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GNU screen [terminal]

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Terminal Manipulations

Basics

Extras

screen is flexible about flow control. Traditionally, some terminals do flow control in-band, using ^S when they want to stop the flow data and ^Q when they want it to resume. On the other hand, some programs (such as emacs) use those keys for other purposes. If flow control is turned on in screen, ^S will stop screen from sending anything more to your terminal and ^Q will resume. Turning flow control off allows those characters to pass through to your programs. The default setting is “auto”, which attempts to determine if flow control is needed or not. screen is generally pretty good at figuring this out.

screen can deal with multiple character sets and character encodings. The encoding and defencoding commands can be used to set window encodings or override the detected terminal encoding. If the display's and window's encodings differ, screen will translate between the two. Characters not in the display's charset are represented by question marks. screen does its own encoding and only supports a handful of encodings. As of version 4.0.2, those are: C, eucJP, SJIS, eucKR, eucCN, Big5, KOI8-R, CP1251, UTF-8, ISO8859-2, ISO8859-3, ISO8859-4, ISO8859-5, ISO8859-6, ISO8859-7, ISO8859-8, ISO8859-9, ISO8859-10, ISO8859-15, jis, and GBK. [This somehow ties in with the charset setting, but I don't understand that one. <PMG>]

You can alter various aspects of screen's use of termcap and terminfo, via the termcap, terminfo, and termcapinfo commands. All three have the same syntax. Using termcapinfo is recommended, since that affects both termcap and terminfo settings. Note that all three require the use of termcap names; terminfo-style long names are not supported. The most common use of these commands is to change how screen treats display terminals. If you want to change a termcap setting for, say, xterms, you can use the termcapinfo command to change the termcap definition that screen uses for that terminal type. This affects only screen, and can be used to effect changes when you don't want to or can't change the system terminal definitions. There are also several special terminal capabilities that are screen-specific. See the “Examples” section for, well, examples. The other use is to change the terminal capbilities of screen's virtual terminal. This can be useful to alter how other programs interact with screen, without having to edit screen's source code and recompile. [This is ugly. I need to rewrite it to make it clearer. <PMG>]

Command Line

  • -a - “include all capabilities (with some minor exceptions) in each window's termcap, even if screen must redraw parts of the display in order to implement a function.”
  • -A - Resize windows to fit the current terminal. Only effective if screen would otherwise try to resize your terminal to fit the windows.
  • -f, -fn, -fa - Respectively, set flow control on, off, or automatic. Same as defflow.
  • -O - “selects a more optimal output mode for your terminal rather than true VT100 emulation (only affects auto-margin terminals without 'LP'). This can also be set in your .screenrc by specifying 'OP' in a termcap command.”
  • -T term - Changes the $TERM setting for a session (if used outside screen) or window (from within screen). Same as term.
  • -U - Run screen in UTF-8 mode. screen assumes that it can output UTF-8 (normally it checks locale settings) and sets defutf8 on.

Keybindings

  • C-a C-b - (break) Sends a break signal to the current window.
  • C-a B - (pow_break) Closes and reopens the terminal and sends a break signal.
  • C-a f - (flow) Toggle flow setting between on, off, and auto.
  • C-a q - (xon) Sends an XON (^Q) to the current window.
  • C-a r - (wrap) Toggle the current window's line-wrap setting.
  • C-a S - (xoff) Sends an XOFF (^S) to the current window.
  • C-a W - (width) Toggle terminal between 80 and 132 columns.
  • C-a Z - (reset) Reset the window's terminal settings to its defaults.
  • C-a . - (dumptermcap) Write out a .termcap file.

Commands

  • allpartial on|off - Global command equivalent to setting partial for all current windows. Default is off.
  • altscreen on|off - Enables “alternate screen” support (ti and te termcap settings) for screen windows. Does not change existing windows. Default is off.
  • bce [on|off] - Set or toggle background-color-erase setting. “If bce is set to on, all characters cleared by an erase/insert/scroll/clear operation will be displayed in the current background color. Otherwise the default background color is used.” Most noticeable when your terminal's “default” background is different from the current background color, such as an xterm with a background image. [What's the default setting? <PMG>]
  • c1 [on|off] - Sets or toggles c1 code processing. If on, characters with the high bit set will be treated as an ESC followed by the corresponding 7-bit character. Default is off.
  • charset set - “Change the current character set slot designation and charset mapping. The first four character of set are treated as charset designators while the fifth and sixth character must be in range 0 to 3 and set the GL/GR charset mapping. On every position a '.' may be used to indicate that the corresponding charset/mapping should not be changed (set is padded to six characters internally by appending '.' chars). New windows have BBBB02 as default charset, unless an encoding command is active.” [I don't really understand this. It's obviously terminal charset munging, but I don't get the particulars–I just use UTF-8. <PMG>]
  • defbce on|off - Same as bce, but sets the default setting for new windows.
  • defbreaktype [tcsendbreak|TIOCSBRK|TCSBRK] - Sets the type of break signal sent via the break or pow_break command. Recommended settings are tcsendbreak and TIOCSBRK. TCSBRK blocks the whole session, but may be the only way to get long breaks. [The man page is somewhat light on detail here. Clarifications appreciated. <PMG>]
  • defc1 on|off - Same as c1, but sets the default setting for new windows.
  • defcharset [set] - Same as charset, but sets the default setting for new windows.
  • defflow on|off|auto [interrupt] - Same as flow, but sets the default setting for new windows.
  • defgr on|off - Same as gr, but sets the default setting for new windows.
  • defencoding enc - Same as encoding, but sets the default setting for new windows.
  • defnonblock on|off|numsecs - Same as nonblock, but sets the default setting for new displays.
  • defutf8 on|off - Same as utf8, but sets the default setting for new windows.
  • defwrap on|off - Same as wrap, but sets the default setting for new windows.
  • dinfo - Shows what settings screen is using for the current display. As of screen 4.0.2 shows: display dimensions (columns, rows), encoding, whether the display is an xterm, whether the display supports color, and what charset is in use (one of iso2022 or altchar).
  • dumptermcap - Tells screen to create a .termcap file in its socket directory. The file will contain all the termcap settings for screen's virtual terminal. It's the same as the $TERMCAP environment variable that screen sets, but can be used for programs that don't understand $TERMCAP.
  • encoding enc [enc] - Set the character encoding for the current window. The second argument sets the character encoding for the current display (and is rarely needed because screen can usually tell from its locale settings).
  • flow [on|off|auto] - Sets the current window's flow control mode.
  • gr [on|off] - Sets or toggles GR charset switching. If on, when asked to display a character with the 8th bit set, screen uses the GR charset. While necessary for some terminals, it is not compatible with 8-bit encodings (such as ISO8859-1) and dfaults to off.
  • nonblock [on|off|numsecs] - Sets or toggles screen's behavior when a display stops receiving characters. When off, screen blocks on sending to the terminal; in some situations this can freeze the entire session. When on, screen waits the specified timeout (on is equivalent to 1 second); if the display still does not respond, screen stops sending to it until it recovers. Default is off.
  • partial on|off - Sets whether screen should draw the entire window when switching windows. If on, screen will blank the display and then draw only the line that the cursor is on. Useful for slow terminals. Default is off.
  • printcmd [cmd] - Shows or sets the command used for handling the ANSI print sequence ESC [ 5 i. If set, the text to be printed will be given to the command on standard input. If unset, screen will use the po and pf terminal capabilities to tell the display terminal to print the text. Default is unset.
  • reset - Resets the current window's virtual terminal settings to their default settings. Only affects changes made by escape sequences (things like scrolling regions, color settings, etc.), not changes made by screen commands. Effectively the same as power-cycling a physical terminal.
  • term term - Changes the value of $TERM that screen passes to its windows' child processes. Useful when the default, 'screen', is unknown to a system. Be careful to set it to a compatible value; 'vt100' is recommended.
  • [termcap|terminfo|termcapinfo] term terminal-tweaks [window-tweaks] - Tweaks termcap entries for either screen's interaction with the display terminal (terminal-tweaks) or for the virtual terminal presented to child programs (window-tweaks). See “Extras” section for discussion.
  • utf8 [on|off [on|off]] - Changes or toggles the encoding on the current window. The second parameter changes the UTF-8 setting of the display. (The -U option is the preferred way to set that, however.) [Is this merely equivalent to encoding UTF-8? <PMG>]
  • wrap [on|off] - Sets or toggles the current window's line wrap setting. When on, characters displayed while the cursor is at the end of the line will cause the cursor to wrap to the next line. When off, the cursor will stay at the end of the line, and the characters will overwrite each other. Default is on.
  • zmodem [off|auto|catch|pass] - Sets screen's handling of zmodem communcations. pass means that screen will not do anything to zmodem streams and will relay them to the display terminal. catch means that screen will catch and intermret the streams itself; the display terminal will not see them. auto attempts to determine what the correct setting is; it uses catch if the display is a tty and pass if the display is a pseudoterminal. [But what does off mean? <PMG>] This is an experimental feature.
  • zmodem sendcmd|recvcmd [string] - Sets the templates used when in catch mode for the zmodem protocol.

Examples

Upon being asked to print a block of text, save it to a file in the user's ome directory:

printcmd "cat > ${HOME}/screenprint"

Upon being asked to print a block of text, print it via lpr:

printcmd lpr

Set the LP capability (the last screen position can be updated) and remove the hs capability (presence of a hardstatus line) from terminals that start with “xterm”:

termcap xterm* LP:hs@

On VT102s and VT220s, set the escape characters to enter (Z0) and exit (Z1) 132-column mode:

termcap vt102|vt220 Z0=\E[?3h:Z1=\E[?3l

Add function key labels to the termcap entries for screen's virtual terminal. For purposes of modifying the windows' termcap entries, the term-type specified doesn't matter.

termcap vt100 "" l0=PF1:l1=PF2:l2=PF3:l3=PF4

Abuse screen's hardstatus support to put things in xterm titlebars. This tells screen that xterms (and related terminals) have a hardstatus line (hs) and sets the escape sequences for entering (ts) and leaving (fs) the hardstatus to the sequences for entering and leaving the titlebar. To go with that, uses defhstatus to set a default message and hardstatus off to tell screen not to use the hardstatus line for screen messages:

termcapinfo xterm*|rxvt|gnome-terminal|konsole|kterm|Eterm 'hs:ts=\E]0;:fs=\007'
defhstatus "screen ^E (^Et) | $USER@^EH"
hardstatus off

(FAQ) Turns off alternate screen switching in xterms, so that text in screen will go into the xterm's scrollback buffer:

termcapinfo xterm ti@:te@

Uses screen's output translation capability (XC) to rot-13 all output. (Will not work in UTF-8 mode, apparently.):

termcapinfo * XC=B%,an,AN,bo,BO,cp,CP,dq,DQ,er,ER,fs,FS,gt,GT,hu,HU,iv,IV,jw,JW,kx,KX,ly,LY,mz,MZ,na,NA,ob,OB,pc,PC,qd,QD,re,RE,sf,SF,tg,TG,uh,UH,vi,VI,wj,WJ,xk,XK,yl,YL,zm,ZM
 
terminal.1182617485.txt.gz · Last modified: 2007/08/16 10:33 (external edit)
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