Term::ReadKey − A perl module for simple terminal control


        use Term::ReadKey;
        ReadMode 4; # Turn off controls keys
        while (not defined ($key = ReadKey(−1))) {
                # No key yet
        print "Get key $key\n";
        ReadMode 0; # Reset tty mode before exiting


Term::ReadKey is a compiled perl module dedicated to providing simple control over terminal driver modes (cbreak, raw, cooked, etc.,) support for non-blocking reads, if the architecture allows, and some generalized handy functions for working with terminals. One of the main goals is to have the functions as portable as possible, so you can just plug in "use Term::ReadKey" on any architecture and have a good likelyhood of it working.
ReadMode MODE [, Filehandle]

Takes an integer argument, which can currently be one of the following values:

    0    Restore original settings.
    1    Change to cooked mode.
    2    Change to cooked mode with echo off.
          (Good for passwords)
    3    Change to cbreak mode.
    4    Change to raw mode.
    5    Change to ultra−raw mode.
          (LF to CR/LF translation turned off)
    Or, you may use the synonyms:

These functions are automatically applied to the STDIN handle if no other handle is supplied. Modes 0 and 5 have some special properties worth mentioning: not only will mode 0 restore original settings, but it cause the next ReadMode call to save a new set of default settings. Mode 5 is similar to mode 4, except no CR/LF translation is performed, and if possible, parity will be disabled (only if not being used by the terminal, however. It is no different from mode 4 under Windows.)

If you are executing another program that may be changing the terminal mode, you will either want to say

    ReadMode 1
    ReadMode 1;

which resets the settings after the program has run, or:

    ReadMode 0;
    ReadMode 1;

which records any changes the program may have made, before resetting the mode.

ReadKey MODE [, Filehandle]

Takes an integer argument, which can currently be one of the following values:

    0    Perform a normal read using getc
    −1   Perform a non−blocked read
    >0   Perform a timed read

(If the filehandle is not supplied, it will default to STDIN .) If there is nothing waiting in the buffer during a non-blocked read, then undef will be returned. Note that if the OS does not provide any known mechanism for non-blocking reads, then a "ReadKey −1" can die with a fatal error. This will hopefully not be common.

If MODE is greater then zero, then ReadKey will use it as a timeout value in seconds (fractional seconds are allowed), and won’t return "undef" until that time expires. (Note, again, that some OS ’s may not support this timeout behaviour.) If MODE is less then zero, then this is treated as a timeout of zero, and thus will return immediately if no character is waiting. A MODE of zero, however, will act like a normal getc.

There are currently some limitations with this call under Windows. It may be possible that non-blocking reads will fail when reading repeating keys from more then one console.

ReadLine MODE [, Filehandle]

Takes an integer argument, which can currently be one of the following values:

    0    Perform a normal read using scalar(<FileHandle>)
    −1   Perform a non−blocked read
    >0   Perform a timed read

If there is nothing waiting in the buffer during a non-blocked read, then undef will be returned. Note that if the OS does not provide any known mechanism for non-blocking reads, then a "ReadLine 1" can die with a fatal error. This will hopefully not be common. Note that a non-blocking test is only performed for the first character in the line, not the entire line. This call will probably not do what you assume, especially with ReadMode’s higher then 1. For example, pressing Space and then Backspace would appear to leave you where you started, but any timeouts would now be suspended.

This call is currently not available under Windows.

GetTerminalSize [Filehandle]

Returns either an empty array if this operation is unsupported, or a four element array containing: the width of the terminal in characters, the height of the terminal in character, the width in pixels, and the height in pixels. (The pixel size will only be valid in some environments.)

Under Windows, this function must be called with an "output" filehandle, such as STDOUT , or a handle opened to CONOUT$ .

SetTerminalSize WIDTH ,HEIGHT,XPIX,YPIX [, Filehandle]

Return −1 on failure, 0 otherwise. Note that this terminal size is only for informative value, and changing the size via this mechanism will not change the size of the screen. For example, XTerm uses a call like this when it resizes the screen. If any of the new measurements vary from the old, the OS will probably send a SIGWINCH signal to anything reading that tty or pty.

This call does not work under Windows.

GetSpeeds [, Filehandle]

Returns either an empty array if the operation is unsupported, or a two value array containing the terminal in and out speeds, in decimal. E.g, an in speed of 9600 baud and an out speed of 4800 baud would be returned as (9600,4800). Note that currently the in and out speeds will always be identical in some OS ’s. No speeds are reported under Windows.

GetControlChars [, Filehandle]

Returns an array containing key/value pairs suitable for a hash. The pairs consist of a key, the name of the control character/signal, and the value of that character, as a single character. This call does nothing under Windows.

Each key will be an entry from the following list:


Thus, the following will always return the current interrupt character, regardless of platform.

        %keys = GetControlChars;
        $int = $keys{INTERRUPT};

SetControlChars [, Filehandle]

Takes an array containing key/value pairs, as a hash will produce. The pairs should consist of a key that is the name of a legal control character/signal, and the value should be either a single character, or a number in the range 0−255. SetControlChars will die with a runtime error if an invalid character name is passed or there is an error changing the settings. The list of valid names is easily available via

        %cchars = GetControlChars();
        @cnames = keys %cchars;

This call does nothing under Windows.


Kenneth Albanowski <>

Currently maintained by Jonathan Stowe <>


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