the same effects as the
termcap command. Thus users can write
one .screenrc file that handles both cases, although terminfo syntax is
slightly different from termcap syntax.
The first argument specifies which terminal(s) should be affected by this definition. You can specify multiple terminal names by separating them with `|'s. Use `*' to match all terminals and `vt*' to match all terminals that begin with `vt'.
Each tweak argument contains one or more termcap defines (separated by `:'s) to be inserted at the start of the appropriate termcap entry, enhancing it or overriding existing values. The first tweak modifies your terminal's termcap, and contains definitions that your terminal uses to perform certain functions. Specify a null string to leave this unchanged (e.g. ""). The second (optional) tweak modifies all the window termcaps, and should contain definitions that screen understands (see section Virtual Terminal).
termcap xterm* xn:hs@
screen that all terminals that begin with `xterm'
have firm auto-margins that allow the last position on the screen to be
updated (xn), but they don't really have a status line (no 'hs' --
append `@' to turn entries off). Note that we assume `xn' for
all terminal names that start with `vt', but only if you don't
specify a termcap command for that terminal.
termcap vt* xn termcap vt102|vt220 Z0=\E[?3h:Z1=\E[?3l
Specifies the firm-margined `xn' capability for all terminals that begin with `vt', and the second line will also add the escape-sequences to switch into (Z0) and back out of (Z1) 132-character-per-line mode if this is a VT102 or VT220. (You must specify Z0 and Z1 in your termcap to use the width-changing commands.)
termcap vt100 "" l0=PF1:l1=PF2:l2=PF3:l3=PF4
This leaves your vt100 termcap alone and adds the function key labels to each window's termcap entry.
termcap h19|z19 am@:im=\E@:ei=\EO dc=\E[P
Takes a h19 or z19 termcap and turns off auto-margins (am@) and enables the insert mode (im) and end-insert (ei) capabilities (the `@' in the `im' string is after the `=', so it is part of the string). Having the `im' and `ei' definitions put into your terminal's termcap will cause screen to automatically advertise the character-insert capability in each window's termcap. Each window will also get the delete-character capability (dc) added to its termcap, which screen will translate into a line-update for the terminal (we're pretending it doesn't support character deletion).
If you would like to fully specify each window's termcap entry, you
should instead set the
$SCREENCAP variable prior to running
screen. See section Virtual Terminal, for the details of the
screen terminal emulation. See section `Termcap' in The Termcap Manual, for more information on termcap definitions.
screenand are not in the termcap manual (see section `Termcap' in The Termcap Manual).
screennow uses `xn' instead.
screento look out for characters with 8th bit set. If such a character is found
screenprocesses the specified string and than outputs the character with the 8th bit stripped off. Note that the string can contain any esc-sequences known to
screen, too. (Example: Single Shift G2 = \EN.)
flow off. The opposite of this capability is `nx'.
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