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Manual Reference Pages  -  GRAPHICS::GNUPLOTIF (3)

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Graphics::GnuplotIF - A dynamic Perl interface to gnuplot



This documentation refers to Graphics::GnuplotIF version 1.6


  use Graphics::GnuplotIF qw(GnuplotIF);

  my  @x  = ( -2, -1.50, -1, -0.50,  0,  0.50,  1, 1.50, 2 ); # x values
  my  @y1 = (  4,  2.25,  1,  0.25,  0,  0.25,  1, 2.25, 4 ); # function 1
  my  @y2 = (  2,  0.25, -1, -1.75, -2, -1.75, -1, 0.25, 2 ); # function 2

  my  $plot1 = Graphics::GnuplotIF->new(title => "line", style => "points");

  $plot1->gnuplot_plot_y( \@x );                # plot 9 points over 0..8

  $plot1->gnuplot_pause( );                     # hit RETURN to continue

  $plot1->gnuplot_set_title( "parabola" );      # new title
  $plot1->gnuplot_set_style( "lines" );         # new line style

  $plot1->gnuplot_plot_xy( \@x, \@y1, \@y2 );   # plot 1: y1, y2 over x
  $plot1->gnuplot_plot_many( \@x, \@y1, \@x, \@y2 ); # plot 1: y1 - x, y2 - x

  my  $plot2  = Graphics::GnuplotIF->new;       # new plot object

  $plot2->gnuplot_set_xrange(  0, 4 );          # set x range
  $plot2->gnuplot_set_yrange( -2, 2 );          # set y range
  $plot2->gnuplot_cmd( "set grid" );            # send a gnuplot command
  $plot2->gnuplot_plot_equation(                # 3 equations in one plot
    "y1(x) = sin(x)",
    "y2(x) = cos(x)",
    "y3(x) = sin(x)/x" );

  $plot2->gnuplot_pause( );                     # hit RETURN to continue

  $plot2->gnuplot_plot_equation(                # rewrite plot 2
    "y4(x) = 2*exp(-x)*sin(4*x)" );

  $plot2->gnuplot_pause( );                     # hit RETURN to continue

  my  $plot3  = GnuplotIF;                      # new plot object

  my    @xyz    = (                             # 2-D-matrix, z-values
    [0,  1,  4,  9],
    [1,  2,  6, 15],
    [4,  6, 12, 27],
    [9, 15, 27, 54],

  $plot3->gnuplot_cmd( "set grid" );            # send a gnuplot command
  $plot3->gnuplot_set_plot_titles("surface");   # set legend
  $plot3->gnuplot_plot_3d( \@xyz );             # start 3-D-plot
  $plot3->gnuplot_pause( );                     # hit RETURN to continue


Graphics::GnuplotIF is a simple and easy to use dynamic Perl interface to <B>gnuplotB>. <B>gnuplotB> is a freely available, command-driven graphical display tool for Unix. It compiles and works quite well on a number of Unix flavours as well as other operating systems, including Windows with gnuplot.exe.

This module enables sending display requests asynchronously to <B>gnuplotB> through simple Perl subroutine calls.

A gnuplot session is an instance of class Graphics::GnuplotIF. The constructor starts <B>gnuplotB> as a separate process for each session. The plot commands are send through a pipe. The graphical output from <B>gnuplotB> will be displayed immediately.

Several independent plots can be started from one script. Each plot has its own pipe. All pipes will be closed automatically by the destructor when the script terminates. The <B>gnuplotB> processes terminate when the corresponding pipes are closed. Their graphical output will now disappear (but see parameter persist).

Graphics::GnuplotIF is similar to gnuplot_i , a C interface to <B>gnuplotB> ( ), and to gnuplot_i++ , a C++ interface to gnuplot ( ).


An object of this class represents an interface to a running <B>gnuplotB> process. During the creation of an object such an process will be started for each such object. Communication is done through an unidirectional pipe; the resulting stream is write-only.

Most methods return a reference to the Graphics::GnuplotIF object, allowing method calls to be chained like so:

  $plot1 -> gnuplot_plot_xy(\@x, \@y)
     -> gnuplot_reset;

The exception to this are gnuplot_get_plotnumber and gnuplot_get_object_id, which are used to obtain specific scalar values.


The constructor creates a new <B>gnuplotB> session object, referenced by a handle:

  $plot1  = Graphics::GnuplotIF->new( );

A few named arguments can be passed as key - value pairs (here shown with their default values):

  program      => gnuplot # fully qualified name of the Gnuplot executable
  style        => lines,  # one of the gnuplot line styles (see below)
  title        => ,       # string
  xlabel       => x,      # string
  ylabel       => y,      # string
  xrange       => [],       # array reference; autoscaling, if empty
  xrange       => [],       # array reference; autoscaling, if empty
  plot_titles  => [],       # array of strings; titles used in the legend
  scriptfile   => ,       # write all plot commands to the specified file
  plot_also    => 0,        # write all plot commands to the specified file,
                            # in addition show the plots
  persist      => 0,        # let plot windows survive after gnuplot exits
                            # 0 : close / 1 : survive
  objectname   => ,       # an optional name for the object
  silent_pause => 1,        # 0 suppress message from gnuplot_pause()
  no_error_log => 0,        # suppress ".gnuplot.${$}.${object_number}.stderr.log" file

These attributes are stored in each object.

Allowed line styles are

  boxes     dots   filledcurves  fsteps  histeps
  impulses  lines  linespoints   points  steps

The generated <B>gnuplotB> commands can be stored to a file instead of beeing executed immediately. This file can be used as input to <B>gnuplotB>, e.g.

  gnuplot < function_set_1.gnuplot

A script file can also be used for checking the commands send to <B>gnuplotB>.

The objects are automatically deleted by a destructor. The destructor closes the pipe to the <B>gnuplotB> process belonging to that object. The <B>gnuplotB> process will also terminate and remove the graphic output. The termination can be controlled by the method gnuplot_pause .

The program argument is provided to allow Graphics::GnuplotIF to be used with Gnuplot on Windows using gnuplot.exe, a compilation which includes code that emulates a unix pipe.


The short form of the constructor above (new):

  use Graphics::GnuplotIF qw(GnuplotIF);

  $plot1  = GnuplotIF;

This subroutine is exported only on request.


  $plot1->gnuplot_plot_y( \@y1, \@y2 );

gnuplot_plot_y takes one or more array references and plots the values over the x-values 0, 1, 2, 3, ...


  $plot1->gnuplot_plot_xy( \@x, \@y1, \@y2 );

gnuplot_plot_xy takes two or more array references. The first array is assumed to contain the x-values for the following function values.


  %y1 = ( y_values => \@y1, style_spec => "lines lw 3" );
  %y2 = ( y_values => \@y2,
          style_spec => "points pointtype 4 pointsize 5" );

  $plot1->gnuplot_plot_xy_style( \@x, \%y1, \%y2 );

gnuplot_plot_xy_style takes one array reference and one or more hash references. The first array is assumed to contain the x-values for the following function values. The following hashes are assumed to contain pairs of y-values and individual style specifications for use in the plot command. The ’style_spec’ settings are placed between with and title of <B>gnuplotB>’s plot command.


  $plot1->gnuplot_plot_xy( \@x1, \@y1, \@x2, \@y2 );

gnuplot_plot_many takes pairs of array references. Each pair represents a function and is a reference to the arrays of x- and y-values for that function.


  %f1 = ( x_values => \@x1, y_values => \@y1,
          style_spec => "lines lw 3" );
  %f2 = ( x_values => \@x2, y_values => \@y2,
          style_spec => "points pointtype 4 pointsize 5" );

  $plot1->gnuplot_plot_many_style( \%f1, \%f2 );

gnuplot_plot_many_style takes one or more hash references. The hashes are assumed to contain array referenses to x-values and y-values and individual style specifications for use in the plot command. The ’style_spec’ settings are placed between with and title of <B>gnuplotB>’s plot command.


  $plot2->gnuplot_plot_equation(         # 3 equations in one plot
    "y1(x) = sin(x)",
    "y2(x) = cos(x)",
    "y3(x) = sin(x)/x" );

gnuplot_plot_equation takes one or more <B>gnuplotB> function descriptions as strings. The plot ranges can be controlled by gnuplot_set_xrange and gnuplot_set_yrange .


  $plot2->gnuplot_plot_3d( \@array );    # 3-D-plot

gnuplot_plot_3d takes one reference to an 2-D-array of z-values.


  $plot1->gnuplot_pause( [time] [,text] );

This is an emulation of the <B>gnuplotB> pause command. It displays any text associated with the command and waits a specified amount of time or until the carriage return is pressed. The message can be suppressed by

  silent_pause => 0

given to the constructor (see new ).

time may be any constant or expression. Choosing 0 (default) will wait until a carriage return is hit, a negative value won’t pause at all, and a positive number will wait the specified number of seconds.

The time value and the text are stored in the object and reused. A sequence like

  $plot1->gnuplot_plot_y( \@y1 );
  $plot1->gnuplot_pause( 5.5 );          # delay is 5.5 seconds

  $plot1->gnuplot_plot_y( \@y2 );
  $plot1->gnuplot_pause( );

  $plot1->gnuplot_plot_y( \@y3 );
  $plot1->gnuplot_pause( );

will display 3 plots with 5.5 seconds delay.


  $plot2->gnuplot_cmd( set grid,
                       set timestamp "%d/%m/%y %H:%M" 0,0 "Helvetica"

gnuplot_cmd can be used to send one or more <B>gnuplotB> commands, especially those not wrapped by a Graphics::GnuplotIF method.



Set all options set with the set command to their <B>gnuplotB> default values.


  $plot1->gnuplot_set_style( "steps" );   # new line style

Sets one of the allowed line styles (see new ) in a plot command.


  $plot1->gnuplot_set_title("parabola");  # new title

Sets the plot title. Equivalent to the <B>gnuplotB> command set title "parabola".


  $plot1->gnuplot_set_xlabel("time (days)");

Sets the x axis label. Equivalent to the <B>gnuplotB> command set xlabel "time (days)".


  $plot1->gnuplot_set_ylabel("bugs fixed");

Sets the y axis label. Equivalent to the <B>gnuplotB> command set ylabel "bugs fixed".


  $plot1->gnuplot_set_xrange( left, right );

Sets the horizontal range that will be displayed. Equivalent to the <B>gnuplotB> command set xrange [left:right].


  $plot1->gnuplot_set_yrange( low, high );

Sets the vertical range that will be displayed. Equivalent to the <B>gnuplotB> command set yrange [low:high].


  $plot1->gnuplot_set_plot_titles( @ytitles );

Sets the list of titles used in the key for each of the y-coordinate data sets specified in subsequent calls to gnuplot_plot_xy or gnuplot_plot_y commands. This is not equivalent to a complete <B>gnuplotB> command; rather it adds a title clause to each data set specified in a <B>gnuplotB> plot command.


gnuplot_cmd can be used to write a plot into a file or make a printable file by setting/resetting the terminal and the output file:

                            color lw 3 );

  $plot1->gnuplot_plot_xy( \@x, \@y1, \@y2 );


The 1. parameter is a file name, the 2. parameter is a <B>gnuplotB> terminal type, the 3. parameter is a string with additional terminal parameters (optional). The current terminal settings will be saved.


Restores the saved terminal settings after a call to gnuplot_hardcopy(). Output will go to STDOUT again.

Print a plot directly

A hardcopy can be made with an appropriate output format and a pipe to a printer:

  $plot1->gnuplot_cmd( set terminal postscript,
                       set output   " | lpr "  );

  $plot1->gnuplot_plot_xy( \@x, \@y1, \@y2 );

  $plot1->gnuplot_cmd( set output,
                       set terminal x11 );


Get the (internal) object number (and the object name):

   $obj_number              = $plot1->gnuplot_get_object_id();
  ($obj_number, $obj_name)  = $plot1->gnuplot_get_object_id();

The object number is set automatically by the constructor. The object name can be set by the constructor (objectname => ’MyName’).


Get the (internal) plot number of the <B>nextB> plot:

   $plot_number             = $plot1->gnuplot_get_plotnumber()

The plot number is set automatically by the constructor starting with 1. Each call to


increments this number by 1. This can be used to identify single plots, e.g. with

  $plot->gnuplot_cmd( "set timestamp \"plot number ${plot_number} / %c\"" );


<B>GnuplotIFB> constructor, short form (see GnuplotIF ).


Dialog messages and diagnostic messages start with Graphics::GnuplotIF (object NR): ... .

NR is the number of the corresponding Graphics::GnuplotIF object and output stream. NR counts the objects in the order of their generation.

The gnuplot messages going to STDERR will be redirected to the file .gnuplot.PPP.OOO.stderr.log. PPP is the process number, OOO is the number of the plot object (see gnuplot_get_object_id).


The environment variable DISPLAY is checked for the display.


o gnuplot ( ) must be installed.

Using Graphics::GnuplotIF on Windows requires having the gnuplot.exe version installed. This is the version that emulates a pipe. The Graphics::GnuplotIF object must then be instantiated with the program argument, like so:

  my $plot = Graphics::GnuplotIF -> new(program => C:\gnuplot\binaries\gnuplot.exe);

A recent compilation of Gnuplot for Windows can be found at SourceForge: <>.

o The module Carp is used for error handling.
o The module IO::Handle is used to handle output pipes. Your operating system must support pipes, of course.


There are no known incompatibilities.


  $plot1->gnuplot_cmd("pause -1");     # send the gnuplot pause command

does not work. Use

  $plot1->gnuplot_pause( );

There are no known bugs in this module. Please report problems to author. Patches are welcome.


Dr.-Ing. Fritz Mehner (


Stephen Marshall (smarshall at wsi dot com) contributed gnuplot_set_plot_titles.

Georg Bauhaus (bauhaus at futureapps dot de) contributed gnuplot_plot_xy_style.

Bruce Ravel (bravel at bnl dot gov) contributed gnuplot_plot_many and gnuplot_plot_many_style, made method calls chainable, and added Windows support.


Copyright (C) 2005-2011 by Fritz Mehner

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perldoc perlartistic. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


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