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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 });


If you pass the -upgrade option at import time, any of STDIN, STDOUT or STDERR that are found to be TTY wrappers are automatically upgraded into IO::Termios instances.

   use IO::Termios -upgrade;


Arbitrary Baud Rates on Linux

Linux supports a non-POSIX extension to the usual termios interface, which allows arbitrary baud rates to be set. IO::Termios can automatically make use of this ability if the Linux::Termios2 module is installed. If so, this will be used automatically and transparently, to allow the set*baud methods to set any rate allowed by the kernel/driver. If not, then only the POSIX-compatible rates may be used.



   $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.

new (handle)

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

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


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

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.

If $flags is provided, it will be passed on to the underlying sysopen() call used to open the filehandle. It should contain a bitwise-or combination of O_* flags from the Fcntl module - for example O_NOCTTY or O_NDELAY. The value O_RDWR will be added to this; the caller does not need to specify it directly. For example:

   use Fcntl qw( O_NOCTTY O_NDELAY );

   $term = IO::Termios->open( "/dev/ttyS0", O_NOCTTY|O_NDELAY );
   $term->setflag_clocal( 1 );
   $term->blocking( 1 );



   $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->tiocmbic( $bits );

   $term->tiocmbis( $bits );

Bitwise mutator methods for the modem line control bits. tiocmbic will clear just the bits provided and leave the others unchanged; tiocmbis 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.



Since version 0.07.

Adjusts several bit flags to put the terminal into a "raw" mode. Input is available a character at a time, echo is disabled, and all special processing of input and output characters is disabled.



   $mode = $term->getflag_FLAG;

   $term->setflag_FLAG( $mode );

Accessors for various control flags. The following methods are defined for specific flags:


Since version 0.09.

The INLCR bit of the c_iflag. This translates NL to CR on input.


Since version 0.09.

The IGNCR bit of the c_iflag. This ignores incoming CR characters.


Since version 0.09.

The ICRNL bit of the c_iflag. This translates CR to NL on input, unless IGNCR is also set.


Since version 0.09.

The IGNBRK bit of the c_iflag. This controls whether incoming break conditions are ignored entirely.


Since version 0.09.

The BRKINT bit of the c_iflag. This controls whether non-ignored incoming break conditions result in a SIGINT signal being delivered to the process. If not, such a condition reads as a nul byte.


Since version 0.09.

The PARMRK bit of the c_iflag. This controls how parity errors and break conditions are handled.


Since version 0.07.

The OPOST bit of the c_oflag. This enables system-specific post-processing on output.


The CREAD bit of the c_cflag. This enables the receiver.


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


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


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 true), or if individual bytes from keystrokes will be returned as they are available (if false).


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


   $term->setflags( @flags );

Since version 0.09.

A convenient wrapper to calling multiple flag setting methods in a sequence.

Each flag is specified by name, in lower case, prefixed by either a + symbol to enable it, or - to disable. For example:

   $term->setflags( "+igncr", "+opost", "+clocal", "-echo" );


  • Adding more getflag_*/setflag_* convenience wrappers


  • IO::Tty - Import Tty control constants


Paul Evans <>