Commands Reference, Volume 6

xterm Command

Purpose

Provides a terminal emulator for the X Window System.

Note: The xterm command is ported from the Massachusetts Institute of Technology (MIT) X Window System, Version 11, Release 6 with no functional enhancements. The xterm command does not have support for localization or internationalization. For the localized and internationalized terminal emulator, the user can use the aixterm or dtterm commands.

Syntax

xterm [ -ToolkitOption ... ] [ -Option ... ]

Description

The xterm program is a terminal emulator for the X Window System. It provides DEC VT102 and Tektronix 4014 compatible terminals for programs that cannot use the window system directly. If the underlying operating system supports terminal resizing capabilities, the xterm program uses the facilities to notify programs running in the window whenever it is resized.

The VT102 and Tektronix 4014 terminals each have their own window so that you can edit text in one and look at graphics in the other at the same time. To maintain the correct aspect ratio (height/width), Tektronix graphics are restricted to the largest box with a 4014 aspect ratio that will fit in the window. This box is located in the upper left area of the window.

Although both windows may be displayed at the same time, one of them is considered the active window for receiving keyboard input and terminal output. This is the window that contains the text cursor. The active window can be chosen through escape sequences, the VT Options menu in the VT102 window, and the Tek Options menu in the 4014 window.

Emulations

The VT102 emulation is fairly complete, but does not support smooth scrolling, VT52 mode, the blinking character attribute, or the double-wide and double-size character sets. The termcap file entries that work with the xterm command include xterm, vt102, vt100 and ``ansi,'' and the xterm command automatically searches the termcap file in this order for these entries and then sets the TERM and the TERMCAP environment variables.

Many of the special xterm features may be modified under program control through a set of escape sequences different from the standard VT102 escape sequences.

The Tektronix 4014 emulation is also fairly good. It supports 12-bit graphics addressing, scaled to the window size. Four different font sizes and five different lines types are supported. There is no write-thru or defocused mode support.

The Tektronix text and graphics commands are recorded internally by the xterm command and may be written to a file by sending the COPY escape sequence (or through the Tektronix menu, as described in the following sections). The name of the file will be COPYyy-MM-dd.hh:mm:ss, where yy, MM, dd, hh, mm, and ss are the year, month, day, hour, minute, and second when the copy is performed (the file is created in the directory that the xterm command is started in, or the home directory for a login xterm).

Other Features

The xterm command automatically highlights the text cursor when the pointer enters the window (selected) and unhighlights it when the pointer leaves the window (unselected). If the window is the focus window, the text cursor is highlighted no matter where the pointer is located.

In VT102 mode, there are escape sequences to activate and deactivate an alternate screen buffer, which is the same size as the display area of the window. When activated, the current screen is saved and replaced with the alternate screen. Saving of lines scrolled off the top of the window is disabled until the normal screen is restored.

The termcap file entry for the xterm command allows the vi command editor to switch to the alternate screen for editing and to restore the screen on exit.

In either VT102 or Tektronix mode, there are escape sequences to change the name of the windows.

Options

The xterm terminal emulator accepts all of the standard X Toolkit command-line options as well as the following (if the option begins with a + instead of a -, the option is restored to its default value):

The following command-line arguments are provided for compatibility with older versions. They may not be supported in the next release as the X Toolkit provides standard options that accomplish the same task.

The following standard X Toolkit command-line arguments are commonly used with the xterm command:

Resources

The program understands all of the core X Toolkit resource names and classes as well as:

The following resources are specified as part of the vt100 widget (class VT100):

The following resources are specified as part of the tek4014 widget (class Tek4014):

The resources that may be specified for the various menus are described in the documentation for the Athena SimpleMenu widget. Following is a list of the names and classes of the entries in each of the menus.

The mainMenu has the following entries:

The vtMenu has the following entries:

The fontMenu has the following entries:

The tekMenu has the following entries:

The following resources are useful when specified for the Athena Scrollbar widget:

Pointer Usage

Once the VT102 window is created, the xterm command allows you to select text and copy it within the same or other windows.

The selection functions are invoked when the pointer buttons are used with no modifiers, and when they are used with the Shift key. The assignment of the functions to keys and buttons may be changed through the resource database.

Pointer button 1 (usually left) is used to save text into the cut buffer. Move the cursor to beginning of the text, and then hold the button down while moving the cursor to the end of the region and releasing the button. The selected text is highlighted and is saved in the global cut buffer and made the PRIMARY selection when the button is released.

Double-clicking selects by words, triple-clicking selects by lines, and quadruple-clicking goes back to characters. Multiple-click is determined by the amount of time from button up to button down, so you can change the selection unit in the middle of a selection. If the key or button bindings specify that an X selection is to be made, the xterm command will leave the selected text highlighted for as long as it is the selection owner.

Pointer button 2 (usually middle) "types" (pastes) the text from the PRIMARY selection, if any, otherwise from the cut buffer, inserting it as keyboard input.

Pointer button 3 (usually right) extends the current selection. If pressed while closer to the right edge of the selection than the left, it extends or contracts the right edge of the selection. If you contract the selection past the left edge of the selection, the xterm command assumes you really meant the left edge, restores the original selection, and then extends or contracts the left edge of the selection.

And the opposite also applies: if pressed while closer to the left edge of the selection than the right, it extends/contracts the left edge of the selection. If you contract the selection past the right edge of the selection, the xterm command assumes you really meant the right edge, restores the original selection, and then extends/contracts the right edge of the selection. Extension starts in the selection unit mode that the last selection or extension was performed in; you can multiple-click to cycle through them.

By cutting and pasting pieces of text without trailing new lines, you can take text from several places in different windows and form a command to the shell, for example, or take output from a program and insert it into your favorite editor. Since the cut buffer is globally shared among different applications, you should regard it as a "file" whose contents you know. The terminal emulator and other text programs should be treating it as if it were a text file; in other words, the text is delimited by new lines.

The scroll region displays the position and amount of text currently showing in the window (highlighted) relative to the amount of text actually saved. As more text is saved (up to the maximum), the size of the highlighted area decreases.

Clicking button 1 with the pointer in the scroll region moves the adjacent line to the top of the display window.

Clicking button 3 moves the top line of the display window down to the pointer position.

Clicking button 2 moves the display to a position in the saved text that corresponds to the pointer's position in the scrollbar.

Unlike the VT102 window, the Tektronix window does not allow the copying of text. It does allow Tektronix GIN mode, and in this mode the cursor will change from an arrow to a cross. Pressing any key will send that key and the current coordinates of the cross cursor. Pressing button one, two, or three will return the letters l, m, and r, respectively.

If the Shift key is pressed when a pointer button is pressed, the corresponding uppercase letter is sent. To distinguish a pointer button from a key, the high bit of the character is set (but this is bit is normally stripped unless the terminal mode is RAW; see the tty command for details).

Menus

The xterm command has four menus, named mainMenu, vtMenu, fontMenu, and tekMenu. Each menu pops up under the correct combinations of key and button presses. Most menus are divided into two section, separated by a horizontal line. The top portion contains various modes that can be altered. A check mark appears next to a mode that is currently active. Selecting one of these modes toggles its state. The bottom portion of the menu lists command entries; selecting one of these performs the indicated function.

The xterm menu pops up when the control key and pointer button one are pressed in a window. The mainMenu contains items that apply to both the VT102 and Tektronix windows. The Secure Keyboard mode is used when typing in passwords or other sensitive data in an unsecure environment.

Notable entries in the command section of the menu are Continue, Suspend, Interrupt, Hangup, Terminate, and Kill, which send the SIGCONT, SIGTSTP, SIGINT, SIGHUP, SIGTERM, and SIGKILL signals, respectively, to the process group of the process running under xterm (usually the shell). The Continue function is especially useful if the user has accidentally pressed Ctrl-Z, suspending the process.

The vtMenu sets various modes in the VT102 emulation, and is popped up when the control key and pointer button two are pressed in the VT102 window. In the command section of this menu, the soft reset entry will reset scroll regions. This can be convenient when some program has left the scroll regions set incorrectly (often a problem when using VMS or TOPS-20).

The full reset entry will clear the screen, reset tabs to every eight columns, and reset the terminal modes (such as wrap and smooth scroll) to their initial states just after the xterm command has finished processing the command-line options.

The fontMenu sets the font used in the VT102 window. In addition to the default font and a number of alternatives that are set with resources, the menu offers the font last specified by the Set Font escape sequence (See " Control Sequences" ) and the current selection as a font name (if the PRIMARY selection is owned).

The tekMenu sets various modes in the Tektronix emulation, and is popped up when the control key and pointer button two are pressed in the Tektronix window. The current font size is checked in the Modes section of the menu. The PAGE entry in the command section clears the Tektronix window.

Security

X windows environments differ in their security consciousness. MIT servers, run under xdm, are capable of using a magic cookie authorization scheme that can provide a reasonable level of security for many people. If your server is only using a host-based mechanism to control access to the server (see the xhost command), and if you enable access for a host and other users are also permitted to run clients on that same host, there is every possibility that someone can run an application that will use the basic services of the X protocol to snoop on your activities, potentially capturing a transcript of everything you type at the keyboard.

This is of particular concern when you want to type in a password or other sensitive data. The best solution to this problem is to use a better authorization mechanism than host-based control, but a simple mechanism exists for protecting keyboard input in the xterm command.

The xterm menu contains a Secure Keyboard entry that, when enabled, ensures that all keyboard input is directed only to the xterm command (using the GrabKeyboard protocol request). When an application prompts you for a password (or other sensitive data), you can enable Secure Keyboard using the menu, type in the data, and then disable Secure Keyboard using the menu again.

Only one X client at a time can secure the keyboard, so when you attempt to enable Secure Keyboard it may fail. In this case, the bell will sound. If the Secure Keyboard succeeds, the foreground and background colors will be exchanged (as if you selected the Reverse Video entry in the Modes menu); they will be exchanged again when you exit secure mode. If the colors do not switch, you should be very suspicious that you are being spoofed.

If the application you are running displays a prompt before asking for the password, it is safest to enter secure mode before the prompt gets displayed, and to make sure that the prompt gets displayed correctly (in the new colors), to minimize the probability of spoofing. You can also bring up the menu again and make sure that a check mark appears next to the entry.

Secure Keyboard mode will be disabled automatically if your xterm window becomes iconified (or otherwise unmapped), or if you start up a reparenting window manager (that places a title bar or other decoration around the window) while in Secure Keyboard mode. (This is a feature of the X protocol not easily overcome.) When this happens, the foreground and background colors will be switched back and the bell will sound in warning.

Character Classes

Clicking the middle mouse button twice in rapid succession will cause all characters of the same class (such as letters, white space, punctuation) to be selected. Since different people have different preferences for what should be selected (for example, should file names be selected as a whole or only the separate subnames), the default mapping can be overridden through the use of the charClass (class CharClass) resource.

This resource is a series of comma-separated range:value pairs. The range is either a single number or low-high in the range of 0 to 127, corresponding to the ASCII code for the character or characters to be set. The value is arbitrary, although the default table uses the character number of the first character occurring in the set.

The default table is:

static int charClass[128] = {
/* NUL  SOH  STX  ETX  EOT  ENQ  ACK  BEL */
    32,   1,   1,   1,   1,   1,   1,   1,
/*  BS   HT   NL   VT   NP   CR   SO   SI */
     1,  32,   1,   1,   1,   1,   1,   1,
/* DLE  DC1  DC2  DC3  DC4  NAK  SYN  ETB */
     1,   1,   1,   1,   1,   1,   1,   1,
/* CAN   EM  SUB  ESC   FS   GS   RS   US */
     1,   1,   1,   1,   1,   1,   1,   1,
/*  SP    !    "    #    $    %    &    ' */
    32,  33,  34,  35,  36,  37,  38,  39,
/*   (    )    *    +    ,    -    .    / */
    40,  41,  42,  43,  44,  45,  46,  47,
/*   0    1    2    3    4    5    6    7 */
    48,  48,  48,  48,  48,  48,  48,  48,
/*   8    9    :    ;    <    =    >    ? */
    48,  48,  58,  59,  60,  61,  62,  63,
/*   @    A    B    C    D    E    F    G */
    64,  48,  48,  48,  48,  48,  48,  48,
/*   H    I    J    K    L    M    N    O */
    48,  48,  48,  48,  48,  48,  48,  48,
/*   P    Q    R    S    T    U    V    W */
    48,  48,  48,  48,  48,  48,  48,  48,
/*   X    Y    Z    [    \    ]    ^    _ */
    48,  48,  48,  91,  92,  93,  94,  48,
/*   `    a    b    c    d    e    f    g */
    96,  48,  48,  48,  48,  48,  48,  48,
/*   h    i    j    k    l    m    n    o */
    48,  48,  48,  48,  48,  48,  48,  48,
/*   p    q    r    s    t    u    v    w */
    48,  48,  48,  48,  48,  48,  48,  48,
/*   x    y    z    {    |    }    ~  DEL */
    48,  48,  48, 123, 124, 125, 126,   1};

For example, the string 33:48,37:48,45-47:48,64:48 indicates that the exclamation mark, percent sign, dash, period, slash, and ampersand characters should be treated the same way as characters and numbers. This is useful for cutting and pasting electronic mailing addresses and file names.

Actions

It is possible to rebind keys (or sequences of keys) to arbitrary strings for input by changing the translations for the vt100 or tek4014 widgets. Changing the translations for events other than key and button events is not expected, and will cause unpredictable behavior. The following actions are provided for using within the vt100 or tek4014 translations resources:

The Tektronix window also has the following action:

The default bindings in the VT102 window are:

Shift <KeyPress> Prior:     scroll-back(1,halfpage) \n\
Shift <KeyPress> Next:      scroll-forw(1,halfpage) \n\
Shift <KeyPress> Select:    select-cursor-start \
                            select-cursor-end(PRIMARY,
                            CUT_BUFFER0) \n\
Shift <KeyPress> Insert:    insert-selection(PRIMARY,
                            CUT_BUFFER0) \n\
~Meta<KeyPress>:            insert-seven-bit \n\
Meta<KeyPress>:             insert-eight-bit \n\
!Ctrl <Btn1Down>:           popup-menu(mainMenu) \n\
!Lock Ctrl <Btn1Down>:      popup-menu(mainMenu) \n\
~Meta <Btn1Down>:           select-start \n\
~Meta <Btn1Motion>:         select-extend \n\
!Ctrl <Btn2Down>:           popup-menu(vtMenu) \n\
!Lock Ctrl <Btn2Down>:      popup-menu(vtMenu) \n\
~Ctrl ~Meta <Btn2Down>:     ignore \n\
~Ctrl ~Meta <Btn2Up>:       insert-selection(PRIMARY,
                            CUT_BUFFER0) \n\
!Ctrl <Btn3Down>:           popup-menu(fontMenu) \n\
!Lock Ctrl <Btn3Down>:      popup-menu(fontMenu) \n\
~Ctrl ~Meta <Btn3Down>:     start-extend \n\
~Meta <Btn3Motion>:         select-extend \n\
<BtnUp>:                    select-end(PRIMARY, CUT_BUFFER0) \n\
<BtnDown>:                  bell(0)

The default bindings in the Tektronix window are:

~Meta<KeyPress>:            insert-seven-bit \n\
Meta<KeyPress>:             insert-eight-bit \n\
!Ctrl <Btn1Down>:           popup-menu(mainMenu) \n\
!Lock Ctrl <Btn1Down>:      popup-menu(mainMenu) \n\
!Ctrl <Btn2Down>:           popup-menu(tekMenu) \n\
!Lock Ctrl <Btn2Down>:      popup-menu(tekMenu) \n\
Shift ~Meta<Btn1Down>:      gin-press(L) \n\
~Meta<Btn1Down>:            gin-press(l) \n\
Shift ~Meta<Btn2Down>:      gin-press(M) \n\
~Meta<Btn2Down>:            gin-press(m) \n\
Shift ~Meta<Btn3Down>:      gin-press(R) \n\
~Meta<Btn3Down>:            gin-press(r)

The following is an example of how the keymap action is used to add special keys for entering commonly typed works:

*VT100.Translations:          #override <Key>F13: keymap(dbx)
*VT100.dbxKeymap.translations:
 \
 
    <Key>F14:    keymap(None) \n\
    <Key>F17:    string("next") string(0x0d) \n\
    <Key>F18:    string("step") string(0x0d) \n\
    <Key>F19:    string("continue") string(0x0d) \n\
    <Key>F20:    string("print ")
                 insert-selection(PRIMARY,CUT_BUFFER0)

Environment

The xterm command sets the environment variables TERM and TERMCAP properly for the size window you have created. It also uses and sets the DISPLAY environment variable to specify which bitmap display terminal to use. The WINDOWID environment variable is set to the X window ID number of the xterm window.

Bugs

Large pastes do not work on some systems. This is not a bug in the xterm command; it is a bug in the pseudo terminal driver of those systems. The xterm command feeds large pastes to the pty only as fast as the pty will accept data, but some pty drivers do not return enough information to know if the write operation has succeeded.

Many of the options are not resettable after the xterm command starts.

Only fixed-width, character-cell fonts are supported.

Control Sequences

This section lists control sequences available for the xterm command.

Definitions

The following figure shows how to interpret key sequences in this section.

VT100 Mode

Most of these control sequences are standard VT102 control sequences, but there are some sequences here from later DEC VT terminals, too. Major VT102 features not supported are smooth scrolling, double-size characters, blinking characters, and VT52 mode.

There are additional control sequences to provide xterm-dependent functions, like the scrollbar or window size. Where the function is specified by DEC or ISO 6429, the code assigned to it is given in parentheses. The escape codes to designate character sets are specified by ISO 2022; see that document for a discussion of character sets.

XTERM Description Limitation

The xterm terminal description in the DEC.TI file on AIX Version 4 provides underline mode by using the SGR attribute. The SMUL and RMUL attributes are not currently defined in the XTERM terminal description on AIX Version 4. Use the more generic capability named SGR.

tput sgr x y

Where x is either a 1 or a 0 to turn standout mode on or off respectively, and y is either a 1 or a 0 to turn underline mode on or off respectively. See the article "terminfo file format" for more details on the SGR capability.

tput sgr 0 1    turn off standout; turn on underline
tput sgr 0 0    turn off standout; turn off underline
tput sgr 1 1    turn on standout; turn on underline
tput sgr 1 0    turn on standout; turn off underline

Mouse Tracking

The VT widget can be set to send the mouse position and other information on button presses. These modes are typically used by editors and other full-screen applications that want to make use of the mouse.

There are three mutually exclusive modes, each enabled (or disabled) by a different parameter in the DECSET (or DECRST) escape sequence. Parameters for all mouse tracking escape sequences generated by the xterm command encode numeric parameters in a single character as value+040. The screen coordinate system is 1-based.

For example ! is 1. The screen screen coordinate system is 1-based.

X10 compatibility mode sends an escape sequence on button press encoding the location and the mouse button pressed. It is enabled by specifying parameter 9 to DECSET. On button press, the xterm command sends the following "6 characters" . Cb is button-1. Cx and Cy are the x and y coordinates of the mouse when the button was pressed.

ESC [ M C_bC_xC_y

Normal tracking mode sends an escape sequence on both button press and release. Modifier information is also sent. It is enabled by specifying parameter 1000 to DECSET. On button press or release, the xterm command sends the following "key sequence" :

ESC [ M C_bC_xC_y

The low two bits of C_b encode button information: 0=MB1 pressed, 1=MB2 pressed, 2=MB3 pressed, 3=release. The upper bits encode what modifiers were down when the button was pressed and are added together. 4=Shift, 8=Meta, 16=Control. C_x and C_y are the x and y coordinates of the mouse event. The upper left corner is (1,1).

Mouse hilite tracking notifies a program of a button press, receives a range of lines from the program, highlights the region covered by the mouse within that range until button release, and then sends the program the release coordinates. It is enabled by specifying parameter 1001 to DECSET.

Attention: Use of this mode requires a cooperating program or it will hang the xterm command. On button press, the same information as for normal tracking is generated; the xterm command then waits for the program to send mouse tracking information. All X events are ignored until the following proper escape sequence is received from the pty:

ESC [ P_s ; P_s ; P_s ; P_s ; T

The parameters are Func, Startx, Starty, FirstRow, and LastRow. The Func parameter is nonzero to initiate hilite tracking and 0 (zero) to abort. The Startx and Starty parameters give the starting x and y location for the highlighted region. The ending location tracks the mouse, but is never above row FirstRow and is always above row LastRow. (The top of the screen is row 1.) When the button is released, the xterm command reports the ending position one of two ways: if the start and end coordinates are valid text locations, the xterm command reports the "ending position" as follows:

ESC [ t C_xC_y

If either coordinate is past the end of the line, the xterm command reports the "ending position" as follows:

ESC [ T C_xC_yC_xC_yC_xC_y

The parameters are Startx, Starty, Endx, Endy, Mousex, and Mousey. The Startx, Starty, Endx, and Endy parameters give the starting and ending character positions of the region. The Mousex and Mousey parameters give the location of the mouse at button up, which may not be over a character.

Tektronix 4014 Mode

Most of these sequences are standard Tektronix 4014 control sequences. The major features missing are the write-thru and defocused modes. This document does not describe the commands used in the various Tektronix plotting modes but does describe the commands to switch modes.

Related Information

The aixterm command, resize command, tset command, vi or vedit command.