=head1 TALK

I just gave a talk about this at L<SCaLE
17x|https://www.socallinuxexpo.org/scale/17x>. Presentation lives
L<here|https://github.com/dkogan/talk-feedgnuplot-vnlog/blob/master/feedgnuplot-vnlog.org>.

=head1 NAME

feedgnuplot - General purpose pipe-oriented plotting tool

=head1 SYNOPSIS

Simple plotting of piped data:

 $ seq 5 | awk '{print 2*$1, $1*$1}'
 2 1
 4 4
 6 9
 8 16
 10 25

 $ seq 5 | awk '{print 2*$1, $1*$1}' |
   feedgnuplot --lines --points --legend 0 "data 0" --title "Test plot" --y2 1
               --unset grid --terminal 'dumb 80,40' --exit

                                  Test plot

  10 +-----------------------------------------------------------------+ 25
     |       +        +       +       +       +        +       +    *##|
     |                                                  data 0 ***A*#* |
     |                                                          ** #   |
   9 |-+                                                      ** ##    |
     |                                                      **  #      |
     |                                                    **   #       |
     |                                                  **   ##      +-| 20
   8 |-+                                               A    #          |
     |                                               **    #           |
     |                                             **    ##            |
     |                                           **     #              |
     |                                         **      B               |
   7 |-+                                     **      ##                |
     |                                     **      ##                +-| 15
     |                                   **       #                    |
     |                                 **       ##                     |
   6 |-+                             *A       ##                       |
     |                             **       ##                         |
     |                           **        #                           |
     |                         **        ##                          +-| 10
   5 |-+                     **        ##                              |
     |                     **        #B                                |
     |                   **        ##                                  |
     |                 **        ##                                    |
   4 |-+              A       ###                                      |
     |              **      ##                                         |
     |            **      ##                                         +-| 5
     |          **      ##                                             |
     |        **    ##B#                                               |
   3 |-+    **  ####                                                   |
     |    **####                                                       |
     |  ####                                                           |
     |##     +        +       +       +       +        +       +       |
   2 +-----------------------------------------------------------------+ 0
     1      1.5       2      2.5      3      3.5       4      4.5      5


Simple real-time plotting example: plot how much data is received on the wlan0
network interface in bytes/second (uses bash, awk and Linux):

 $ while true; do sleep 1; cat /proc/net/dev; done |
   gawk '/wlan0/ {if(b) {print $2-b; fflush()} b=$2}' |
   feedgnuplot --lines --stream --xlen 10 --ylabel 'Bytes/sec' --xlabel seconds

=head1 DESCRIPTION

This is a flexible, command-line-oriented frontend to Gnuplot. It creates
plots from data coming in on STDIN or given in a filename passed on the
commandline. Various data representations are supported, as is hardcopy
output and streaming display of live data. A simple example:

 $ seq 5 | awk '{print 2*$1, $1*$1}' | feedgnuplot

You should see a plot with two curves. The C<awk> command generates some data to
plot and the C<feedgnuplot> reads it in from STDIN and generates the plot. The
C<awk> invocation is just an example; more interesting things would be plotted
in normal usage. No commandline-options are required for the most basic
plotting. Input parsing is flexible; every line need not have the same number of
points. New curves will be created as needed.

The most commonly used functionality of gnuplot is supported directly by the
script. Anything not directly supported can still be done with options such as
C<--set>, C<--extracmds> C<--style>, etc. Arbitrary gnuplot commands can be
passed in with C<--extracmds>. For example, to turn off the grid, you can pass
in C<--extracmds 'unset grid'>. Commands C<--set> and C<--unset> exists to
provide nicer syntax, so this is equivalent to passing C<--unset grid>. As many
of these options as needed can be passed in. To add arbitrary curve styles, use
C<--style curveID extrastyle>. Pass these more than once to affect more than one
curve.

To apply an extra style to I<all> the curves that lack an explicit C<--style>,
pass in C<--styleall extrastyle>. In the most common case, the extra style is
C<with something>. To support this more simply, you can pass in C<--with
something> instead of C<--styleall 'with something'>. C<--styleall> and
C<--with> are mutually exclusive. Furthermore any curve-specific C<--style>
overrides the global C<--styleall> or C<--with> setting.

=head2 Data formats

By default, each value present in the incoming data represents a distinct data
point, as demonstrated in the original example above (we had 10 numbers in the
input and 10 points in the plot). If requested, the script supports more
sophisticated interpretation of input data

=head3 Domain selection

If C<--domain> is passed in, the first value on each line of input is
interpreted as the I<X>-value for the rest of the data on that line. Without
C<--domain> the I<X>-value is the line number, and the first value on a line is
a plain data point like the others. Default is C<--nodomain>. Thus the original
example above produces 2 curves, with B<1,2,3,4,5> as the I<X>-values. If we run
the same command with C<--domain>:

 $ seq 5 | awk '{print 2*$1, $1*$1}' | feedgnuplot --domain

we get only 1 curve, with B<2,4,6,8,10> as the I<X>-values. As many points as
desired can appear on a single line, but all points on a line are associated
with the I<X>-value at the start of that line.

=head3 Curve indexing

We index the curves in one of 3 ways: sequentially, explicitly with a
C<--dataid> or by C<--vnlog> headers.

By default, each column represents a separate curve. The first column (after any
domain) is curve C<0>. The next one is curve C<1> and so on. This is fine unless
sparse data is to be plotted. With the C<--dataid> option, each point is
represented by 2 values: a string identifying the curve, and the value itself.
If we add C<--dataid> to the original example:

 $ seq 5 | awk '{print 2*$1, $1*$1}' | feedgnuplot --dataid --autolegend

we get 5 different curves with one point in each. The first column, as produced
by C<awk>, is B<2,4,6,8,10>. These are interpreted as the IDs of the curves to
be plotted.

If we're plotting C<vnlog> data (L<https://www.github.com/dkogan/vnlog>) then we
can get the curve IDs from the vnlog header. Vnlog is a trivial data format
where lines starting with C<#> are comments and the first comment contains
column labels. If we have such data, C<feedgnuplot --vnlog> can interpret these
column labels if the C<vnlog> perl modules are available.

The C<--autolegend> option adds a legend using the given IDs to
label the curves. The IDs need not be numbers; generic strings are accepted. As
many points as desired can appear on a single line. C<--domain> can be used in
conjunction with C<--dataid> or C<--vnlog>.

=head3 Multi-value style support

Depending on how gnuplot is plotting the data, more than one value may be needed
to represent the range of a single point. Basic 2D plots have 2 numbers
representing each point: 1 domain and 1 range. But if plotting with
C<--circles>, for instance, then there's an extra range value: the radius. Many
other gnuplot styles require more data: errorbars, variable colors (C<with
points palette>), variable sizes (C<with points ps variable>), labels and so on.
The feedgnuplot tool itself does not know about all these intricacies, but they
can still be used, by specifying the specific style with C<--style>, and
specifying how many values are needed for each point with any of
C<--rangesizeall>, C<--tuplesizeall>, C<--rangesize>, C<--tuplesize>. These
options are required I<only> for styles not explicitly supported by feedgnuplot;
supported styles do the right thing automatically.

Specific example: if making a 2d plot of y error bars, the exact format can be
queried by running C<gnuplot> and invoking C<help yerrorbars>. This tells us
that there's a 3-column form: C<x y ydelta> and a 4-column form: C<x y ylow
yhigh>. With 2d plots feedgnuplot will always output the 1-value domain C<x>, so
the rangesize is 2 and 3 respectively. Thus the following are equivalent:

 $ echo '1 2 0.3
         2 3 0.4
         3 4 0.5' | feedgnuplot --domain --rangesizeall 2 --with 'yerrorbars'

 $ echo '1 2 0.3
         2 3 0.4
         3 4 0.5' | feedgnuplot --domain --tuplesizeall 3 --with 'yerrorbars'

 $ echo '1 2 1.7 2.3
         2 3 2.6 3.4
         3 4 3.5 4.5' | feedgnuplot --domain --rangesizeall 3 --with 'yerrorbars'

=head3 3D data

To plot 3D data, pass in C<--3d>. C<--domain> MUST be given when plotting 3D
data to avoid domain ambiguity. If 3D data is being plotted, there are by
definition 2 domain values instead of one (I<Z> as a function of I<X> and I<Y>
instead of I<Y> as a function of I<X>). Thus the first 2 values on each line are
interpreted as the domain instead of just 1. The rest of the processing happens
the same way as before.

=head3 Time/date data

If the input data domain is a time/date, this can be interpreted with
C<--timefmt>. This option takes a single argument: the format to use to parse
the data. The format is documented in 'set timefmt' in gnuplot, although the
common flags that C<strftime> understands are generally supported. The backslash
sequences in the format are I<not> supported, so if you want a tab, put in a tab
instead of \t. Whitespace in the format I<is> supported. When this flag is
given, some other options act a little bit differently:

=over

=item

C<--xlen> is an I<integer> in seconds

=item

C<--xmin> and C<--xmax> I<must> use the format passed in to C<--timefmt>

=back

Using this option changes both the way the input is parsed I<and> the way the
x-axis tics are labelled. Gnuplot tries to be intelligent in this labelling, but
it doesn't always do what the user wants. The labelling can be controlled with
the gnuplot C<set format> command, which takes the same type of format string as
C<--timefmt>. Example:

 $ sar 1 -1 |
   awk '$1 ~ /..:..:../ && $8 ~/^[0-9\.]*$/ {print $1,$8; fflush()}' |
   feedgnuplot --stream --domain
                --lines --timefmt '%H:%M:%S'
                --set 'format x "%H:%M:%S"'

This plots the 'idle' CPU consumption against time.

Note that while gnuplot supports the time/date on any axis, I<feedgnuplot>
currently supports it I<only> as the x-axis domain. This may change in the
future.

=head2 Real-time streaming data

To plot real-time data, pass in the C<--stream [refreshperiod]> option. Data
will then be plotted as it is received. The plot will be updated every
C<refreshperiod> seconds. If the period isn't specified, a 1Hz refresh rate is
used. To refresh at specific intervals indicated by the data, set the
refreshperiod to 0 or to 'trigger'. The plot will then I<only> be refreshed when
a data line 'replot' is received. This 'replot' command works in both triggered
and timed modes, but in triggered mode, it's the only way to replot. Look in
L</"Special data commands"> for more information.

To plot only the most recent data (instead of I<all> the data), C<--xlen
windowsize> can be given. This will create an constantly-updating, scrolling
view of the recent past. C<windowsize> should be replaced by the desired length
of the domain window to plot, in domain units (passed-in values if C<--domain>
or line numbers otherwise). If the domain is a time/date via C<--timefmt>, then
C<windowsize> is and I<integer> in seconds. If we're plotting a histogram, then
C<--xlen> causes a histogram over a moving window to be computed. The subtlely
here is that with a histogram you don't actually I<see> the domain since only
the range is analyzed. But the domain is still there, and can be utilized with
C<--xlen>. With C<--xlen> we can plot I<only> histograms or I<only>
I<non>-histograms.

=head3 Special data commands

If we are reading streaming data, the input stream can contain special commands
in addition to the raw data. Feedgnuplot looks for these at the start of every
input line. If a command is detected, the rest of the line is discarded. These
commands are

=over

=item C<replot>

This command refreshes the plot right now, instead of waiting for the next
refresh time indicated by the timer. This command works in addition to the timed
refresh, as indicated by C<--stream [refreshperiod]>.

=item C<clear>

This command clears out the current data in the plot. The plotting process
continues, however, to any data following the C<clear>.

=item C<exit>

This command causes feedgnuplot to exit.

=back

=head2 Hardcopy output

The script is able to produce hardcopy output with C<--hardcopy outputfile>. The
output type can be inferred from the filename, if B<.ps>, B<.eps>, B<.pdf>,
B<.svg>, B<.png> or B<.gp> is requested. If any other file type is requested,
C<--terminal> I<must> be passed in to tell gnuplot how to make the plot. If
C<--terminal> is passed in, then the C<--hardcopy> argument only provides the
output filename.

The B<.gp> output is special. Instead of asking gnuplot to plot to a particular
terminal, writing to a B<.gp> simply dumps a self-executable gnuplot script into
the given file. This is similar to what C<--dump> does, but writes to a file,
and makes sure that the file can be self-executing.

=head2 Self-plotting data files

This script can be used to enable self-plotting data files. There are several
ways of doing this: with a shebang (#!) or with inline perl data.

=head3 Self-plotting data with a #!

A self-plotting, executable data file C<data> is formatted as

 $ cat data
 #!/usr/bin/feedgnuplot --lines --points
 2 1
 4 4
 6 9
 8 16
 10 25
 12 36
 14 49
 16 64
 18 81
 20 100
 22 121
 24 144
 26 169
 28 196
 30 225

This is the shebang (#!) line followed by the data, formatted as before. The
data file can be plotted simply with

 $ ./data

The caveats here are that on Linux the whole #! line is limited to 127
characters and that the full path to feedgnuplot must be given. The 127
character limit is a serious limitation, but this can likely be resolved with a
kernel patch. I have only tried on Linux 2.6.

=head3 Self-plotting data with gnuplot

Running C<feedgnuplot --hardcopy plotdata.gp ....> will create a self-executable
gnuplot script in C<plotdata.gp>

=head3 Self-plotting data with perl inline data

Perl supports storing data and code in the same file. This can also be used to
create self-plotting files:

 $ cat plotdata.pl
 #!/usr/bin/perl
 use strict;
 use warnings;

 open PLOT, "| feedgnuplot --lines --points" or die "Couldn't open plotting pipe";
 while( <DATA> )
 {
   my @xy = split;
   print PLOT "@xy\n";
 }
 __DATA__
 2 1
 4 4
 6 9
 8 16
 10 25
 12 36
 14 49
 16 64
 18 81
 20 100
 22 121
 24 144
 26 169
 28 196
 30 225

This is especially useful if the logged data is not in a format directly
supported by feedgnuplot. Raw data can be stored after the __DATA__ directive,
with a small perl script to manipulate the data into a useable format and send
it to the plotter.

=head1 ARGUMENTS

=over

=item

--C<[no]domain>

If enabled, the first element of each line is the domain variable. If not, the
point index is used

=item

--C<[no]dataid>

If enabled, each data point is preceded by the ID of the data set that point
corresponds to. This ID is interpreted as a string, NOT as just a number. If not
enabled, the order of the point is used.

As an example, if line 3 of the input is "0 9 1 20" then

=over

=item

C<--nodomain --nodataid> would parse the 4 numbers as points in 4 different
curves at x=3

=item

C<--domain --nodataid> would parse the 4 numbers as points in 3 different
curves at x=0. Here, 0 is the x-variable and 9,1,20 are the data values

=item

C<--nodomain --dataid> would parse the 4 numbers as points in 2 different
curves at x=3. Here 0 and 1 are the data IDs and 9 and 20 are the
data values

=item

C<--domain --dataid> would parse the 4 numbers as a single point at
x=0. Here 9 is the data ID and 1 is the data value. 20 is an extra
value, so it is ignored. If another value followed 20, we'd get another
point in curve ID 20

=back

=item

C<--vnlog>

Vnlog is a trivial data format where lines starting with C<#> are comments and
the first comment contains column labels. Some tools for working with such data
are available from the C<vnlog> project: L<https://www.github.com/dkogan/vnlog>.
With the C<vnlog> perl modules installed, we can read the vnlog column headers
with C<feedgnuplot --vnlog>. This replaces C<--dataid>, and we can do all the
normal things with these headers. For instance C<feedgnuplot --vnlog
--autolegend> will generate plot legends for each column in the vnlog, using the
vnlog column label in the legend.

=item

C<--[no]3d>

Do [not] plot in 3D. This only makes sense with C<--domain>. Each domain here is
an (x,y) tuple

=item

--C<timefmt [format]>

Interpret the X data as a time/date, parsed with the given format

=item

C<--colormap>

Show a colormapped xy plot. Requires extra data for the color. zmin/zmax can be
used to set the extents of the colors. Automatically sets the
C<--rangesize>/C<--tuplesize>.

=item

C<--stream [period]>

Plot the data as it comes in, in realtime. If period is given, replot every
period seconds. If no period is given, replot at 1Hz. If the period is given as
0 or 'trigger', replot I<only> when the incoming data dictates this. See the
L</"Real-time streaming data"> section of the man page.

=item

C<--[no]lines>

Do [not] draw lines to connect consecutive points

=item

C<--[no]points>

Do [not] draw points

=item

C<--circles>

Plot with circles. This requires a radius be specified for each point.
Automatically sets the C<--rangesize>/C<--tuplesize>. C<Not> supported for 3d
plots.

=item

C<--title xxx>

Set the title of the plot

=item

C<--legend curveID legend>

Set the label for a curve plot. Use this option multiple times for multiple
curves. With C<--dataid>, curveID is the ID. Otherwise, it's the index of the
curve, starting at 0

=item

C<--autolegend>

Use the curve IDs for the legend. Titles given with C<--legend> override these

=item

C<--xlen xxx>

When using C<--stream>, sets the size of the x-window to plot. Omit this or set
it to 0 to plot ALL the data. Does not make sense with 3d plots. Implies
C<--monotonic>. If we're plotting a histogram, then C<--xlen> causes a histogram
over a moving window to be computed. The subtlely here is that with a histogram
you don't actually I<see> the domain since only the range is analyzed. But the
domain is still there, and can be utilized with C<--xlen>. With C<--xlen> we can
plot I<only> histograms or I<only> I<non>-histograms.


=item

C<--xmin/xmax/ymin/ymax/y2min/y2max/zmin/zmax xxx>

Set the range for the given axis. These x-axis bounds are ignored in a streaming
plot. The y2-axis bound do not apply in 3d plots. The z-axis bounds apply
I<only> to 3d plots or colormaps. Note that there is no C<--xrange> to set both
sides at once or C<--xinv> to flip the axis around: anything more than the
basics supported in this option is clearly obtainable by talking to gnuplot, for
instance C<--set 'xrange [20:10]'> to set the given inverted bounds.

=item

C<--xlabel/ylabel/y2label/zlabel xxx>

Label the given axis. The y2-axis label does not apply to 3d plots while the
z-axis label applies I<only> to 3d plots.

=item

C<--y2 xxx>

Plot the data specified by this curve ID on the y2 axis. Without C<--dataid>,
the ID is just an ordered 0-based index. Does not apply to 3d plots. Can be
passed multiple times, or passed a comma-separated list. By default the y2-axis
curves look the same as the y-axis ones. I.e. the viewer of the resulting plot
has to be told which is which via an axes label, legend, etc. Prior to version
1.25 of feedgnuplot the curves plotted on the y2 axis were drawn with a thicker
line. This is no longer the case, but that behavior can be brought back by
passing something like

 --y2 curveid --style curveid 'linewidth 3'

=item

C<--histogram curveID>

Set up a this specific curve to plot a histogram. The bin width is given with
the C<--binwidth> option (assumed 1.0 if omitted). If a drawing style is not
specified for this curve (C<--curvestyle>) or all curves (C<--with>,
C<--curvestyleall>) then the default histogram style is set: filled boxes with
borders. This is what the user generally wants. This works with C<--domain>
and/or C<--stream>, but in those cases the x-value is used I<only> to cull old
data because of C<--xlen> or C<--monotonic>. I.e. the domain values are I<not>
drawn in any way. Can be passed multiple times, or passed a comma- separated
list

=item

C<--binwidth width>

The width of bins when making histograms. This setting applies to ALL histograms
in the plot. Defaults to 1.0 if not given.

=item

C<--histstyle style>

Normally, histograms are generated with the 'smooth frequency' gnuplot style.
C<--histstyle> can be used to select different C<smooth> settings (see the
gnuplot C<help smooth> page for more info). Allowed values are 'frequency' (the
default), 'fnormal' (available in very recent gnuplots), 'unique', 'cumulative'
and 'cnormal'. 'fnormal' is a normalized histogram. 'unique' indicates whether a
bin has at least one item in it: instead of counting the items, it'll always
report 0 or 1. 'cumulative' is the integral of the 'frequency' histogram.
'cnormal' is like 'cumulative', but rescaled to end up at 1.0.

=item

C<--style curveID style>

Additional styles per curve. With C<--dataid>, curveID is the ID. Otherwise,
it's the index of the curve, starting at 0. curveID can be a comma-separated
list of IDs to which the given style should apply. Use this option multiple
times for multiple curves. C<--styleall> does I<not> apply to curves that have a
C<--style>.

=item

C<--curvestyle curveID>

Synonym for C<--style>

=item

C<--styleall xxx>

Additional styles for all curves that have no C<--style>. This is overridden by
any applicable C<--style>. Exclusive with C<--with>.

=item

C<--curvestyleall xxx>

Synonym for C<--styleall>

=item

C<--with xxx>

Same as C<--styleall>, but prefixed with "with". Thus

 --with boxes

is equivalent to

 --styleall 'with boxes'

Exclusive with C<--styleall>.

=item

C<--extracmds xxx>

Additional commands to pass on to gnuplot verbatim. These could contain extra
global styles for instance. Can be passed multiple times.

=item

C<--set xxx>

Additional 'set' commands to pass on to gnuplot verbatim. C<--set 'a b c'> will
result in gnuplot seeing a C<set a b c> command. Can be passed multiple times.

=item

C<--unset xxx>

Additional 'unset' commands to pass on to gnuplot verbatim. C<--unset 'a b c'>
will result in gnuplot seeing a C<unset a b c> command. Can be passed multiple
times.

=item

C<--image filename>

Overlays the data on top of a raster image given in C<filename>. This is passed
through to gnuplot via C<--equation>, and is not interpreted by C<feedgnuplot>
other than checking for existence. Usually images have their origin at the
top-left corner, while plots have it in the bottom-left corner instead. Thus if
the y-axis extents are not specified (C<--ymin>, C<--ymax>, C<--set 'yrange
...'>) this option will also flip around the y axis to make the image appear
properly. Since this option is just a passthrough to gnuplot, finer control can
be achieved by passing in C<--equation> and C<--set yrange ...> directly.

C<--equation xxx>

Gnuplot can plot both data and symbolic equations. C<feedgnuplot> generally
plots data, but with this option can plot symbolic equations I<also>. This is
generally intended to augment data plots, since for equation-only plots you
don't need C<feedgnuplot>. C<--equation> can be passed multiple times for
multiple equations. The given strings are passed to gnuplot directly without
anything added or removed, so styling and such should be applied in the string.
A basic example:

 seq 100 | awk '{print $1/10, $1/100}' |
   feedgnuplot --with 'lines lw 3' --domain --ymax 1
               --equation 'sin(x)/x' --equation 'cos(x)/x with lines lw 4'

Here I plot the incoming data (points along a line) with the given style (a line
with thickness 3), I<and> I plot two damped sinusoids on the same plot. The
sinusoids are not affected by C<feedgnuplot> styling, so their styles are set
separately, as in this example. More complicated example:

 seq 360 | perl -nE '$th=$_/360 * 3.14*2; $c=cos($th); $s=sin($th); say "$c $s"' |
   feedgnuplot --domain --square
               --set parametric --set "trange [0:2*3.14]" --equation "sin(t),cos(t)"

Here the data I generate is points along the unit circle. I plot these as
points, and I I<also> plot a true circle as a parametric equation.

=item

C<--square>

Plot data with aspect ratio 1. For 3D plots, this controls the aspect ratio for
all 3 axes

=item

C<--square-xy>

For 3D plots, set square aspect ratio for ONLY the x,y axes

=item

C<--hardcopy xxx>

If not streaming, output to a file specified here. Format inferred from
filename, unless specified by C<--terminal>. If C<--terminal> is given,
C<--hardcopy> sets I<only> the output filename.

=item

C<--terminal xxx>

String passed to 'set terminal'. No attempts are made to validate this.
C<--hardcopy> sets this to some sensible defaults if C<--hardcopy> is set to a
filename ending in C<.png>, C<.pdf>, C<.ps>, C<.eps> or C<.svg>. If any other
file type is desired, use both C<--hardcopy> and C<--terminal>

=item

C<--maxcurves N>

The maximum allowed number of curves. This is 100 by default, but can be reset
with this option. This exists purely to prevent perl from allocating all of the
system's memory when reading bogus data

=item

C<--monotonic>

If C<--domain> is given, checks to make sure that the x-coordinate in the input
data is monotonically increasing. If a given x-variable is in the past, all data
currently cached for this curve is purged. Without C<--monotonic>, all data is
kept. Does not make sense with 3d plots. No C<--monotonic> by default. The data
is replotted before being purged. This is useful in streaming plots where the
incoming data represents multiple iterations of the same process (repeated
simulations of the same period in time, for instance).

=item

C<--rangesize curveID N>

The options C<--rangesizeall> and C<--rangesize> set the number of values are
needed to represent each point being plotted (see L</"Multi-value style
support"> above). These options are I<only> needed if unknown styles are used,
with C<--styleall> or C<--with> for instance.

C<--rangesize> is used to set how many values are needed to represent the range
of a point for a particular curve. This overrides any defaults that may exist
for this curve only.

With C<--dataid>, curveID is the ID. Otherwise, it's the index of the curve,
starting at 0. curveID can be a comma-separated list of IDs to which the given
rangesize should apply.

=item

C<--tuplesize curveID N>

Very similar to C<--rangesize>, but instead of specifying the I<range> only,
this specifies the whole tuple. For instance if we're plotting circles, the
tuplesize is 3: C<x,y,radius>. In a 2D plot there's a 1-dimensional domain:
C<x>, so the rangesize is 2: C<y,radius>. This dimensionality can be given
either way.

=item

C<--rangesizeall N>

Like C<--rangesize>, but applies to I<all> the curves.

=item

C<--tuplesizeall N>

Like C<--tuplesize>, but applies to I<all> the curves.

=item

C<--dump>

Instead of printing to gnuplot, print to STDOUT. Very useful for debugging. It
is possible to send the output produced this way to gnuplot directly.

=item

C<--exit>

This controls what happens when the input data is exhausted, or when some part
of the C<feedgnuplot> pipeline is killed. This option does different things
depending on whether C<--stream> is active, so read this closely.

With interactive gnuplot terminals (qt, x11, wxt), the plot windows live in a
separate process from the main C<gnuplot> process. It is thus possible for the
main C<gnuplot> process to exit, while leaving the plot windows up (a caveat is
that such decapitated windows aren't interactive). There are 3 possible states
of the polotting pipeline:

=over

=item Alive: C<feedgnuplot>, C<gnuplot> alive, plot window process alive, no
shell prompt (shell busy with C<feedgnuplot>)

=item Half-alive: C<feedgnuplot>, C<gnuplot> dead, plot window process alive
(but non-interactive), shell prompt available

=item Dead: C<feedgnuplot>, C<gnuplot> dead, plot window process dead, shell
prompt available

=back

The possibilities are:

=over

=item No C<--stream>, all data read in

=over

=item no C<--exit> (default)

Alive. Need to Ctrl-C to get back into the shell

=item C<--exit>

Half-alive. Non-interactive prompt up, and the shell accepts new commands.
Without C<--stream> the goal is to show a plot, so a Dead state would not be
useful.

=back

=item C<--stream>, all data read in or the C<feedgnuplot> process terminated

=over

=item no C<--exit> (default)

Alive. Need to Ctrl-C to get back into the shell. This means that when making
live plots, the first Ctrl-C kills the data feeding process, but leaves the
final plot up for inspection. A second Ctrl-C kills feedgnuplot as well.

=item C<--exit>

Dead. No plot is shown, and the shell accepts new commands. With C<--stream> the
goal is to show a plot as the data comes in, which we have been doing. Now that
we're done, we can clean up everything.

=back

=back

Note that one usually invokes C<feedgnuplot> as a part of a shell pipeline:

 $ write_data | feedgnuplot

If the user terminates this pipeline with ^C, then I<all> the processes in the
pipeline receive SIGINT. This normally kills C<feedgnuplot> and all its
C<gnuplot> children, and we let this happen unless C<--stream> and no C<--exit>.
If C<--stream> and no C<--exit>, then we ignore the first ^C. The data feeder
dies, and we behave as if the input data was exhausted. A second ^C kills us
also.

=item

C<--geometry>

If using X11, specifies the size, position of the plot window

=item

C<--version>

Print the version and exit

=back

=head1 RECIPES

=head2 Basic plotting of piped data

 $ seq 5 | awk '{print 2*$1, $1*$1}'
 2 1
 4 4
 6 9
 8 16
 10 25

 $ seq 5 | awk '{print 2*$1, $1*$1}' |
   feedgnuplot --lines --points --legend 0 "data 0" --title "Test plot" --y2 1

=head2 Realtime plot of network throughput

Looks at wlan0 on Linux.

 $ while true; do sleep 1; cat /proc/net/dev; done |
   gawk '/wlan0/ {if(b) {print $2-b; fflush()} b=$2}' |
   feedgnuplot --lines --stream --xlen 10 --ylabel 'Bytes/sec' --xlabel seconds

=head2 Realtime plot of battery charge in respect to time

Uses the result of the C<acpi> command.

 $ while true; do acpi; sleep 15; done |
   perl -nE 'BEGIN{ $| = 1; } /([0-9]*)%/; say join(" ", time(), $1);' |
   feedgnuplot --stream --ymin 0 --ymax 100 --lines --domain --xlabel 'Time' --timefmt '%s' --ylabel "Battery charge (%)"

=head2 Realtime plot of temperatures in an IBM Thinkpad

Uses C</proc/acpi/ibm/thermal>, which reports temperatures at various locations
in a Thinkpad.

 $ while true; do cat /proc/acpi/ibm/thermal | awk '{$1=""; print}' ; sleep 1; done |
   feedgnuplot --stream --xlen 100 --lines --autolegend --ymax 100 --ymin 20 --ylabel 'Temperature (deg C)'

=head2 Plotting a histogram of file sizes in a directory, granular to 10MB

 $ ls -l | awk '{print $5/1e6}' |
   feedgnuplot --histogram 0
     --binwidth 10
     --ymin 0 --xlabel 'File size (MB)' --ylabel Frequency

=head2 Plotting a live histogram of the ping round-trip times for the past 20 seconds

 $ ping -A -D 8.8.8.8 |
   perl -anE 'BEGIN { $| = 1; }
              $F[0] =~ s/[\[\]]//g or next;
              $F[7] =~ s/.*=//g    or next;
              say "$F[0] $F[7]"' |
   feedgnuplot --stream --domain --histogram 0 --binwidth 10 \
               --xlabel 'Ping round-trip time (s)'  \
               --ylabel Frequency --xlen 20

=head2 Plotting points on top of an existing image

This can be done with C<--image>:

 $ < features_xy.data
   feedgnuplot --points --domain --image "image.png"

or with C<--equation>:

 $ < features_xy.data
   feedgnuplot --points --domain
     --equation '"image.png" binary filetype=auto flipy with rgbimage'
     --set 'yrange [:] reverse'

The C<--image> invocation is a convenience wrapper for the C<--equation>
version. Finer control is available with C<--equation>.


Here an existing image is given to gnuplot verbatim, and data to plot on top of
it is interpreted by feedgnuplot as usual. C<flipy> is useful here because
usually the y axis points up, but when looking at images, this is usually
reversed: the origin is the top-left pixel.

=head1 ACKNOWLEDGEMENT

This program is originally based on the driveGnuPlots.pl script from
Thanassis Tsiodras. It is available from his site at
L<http://users.softlab.ece.ntua.gr/~ttsiod/gnuplotStreaming.html>

=head1 REPOSITORY

L<https://github.com/dkogan/feedgnuplot>

=head1 AUTHOR

Dima Kogan, C<< <dima@secretsauce.net> >>

=head1 LICENSE AND COPYRIGHT

Copyright 2011-2012 Dima Kogan.

This program is free software; you can redistribute it and/or modify it
under the terms of either: the GNU General Public License as published
by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.

=cut
