Paul Evans


IO::Termios - supply termios(3) methods to IO::Handle objects


 use IO::Termios;

 my $term = IO::Termios->open( "/dev/ttyS0", "9600,8,n,1" )
    or die "Cannot open ttyS0 - $!";

 $term->print( "Hello world\n" ); # Still an IO::Handle

 while( <$term> ) {
    print "A line from ttyS0: $_";


This class extends the generic IO::Handle object class by providing methods which access the system's terminal control termios(3) operations. These methods are primarily of interest when dealing with TTY devices, including serial ports.

The flag-setting methods will apply to any TTY device, such as a pseudo-tty, and are useful for controlling such flags as the ECHO flag, to disable local echo.

 my $stdin = IO::Termios->new( \*STDIN );
 $stdin->setflag_echo( 0 );

When dealing with a serial port the line mode method is useful for setting the basic serial parameters such as baud rate, and the modem line control methods can be used to access the hardware handshaking lines.

 my $ttyS0 = IO::Termios->open( "/dev/ttyS0" );
 $ttyS0->set_mode( "19200,8,n,1" );
 $ttyS0->set_modem({ dsr => 1, cts => 1 });


$term = IO::Termios->new()

Construct a new IO::Termios object around the terminal for the program. This is found by checking if any of STDIN, STDOUT or STDERR are a terminal. The first one that's found is used. An error occurs if no terminal can be found by this method.

$term = IO::Termios->new( $handle )

Construct a new IO::Termios object around the given filehandle.

$term = IO::Termios->open( $path, $modestr )

Open the given path, and return a new IO::Termios object around the filehandle. If the open call fails, undef is returned.

If $modestr is provided, the constructor will pass it to the set_mode method before returning.


$attrs = $term->getattr

Makes a tcgetattr() call on the underlying filehandle, and returns a IO::Termios::Attrs object.

If the tcgetattr() call fails, undef is returned.

$term->setattr( $attrs )

Makes a tcsetattr() call on the underlying file handle, setting attributes from the given IO::Termios::Attrs object.

If the tcsetattr() call fails, undef is returned. Otherwise, a true value is returned.

$term->set_mode( $modestr )

$modestr = $term->get_mode

Accessor for the derived "mode string", which is a comma-joined concatenation of the baud rate, character size, parity mode, and stop size in a format such as


When setting the mode string, trailing components may be omitted meaning their value will not be affected.

$bits = $term->tiocmget

$term->tiocmset( $bits )

Accessor for the modem line control bits. Takes or returns a bitmask of values.

$term->tiombic( $bits )

$term->tiombis( $bits )

Bitwise mutator methods for the modem line control bits. tiombic will clear just the bits provided and leave the others unchanged; tiombis will set them.

$flags = $term->get_modem

Returns a hash reference containing named flags corresponding to the modem line control bits. Any bit that is set will yield a key in the returned hash of the same name. The bit names are

 dtr dsr rts cts cd ri

$term->set_modem( $flags )

Changes the modem line control bit flags as given by the hash reference. Each bit to be changed should be represented by a key in the $flags hash of the names given above. False values will be cleared, true values will be set. Other flags will not be altered.

$set = $term->getmodem_BIT

$term->setmodem_BIT( $set )

Accessor methods for each of the modem line control bits. A set of methods exists for each of the named modem control bits given above.


Theses methods are implemented in terms of the lower level methods, but provide an interface which is more abstract, and easier to re-implement on other non-POSIX systems. These should be used in preference to the lower ones.

For efficiency, when getting or setting a large number of flags, it may be more efficient to call getattr, then operate on the returned object, before possibly passing it to setattr. The returned IO::Termios::Attrs object supports the same methods as documented here.

The following two sections of code are therefore equivalent, though the latter is more efficient as it only calls setattr once.

 $term->setbaud( 38400 );
 $term->setcsize( 8 );
 $term->setparity( 'n' );
 $term->setstop( 1 );

 my $attrs = $term->getattr;
 $attrs->setbaud( 38400 );
 $attrs->setcsize( 8 );
 $attrs->setparity( 'n' );
 $attrs->setstop( 1 );
 $term->setattr( $attrs );

However, a convenient shortcut method is provided for the common case of setting the baud rate, character size, parity and stop size all at the same time. This is set_mode:

 $term->set_mode( "38400,8,n,1" );

$baud = $term->getibaud

$baud = $term->getobaud

$term->setibaud( $baud )

$term->setobaud( $baud )

$term->setbaud( $baud )

Convenience accessors for the ispeed and ospeed. $baud is an integer directly giving the line rate, instead of one of the Bnnn constants.

$bits = $term->getcsize

$term->setcsize( $bits )

Convenience accessor for the CSIZE bits of c_cflag. $bits is an integer 5 to 8.

$parity = $term->getparity

$term->setparity( $parity )

Convenience accessor for the PARENB and PARODD bits of c_cflag. $parity is n, o or e.

$stop = $term->getstop

$term->setstop( $stop )

Convenience accessor for the CSTOPB bit of c_cflag. $stop is 1 or 2.

$mode = $term->getflag_cread

$term->setflag_cread( $mode )

Accessor for the CREAD bit of the c_cflag. This enables the receiver.

$mode = $term->getflag_hupcl

$term->setflag_hupcl( $mode )

Accessor for the HUPCL bit of the c_cflag. This lowers the modem control lines after the last process closes the device.

$mode = $term->getflag_clocal

$term->setflag_clocal( $mode )

Accessor for the CLOCAL bit of the c_cflag. This controls whether local mode is enabled; which if set, ignores modem control lines.

$mode = $term->getflag_icanon

$term->setflag_icanon( $mode )

Accessor for the ICANON bit of c_lflag. This is called "canonical" mode and controls whether the terminal's line-editing feature will be used to return a whole line (if false), or if individual bytes from keystrokes will be returned as they are available (if true).

$mode = $term->getflag_echo

$term->setflag_echo( $mode )

Accessor for the ECHO bit of c_lflag. This controls whether input characters are echoed back to the terminal.


  • Adding more getflag_*/setflag_* convenience wrappers

  • Automatically upgrading STDIN/STDOUT/STDERR if appropriate, given a flag.

     use IO::Termios -upgrade;
     STDIN->setflag_echo( 0 );


  • IO::Tty - Import Tty control constants


Paul Evans <>