THE VIRTUAL TERMINAL Each window in a screen session emulates a VT100 terminal, with some extra functions added. The VT100 emulator is hard-coded, no other terminal types can be emulated. Usually screen tries 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 screen has to tell the applications that some of the features are missing. This is no problem on machines using termcap, because screen can use the $TERMCAP variable 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: When screen tries to figure out a terminal name for itself, it first looks for an entry named "screen.", where is the contents of your $TERM variable. If no such entry exists, 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 sup- port an important feature (e.g. delete char or clear to EOS) you can build a new termcap/terminfo entry for screen (named "screen.") 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 vir- tual terminal emulated. Notice that, however, on machines using the terminfo database this variable has no effect. Furthermore, the variable $WINDOW is set to the window number of each window. 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 the window's $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 screen by using the "termcap" .screenrc command, or by defining the variable $SCREENCAP prior to startup. When the is 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. Note that screen honors the "terminfo" .screenrc command if the system uses the terminfo database rather than term- cap. When the boolean `G0' capability is present in the termcap entry for the terminal on which screen has been called, the terminal emulation of screen supports multiple charac- ter 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 corre- sponding 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' ter- minfo capability. When the `po' and `pf' capabilities are present in the terminal's termcap entry, applications running in a screen window can send output to the printer port of the termi- nal. This allows a user to have an application in one window sending output to a printer connected to the termi- nal, while all other windows are still active (the printer port is enabled and disabled again for each chunk of out- put). 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. The info command displays a line starting `PRIN' while the printer is active. Screen maintains a hardstatus line for every window. If a window gets selected, the display's hardstatus will be updated to match the window's hardstatus line. If the dis- play has no hardstatus the line will be displayed as a standard screen message. The hardstatus line can be changed with the ANSI Application Program Command (APC): "ESC_ESC\". As a convenience for xterm users the sequence "ESC]0..2;^G" is also accepted. Some capabilities are only put into the $TERMCAP variable of the virtual terminal if they can be efficiently imple- mented 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 $TERMCAP cannot be modified by parent pro- cesses. The following is a list of control sequences recognized by screen. "(V)" and "(A)" indicate VT100-specific and ANSI- or ISO-specific functions, respectively. ESC E Next Line ESC D Index ESC M Reverse Index ESC H Horizontal Tab Set ESC Z Send VT100 Identification String ESC 7 (V) Save Cursor and Attributes ESC 8 (V) Restore Cursor and Attributes ESC [s (A) Save Cursor and Attributes ESC [u (A) Restore Cursor and Attributes ESC c Reset to Initial State ESC g Visual Bell ESC Pn p Cursor Visibility (97801) Pn = 6 Invisible 7 Visible ESC = (V) Application Keypad Mode ESC > (V) Numeric Keypad Mode ESC # 8 (V) Fill Screen with E's ESC \ (A) String Terminator ESC ^ (A) Privacy Message String (Message Line) ESC ! Global Message String (Message Line) ESC k A.k.a. Definition String ESC P (A) Device Control String. Outputs a string directly to the host terminal without interpreta- tion. ESC _ (A) Application Program Command (Hardstatus) ESC ] 0 ; string ^G (A) Operating System Command (Hard- status, xterm title hack) ESC ] 83 ; cmd ^G (A) Execute screen command. This only works if multi-user sup- port is compiled into screen. The pseudo-user ":window:" is used to check the access con- trol list. Use "addacl :window: -rwx #?" to create a user with no rights and allow only the needed commands. Control-N (A) Lock Shift G1 (SO) Control-O (A) Lock Shift G0 (SI) ESC n (A) Lock Shift G2 ESC o (A) Lock Shift G3 ESC N (A) Single Shift G2 ESC O (A) Single Shift G3 ESC ( Pcs (A) Designate character set as G0 ESC ) Pcs (A) Designate character set as G1 ESC * Pcs (A) Designate character set as G2 ESC + Pcs (A) Designate character set as G3 ESC [ Pn ; Pn H Direct Cursor Addressing ESC [ Pn ; Pn f same as above ESC [ Pn J Erase in Display Pn = None or 0 From Cursor to End of Screen 1 From Beginning of Screen to Cursor 2 Entire Screen ESC [ Pn K Erase in Line Pn = None or 0 From Cursor to End of Line 1 From Beginning of Line to Cur- sor 2 Entire Line ESC [ Pn X Erase character ESC [ Pn A Cursor Up ESC [ Pn B Cursor Down ESC [ Pn C Cursor Right ESC [ Pn D Cursor Left ESC [ Pn E Cursor next line ESC [ Pn F Cursor previous line ESC [ Pn G Cursor horizontal position ESC [ Pn ` same as above ESC [ Pn d Cursor vertical position ESC [ Ps ;...; Ps m Select Graphic Rendition Ps = None or 0 Default Rendition 1 Bold 2 (A) Faint 3 (A) Standout Mode (ANSI: Itali- cized) 4 Underlined 5 Blinking 7 Negative Image 22 (A) Normal Intensity 23 (A) Standout Mode off (ANSI: Itali- cized off) 24 (A) Not Underlined 25 (A) Not Blinking 27 (A) Positive Image 30 (A) Foreground Black 31 (A) Foreground Red 32 (A) Foreground Green 33 (A) Foreground Yellow 34 (A) Foreground Blue 35 (A) Foreground Magenta 36 (A) Foreground Cyan 37 (A) Foreground White 39 (A) Foreground Default 40 (A) Background Black ... 49 (A) Background Default ESC [ Pn g Tab Clear Pn = None or 0 Clear Tab at Current Position 3 Clear All Tabs ESC [ Pn ; Pn r (V) Set Scrolling Region ESC [ Pn I (A) Horizontal Tab ESC [ Pn Z (A) Backward Tab ESC [ Pn L (A) Insert Line ESC [ Pn M (A) Delete Line ESC [ Pn @ (A) Insert Character ESC [ Pn P (A) Delete Character ESC [ Pn S Scroll Scrolling Region Up ESC [ Pn T Scroll Scrolling Region Down ESC [ Pn ^ same as above ESC [ Ps ;...; Ps h Set Mode ESC [ Ps ;...; Ps l Reset Mode Ps = 4 (A) Insert Mode 20 (A) Automatic Linefeed Mode 34 Normal Cursor Visibility ?1 (V) Application Cursor Keys ?3 (V) Change Terminal Width to 132 columns ?5 (V) Reverse Video ?6 (V) Origin Mode ?7 (V) Wrap Mode ?9 X10 mouse tracking ?25 (V) Visible Cursor ?1000 (V) VT200 mouse tracking ESC [ 5 i (A) Start relay to printer (ANSI Media Copy) ESC [ 4 i (A) Stop relay to printer (ANSI Media Copy) ESC [ 8 ; Ph ; Pw t Resize the window to `Ph' lines and `Pw' columns (SunView spe- cial) ESC [ c Send VT100 Identification String ESC [ x Send Terminal Parameter Report ESC [ > c Send VT220 Secondary Device Attributes String ESC [ 6 n Send Cursor Position Report