20. Miscellaneous commands

The commands described here do not fit well under any of the other categories.

20.1 At

Command: at [identifier][#|*|%] command [args]

(none)
Execute a command at other displays or windows as if it had been entered there. At changes the context (the `current window' or `current display' setting) of the command. If the first parameter describes a non-unique context, the command will be executed multiple times. If the first parameter is of the form `identifier*' then identifier is matched against user names. The command is executed once for each display of the selected user(s). If the first parameter is of the form `identifier%' identifier is matched against displays. Displays are named after the ttys they attach. The prefix `/dev/' or `/dev/tty' may be omitted from the identifier. If identifier has a # or nothing appended it is matched against window numbers and titles. Omitting an identifier in front of the #, * or % character selects all users, displays or windows because a prefix-match is performed. Note that on the affected display(s) a short message will describe what happened. Note that the # character works as a comment introducer when it is preceded by whitespace. This can be escaped by prefixing # with a \. Permission is checked for the initiator of the at command, not for the owners of the affected display(s). Caveat: When matching against windows, the command is executed at least once per window. Commands that change the internal arrangement of windows (like other) may be called again. In shared windows the command will be repeated for each attached display. Beware, when issuing toggle commands like login! Some commands (e.g. \*Qprocess) require that a display is associated with the target windows. These commands may not work correctly under at looping over windows.

20.2 Break

Command: break [duration]

(none)
Send a break signal for duration*0.25 seconds to this window. For non-Posix systems the time interval is rounded up to full seconds. Most useful if a character device is attached to the window rather than a shell process (see section 6.6 Window Types). The maximum duration of a break signal is limited to 15 seconds.

Command: pow_break

(none)
Reopen the window's terminal line and send a break condition.

Command: breaktype [tcsendbreak|TIOCSBRK|TCSBRK]

(none)
Choose one of the available methods of generating a break signal for terminal devices. This command should affect the current window only. But it still behaves identical to defbreaktype. This will be changed in the future. Calling breaktype with no parameter displays the break setting for the current window.

Command: defbreaktype [tcsendbreak|TIOCSBRK|TCSBRK]

(none)
Choose one of the available methods of generating a break signal for terminal devices opened afterwards. The preferred methods are tcsendbreak and TIOCSBRK. The third, TCSBRK, blocks the complete screen session for the duration of the break, but it may be the only way to generate long breaks. tcsendbreak and TIOCSBRK may or may not produce long breaks with spikes (e.g. 4 per second). This is not only system dependant, this also differs between serial board drivers. Calling defbreaktype with no parameter displays the current setting.

20.3 Debug

Command: debug [on|off]

(none)
Turns runtime debugging on or off. If screen has been compiled with option -DDEBUG debugging is available and is turned on per default. Note that this command only affects debugging output from the main `SCREEN' process correctly. Debug output from attacher processes can only be turned off once and forever.

20.4 License

Command: license

(none)
Display the disclaimer page. This is done whenever screen is started without options, which should be often enough.

20.5 Nethack

Command: nethack state

(none)
Changes the kind of error messages used by screen. When you are familiar with the game nethack, you may enjoy the nethack-style messages which will often blur the facts a little, but are much funnier to read. Anyway, standard messages often tend to be unclear as well.

This option is only available if screen was compiled with the NETHACK flag defined (see section 26. Installation). The default setting is then determined by the presence of the environment variable $NETHACKOPTIONS.

20.6 Nonblock

Command: nonblock [state|numsecs]

Tell screen how to deal with user interfaces (displays) that cease to accept output. This can happen if a user presses ^S or a TCP/modem connection gets cut but no hangup is received. If nonblock is off (this is the default) screen waits until the display restarts to accept the output. If nonblock is on, screen waits until the timeout is reached (on is treated as 1s). If the display still doesn't receive characters, screen will consider it "blocked" and stop sending characters to it. If at some time it restarts to accept characters, screen will unblock the display and redisplay the updated window contents.

Command: defnonblock state|numsecs

Same as the nonblock command except that the default setting for displays is changed. Initial setting is off.

20.7 Number

Command: number [n]

(C-a N)
Change the current window's number. If the given number n is already used by another window, both windows exchange their numbers. If no argument is specified, the current window number (and title) is shown.

20.8 Silence

Command: silence [state|sec]

(none)
Toggles silence monitoring of windows. When silence is turned on and an affected window is switched into the background, you will receive the silence notification message in the status line after a specified period of inactivity (silence). The default timeout can be changed with the silencewait command or by specifying a number of seconds instead of on or off. Silence is initially off for all windows.

Command: defsilence state

(none)
Same as the silence command except that the default setting for new windows is changed. Initial setting is `off'.

Command: silencewait seconds

(none)
Define the time that all windows monitored for silence should wait before displaying a message. Default is 30 seconds.

20.9 Time

Command: time [string]

(C-a t, C-a C-t)
Uses the message line to display the time of day, the host name, and the load averages over 1, 5, and 15 minutes (if this is available on your system). For window-specific information use info (see section 11.6 Info). If a string is specified, it changes the format of the time report like it is described in the string escapes chapter (see section 21. String Escapes). Screen uses a default of `%c:%s %M %d %H%? %l%?'.

20.10 Verbose

Command: verbose [on|off]

If verbose is switched on, the command name is echoed, whenever a window is created (or resurrected from zombie state). Default is off. Without parameter, the current setting is shown.

20.11 Version

Command: version

(C-a v)
Display the version and modification date in the message line.

20.12 Zombie

Command: zombie [keys]

Command: defzombie [keys]

(none)
Per default windows are removed from the window list as soon as the windows process (e.g. shell) exits. When a string of two keys is specified to the zombie command, `dead' windows will remain in the list. The kill command may be used to remove the window. Pressing the first key in the dead window has the same effect. Pressing the second key, however, screen will attempt to resurrect the window. The process that was initially running in the window will be launched again. Calling zombie without parameters will clear the zombie setting, thus making windows disappear when the process terminates.

As the zombie setting is affected globally for all windows, this command should only be called defzombie. Until we need this as a per window setting, the commands zombie and defzombie are synonymous.

20.13 Printcmd

Command: printcmd [cmd]

(none)
If cmd is not an empty string, screen will not use the terminal capabilities po/pf for printing if it detects an ansi print sequence ESC [ 5 i, but pipe the output into cmd. This should normally be a command like `lpr' or `cat > /tmp/scrprint'. Printcmd without an argument displays the current setting. The ansi sequence ESC \ ends printing and closes the pipe.

Warning: Be careful with this command! If other user have write access to your terminal, they will be able to fire off print commands.

20.14 Sorendition

Command: sorendition [attr [color]]

(none)
Change the way screen does highlighting for text marking and printing messages. See the chapter about string escapes (see section 21. String Escapes) for the syntax of the modifiers. The default is currently `=s dd' (standout, default colors).

20.15 Attrcolor

Command: attrcolor attrib [attribute/color-modifier]

(none)
This command can be used to highlight attributes by changing the color of the text. If the attribute attrib is in use, the specified attribute/color modifier is also applied. If no modifier is given, the current one is deleted. See the chapter about string escapes (see section 21. String Escapes) for the syntax of the modifier. Screen understands two pseudo-attributes, i stands for high-intensity foreground color and I for high-intensity background color.

Examples:

attrcolor b "R"

Change the color to bright red if bold text is to be printed.

attrcolor u "-u b"

Use blue text instead of underline.

attrcolor b ".I"

Use bright colors for bold text. Most terminal emulators do this already.

attrcolor i "+b"

Make bright colored text also bold.

20.16 Setsid

Command: setsid state

(none)
Normally screen uses different sessions and process groups for the windows. If setsid is turned off, this is not done anymore and all windows will be in the same process group as the screen backend process. This also breaks job-control, so be careful. The default is on, of course. This command is probably useful only in rare circumstances.

20.17 Eval

Command: eval command1 [command2 ...]

(none)
Parses and executes each argument as separate command.

20.18 Maxwin

Command: maxwin n

(none)
Set the maximum window number screen will create. Doesn't affect already existing windows. The number may only be decreased.

20.19 Backtick

Command: backtick id lifespan autorefresh command [args]

Command: backtick id

(none)
Program the backtick command with the numerical id id. The output of such a command is used for substitution of the %` string escape (see section 21. String Escapes). The specified lifespan is the number of seconds the output is considered valid. After this time, the command is run again if a corresponding string escape is encountered. The autorefresh parameter triggers an automatic refresh for caption and hardstatus strings after the specified number of seconds. Only the last line of output is used for substitution.

If both the lifespan and the autorefresh parameters are zero, the backtick program is expected to stay in the background and generate output once in a while. In this case, the command is executed right away and screen stores the last line of output. If a new line gets printed screen will automatically refresh the hardstatus or the captions.

The second form of the command deletes the backtick command with the numerical id id.

20.20 Screen Saver

Command: idle [timeout [cmd args]]

(none)
Sets a command that is run after the specified number of seconds inactivity is reached. This command will normally be the blanker command to create a screen blanker, but it can be any screen command. If no command is specified, only the timeout is set. A timeout of zero (ot the special timeout off) disables the timer. If no arguments are given, the current settings are displayed.

Command: blanker

(none)
Activate the screen blanker. First the screen is cleared. If no blanker program is defined, the cursor is turned off, otherwise, the program is started and it's output is written to the screen. The screen blanker is killed with the first keypress, the read key is discarded.

This command is normally used together with the idle command.

Command: blankerprg [program args]

Defines a blanker program. Disables the blanker program if no arguments are given.

20.21 Zmodem

Command: zmodem [off|auto|catch|pass]

Command: zmodem sendcmd [string]

Command: zmodem recvcmd [string]

(none)
Define zmodem support for screen. Screen understands two different modes when it detects a zmodem request: pass and catch. If the mode is set to pass, screen will relay all data to the attacher until the end of the transmission is reached. In catch mode screen acts as a zmodem endpoint and starts the corresponding rz/sz commands. If the mode is set to auto, screen will use catch if the window is a tty (e.g. a serial line), otherwise it will use pass.

You can define the templates screen uses in catch mode via the second and the third form.

Note also that this is an experimental feature.